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Tuesday, November 21, 2017

Vixen A70lf Refractor Telescope Review

The Surprise Bargain

It was actually late 2016 when as I was browsing Amazon for what was affordable (to me) in the telescope and accessories section that I saw something I couldn't even believe. The Vixen A70lf 70mm refractor, as shown above, was on sale for only about $80. That's like half price. I spent the next hour scouring the Internet, double and triple checking that I was in fact looking at the model of Vixen telescope that I was sure normally sold for more like $160. I could see that I was looking at a Vixen telescope for sure, but maybe it was an introductory model, or a kids' model, not really the same as the $160 model.

But everything checked out. It was listed as the only one in stock, so I thought maybe they were just dumping it. I was sure it wouldn't sit around at that price for long, so I bought it.

Just a few days later, there it was again on Amazon, back at the original price. I can't explain it. I'm just glad I happened to look on the day I did.

A few days later my order arrived. It was packed kind of like a Russian doll, a big box within an even bigger box. When I unpacked it, sure enough it was the Vixen 2602 A70Lf Telescope. You might wonder why I was so fascinated about the prospect of owning a Vixen 70mm refractor.

The Long Time Desire

The urge for a 3 inch or so refractor started decades ago. I always read, back in the 60s, that for "serious" astronomy you needed either a 3 inch or larger refractor, or a 6 inch or larger reflector. I was kind of corrupted in my thinking back then to assume that those two telescope are more or less equivalent. They of course are not. No way does a 3 inch refractor deliver what a 6 inch reflector does. But a 3 inch refractor does deliver some nice, high contrast images, and has enough light gathering power to reach a lot of targets. So I've always wanted one.

But a good 3 inch or better refractor always seemed a bit out of reach compared to the cost of a much larger reflector, so I've always opted for the reflector. Newtonians generally. I started with a 6 inch f/12 back in high school. Lurched for a 10 inch mirror when in college, and built a behemoth telescope with that (I hadn't read about Dobsonians back then). Eventually got rid of the behemoth and settled for years for a homemade 8 inch DOB.

The First Buy -- Big Mistake

But the thirst for a quality refractor was always there. Then in the late 90s I saw an add for a Meade 90mm refractor on an equatorial mount. It was much less expensive that I expected, going for around $250. That should have set off red flares, no?

But I bought it. It was on a nice enough mount, and a solidly built telescope. It was an f/10, so there was certainly some visible chromatic aberration. What of it, I thought. Moon images seemed pretty nice with the thing. But when the chance came later that year, I found that images of Saturn weren't so good. Try as I could, I was not able to resolve the Cassini division. I thought I should be able to. The more I read, the more I was sure I should be able to. When I later got a Meade ETX 90, I found out for sure that a 90mm telescope definitely can and should resolve the Cassini division.

The Hint Of Greatness -- Small Refractors

Then I read about the influx of Chinese refractors that were being imported. I found that the one I bought was a Chinese import. For sure, today's Chinese import telescopes are pretty top notch, but in the 90s not so much. I got so frustrated with it that I took it off of the mount and put my Jaegers 50mm refractor on the mount. The Jaegers, a gift from a friend, was small but of excellent quality. While clearly not able to reach the stars as well as the 90mm Chinese import, in image quality it was more than a match. But alas, at the moderate tilt of Saturn's rings at the time, the 50mm couldn't quite reveal the Cassini division either.

So I was back to reflectors. Then around 2008, I ran across an astronomy egroup that was devoted to small telescopes, most particularly the 60mm refractor telescope. I joined that, and one of the members generously donated an old vintage Monolux 60mm telescope to me. It needed some tender loving care, but ended up being pretty nice. It easily beat the images of my old 90mm Chinese telescope. So now I knew that a "quality" small refractor could do pretty well. I remember watching a Europa transit with the Monolux, something that would have been a challenge for the 90mm Chinese import. But oh for that 3 inch threshold.

Enter The Long Sought (Amost) 3 Inch

Then along came the Vixen. I mounted it as shown above on my homemade Pipe-fitting Tripod.

Does The Vixen Measure Up?

First, lets just check out the telescope.

The focuser looks pretty substantial. And for a plastic focuser, it is pretty sturdy. But except for the draw tube, it is plastic. The draw tube is pretty long though, at least 6 inches. Yet I really wish it was made of metal.

The business end of the telescope, shown above, holds the quality 2 element objective. The lens cell, again a bit disappointing, is also made of plastic. It, like the plastic focuser, seems ample enough. For me though, a metal lens cell would be more reassuring. Looking through customer reviews, I found one who complained that the lens cell split at the narrowest point near a mounting screw. I've not had that problem, but I'm careful to not tighten them too much.

Of course the telescope comes with a lens hood, as shown above. There is an end cap that fits snuggly into the lens hood when the telescope is not in use.

The telescope also came with a few accessories. Enough to get any astronomer off and running, though in my case I had most of the accessories I already needed.

For eyepieces, the Vixen 70mm came with two PLOSSL eyepieces. One is a 20mm focal length eyepiece, giving a magnification of 45x. The other is a high power eyepiece of 6.3mm focal length, giving a magnification of about 143x. The Vixen seems able to be easily pushed to more like 165x, but the included eyepieces give a user a good place to start.

Also included is a prismatic 90 degree prismatic star diagonal, and an extension tube. If you intend to view without the star diagonal, you'll need the extension to make up for the lack of light travel distance through the diagonal.

A very solid mounting bracket with ringed clamps was included. The bracket is shown above. The clamps, padded on the inside, snuggly wrap around the telescope. It fits nicely with the Vixen tripod if the total package of telescope and tripod is purchases, but is even included if you buy just the telescope. It is the one accessory that is made of metal. It seems quite a sturdy mounting bracket for the telescope.

Ok, so 70mm is a bit shy of 3 inches. Just under a 1/4 inch shy. But that's pretty close. The Vixen is an f/12.9 telescope, having a focal length of 900mm. The Sidgwick criteria for acceptable chromatic aberration suggests that the focal ratio of a telescope divided by the lens diameter in inches should be 3 or greater. It turns out that the Vixen 70mm telescope's ratio is 12.9 / 2.76, or about 4.7. So the numbers say the Vixen should have quite acceptable CA (it does).

The Vixen is physically very light, seems to have a top-notch objective, has an f/12.9 focal ratio, shows virtually no CA, and at 36 inch focal length it still has a reasonable field of view. But all is not perfect. In the focuser image, notice what barely passes as a finder scope. It's a poorly implemented, poorly designed 24mm finder. Each time you use the telescope, you'll have to realign the finder as it never holds position. If you even slightly bump it you'll have to realign it. And it goes without saying that you can't see much through it.

I took the telescope out soon after I received it and got in some moon observing before winter set in. The limb of the moon showed virtually no CA effects. The crater views were crisp and high contrast.

I didn't get back to observing with the Vixen until this fall. On that outing I did get some more moon observing in, and as before, images were tack sharp and high contrast. But on that observing session, no planets were available. So I picked on the double double in Lyra. Some people call it the Lyra Double Double test. I've looked at the double double with many telescopes, and it does provide some indication of optical quality.

The double double, positioned not far from Vega, appears to be a single dim star to the naked eye. Even a finder telescope will reveal it to be a double star. But in a 60mm or better telescope, it is often seen to be two very close pairs of stars. In my long focus 60mm, I can make out all four components at something like 120 power. But one of the close pairs is very close and has stars of unequal magnitude, making the split difficult.

The Vixen handled it well. All four stars could be seen, and the first ring of a nice little diffraction pattern could be seen around the 3 brightest stars. So the Vixen seems to have a very good objective.

It should be said, however, that the double double test is also a test of atmospheric conditions, so if you get a poorer result than you expect should you view the double double, don't necessarily blame your telescope until you try on a couple of other nights.

The crude tripod holding the Vixen in the above image is as I mentioned my old pipe-fitting tripod. The iron tripod is used to hold a number of different telescopes, including my 50mm Jaegers refractor, my 60mm Monolux refractor, my 60mm long focus Carton refractor, my Vixen 70mm refractor, and my Meade ETX 90. It is a work horse.

On the evening when I checked out the Lyra double double, I also used the telescope to examine a healthy sampling of Messier objects. I didn't try to find them all with the supplied finder, I suspect that would have been a frustrating experience. Instead, I used the Star Pointer web utility. It is a handy cosmic target finding utility that lets one dispense with star-hopping, and get down to viewing. It is described on this blog on a different entry.

Star Pointer works with any telescope mount that has setting circles. It works with either equatorial mounts or altazimuth mounts. It works even with my old pipe-fitting tripod, as it has setting circles, as shown above. The setting circles in this case were printed out with a perl program, then glued onto 1/8 inch hardboard and coated with Modge Podge. Homemade, yes. Crude, maybe. Useful, certainly.

With this combination, the Vixen 70mm and the pipe-fitting tripod with its setting circles, I was able to see in a bit over an hour several targets, including M2, M73, M72, M15, M71, M27, M13, M92, M56, M57, M39, M31, and M34. I also viewed the double cluster in Perseus (Caldwell 14), and about four double stars, include Eta Cassiopeiae. That's not a bad haul in that time frame. And I only had to suffer using the finder once, when I used it to position the telescope on Polaris during alignment.

All of the targets showed nicely with the Vixen. I especially enjoyed M13 the globular cluster in Hercules, and the double cluster in Perseus. M13 was easily visible, with just a few sparklers visible at the periphery. The double cluster, super in my f/5 Newtonian but a little anemic in my 60mm telescopes, was very nicely displayed with the 70mm Vixen. With a 25mm eyepiece, the double cluster just filled the field of view, making a very satisfying target.

So what do you get with the Vixen A70lf telescope? Not a galaxy hunter, I admit. But a solid performer even if a bit lightly built with some plastic. You get good optics including the eyepieces and a good performing star diagonal. You get a solid cradle mount which you can adapt perhaps to your tripod, or hold onto should you buy a Vixen tripod later. Or, for a bit more cost you can get the whole enchilada, the Vixen Optics Mini2602 Mini Porta Mount and A70LF Telescope.

I'm pretty happy with the performance and how solid the marriage is between it with its light weight and my pipe-fitting tripod. I think it's going to become my favorite "grab and go" telescope.

Tuesday, November 17, 2015

Finding Celestial Targets -- With Your Cell Phone

How To Locate Celestial Targets

Hint -- near the end of this page you'll find an easy way to find targets with your telescope, but to start, let's cover the familiar star object finding methods.

Finding Stars -- The Common Way

Above is a clip of a star chart from the Xephem planetary program. The red labels have been added. It's a chart of the constellation Hercules, and shows a couple of favorite dropping off points for galactic stargazers: M92 and M13. These favorite Messier objects are Globular Clusters, amazingly compact cluster of stars visible in amateur astronomer telescopes.

Charts like this one have often been used to help find these particular targets, and similar charts to find other targets. Buy large numbers, amateur astronomers in the past located such targets using star charts and the Star Hopping technique. With the advent of so many affordable computerized telescopes nowadays, like the popular Celestron 60LCM Computerized Telescope and the Celestron NexStar 5 SE Telescope, star hopping isn't as popular as it once was.

But users of Dobsonians, like the model at left, and a number of portable 60mm to 70mm refractors and some 90mm Maksutov table-top telescopes still adhere mostly to the star hopping method of finding targets. It involves locating some guide stars near the targets of interest, and  using them as a reference. If the guide stars are naked-eye visible, so much the better.

The technique involves peeking through the finder and locating the guide stars, which may or may not quite all be in the field at the same time. Then, by studying the chart, an estimate is made of where the target is with  reference to these guide stars. In the Hercules diagram above, one might use the reference stars labeled R1 and R2 for example, and notice that M13 is about 1/4 of the way from R1 to R2, almost on a line between the stars.

Thus, one would use their finder telescope or sight to position the view at the best estimate of the target point, then finish finding the target by looking through the main instrument, perhaps  making necessary small sweeping moves to locate the target.

This works rather well, and some accomplished amateurs do so much observing that they know the reference stars and target positions without charts for most of their favorite celestial objects. But for less experienced observers, it can take some time to find what they're after, which may limit them to finding only a few targets in an evening of observing.

A Seldom Used Alternative

Most telescopes purchased with Equatorial Mounts have setting circles on the mounts. The setting circles are easily seen on the image of my ETX 90 above. The setting circle on the polar axis is called the right ascension setting (RA) circle, and the one on the declination axis is the declination setting circle. The RA circle is marked in hours and minutes, like the RA coordinate of stars. The declination setting circle is marked in degrees like the declination coordinate of stars.

Using setting circles can greatly reduce the time it takes to find targets, yet they are not so commonly used. Why is that?

Partly because it can be easy to misread the coordinates of a target from a chart, or on the setting circles. Plus, one must be always looking up coordinates from a star chart or some type of device a couple of times each in order to keep the RA setting current. Finally, the nature of the readings and taking into account Earth's rotation can confuse users.

A main issue is that most amateur telescopes do not have "powered" setting circles. That means the RA setting circle doesn't turn with time to compensate for the rotation of the Earth. If the RA setting circle isn't powered, then the technique for using the setting circles is easy to mess up.

A user with a typical non-powered RA setting circle must start by pointing their telescope (which must be on a properly north-aligned mount) at an easy to find star target, looking up that star's coordinates, and adjusting their telescope setting circles to read the star's chart values. Usually only the RA setting needs to be adjusted.

Then one can look up the coordinates of a desired target that may not be so easily found and use the setting circles to position the telescope for the new target. With luck, the target can be quickly located.

But after observing the target for some minutes. the user has to be cognizant that the Earth has rotated some in the meantime, at about 15 degrees per hour. So a person can't just look up another target's chart coordinates and re-position the telescope expecting to find the new target. The RA setting circle will be off by however many minutes the observer spent on the last target.

The proper procedure is to re-set the RA setting circle to the current target's chart coordinates before moving on. So with updated settings, the cycle is: find a target, view the target, and then re-set the RA setting circle before moving to next target.

Too often, users forget to update the RA setting circle before moving. When this happens, users have to go back to square one, locate an easily found star and use its chart coordinates to update the setting circles.

For many people, this repeated act of reading chart values and updating setting circles, just to read the chart again for a new target and then read setting circles to position the telescope, is just too laborious. So, it's back to star hopping.

Altazimuth Mount Setting Circles

This is where setting circles on an altazimuth mount can be advantageous. Many of us old timers have been taught about the many advantages of the equatorial mount, and certainly for time-lapse astro-photography, an equatorial mount is a necessity. But for observing, nothing is as simple as a basic altazimuth mount. I use my old Pipe Fitting Tripod tripod all the time with a long-focus
60mm refractor. It's the easiest instrument for stargazing that I have.

It turns out that setting circles on an altazimuth mount can make it a very handy instrument for finding star targets. Of course, one can use the star hopping method, but one can also use any of a number of computer tools to get current altazimuth coordinates for targets. Xephm is a good tool for this. Click on a target within the Xephem display and the current azimuth and elevation are displayed in the upper right-hand corner of the Xephem window.

The situation with altazimuth setting circles is a bit different than with equatorial setting circles. Equatorial setting circles are based on a coordinate system where stars have fixed locations on the celestial sphere, but the star coordinate frame moves with respect to the Earth coordinate frame. Thus the need to keep updating the RA setting circle to re-connect the Earth frame to the celestial frame.

The altazimuth frame is a system where each star's coordinates are a function of time, but the setting circles only need to be adjusted at the time one aligns their telescope. No repetitive adjusting of setting circles, but star coordinates are momentary.

I like the system better. For some years I've used a calculator program for pointing my altazimuth telescopes. The calculator program contains a few favorite target lists, like the Messier List. It lets me choose a target, and it then shows me the current azimuth and elevation for the chosen target. A very simple system.

Ah, but you don't happen to have such a calculator program you say, and using a laptop and running a computer planetarium program is too inconvenient.

Then I have a deal for you!

Star Pointer -- The Easy Way

How about a tool that presents all of the targets that are "up" in your location from a selected popular target list, and even tells you where to point your telescope. And that's whether you use an altazimuth mount or an equatorial mount. It also shows the magnitude of the object, and what it is (galaxy, cluster, etc.).

A tool that will run on your laptop, your Chromebook, or even your tablet or smart phone. What would you pay for a tool like that?

How about -- nothing!

Just load the Star Pointer web page into your smart phone or tablet browser, set up and align your telescope, and get started. Pick from the Messier, Caldwell, or Herschel 400 target lists, and start observing, not hunting. Make any telescope you have into a computer assisted telescope by running the Star Pointer web utility on a browser on your laptop, Chromebook, tablet, or smart phone. How handy is that?

All Star Pointer needs is an accurate time setting on your computer device, and your location, within about an arc-minute. With that, it can compute all objects, from any of three available target collections, that are at an elevation greater then 25 degrees. It also displays updated pointing coordinates about every 30 seconds. If you're browser running device has GPS, Star Pointer will get your location automatically.

I've used the program as a pointing aid successfully with my old homemade pipe fitting mount and its altazimuth setting circles, my Long Focus DOB with it's added setting circles, and my equatorial mounted 6 Inch Rich Field telescope. Star Pointer has performed well in every instance.

The altazimuth mode is simple enough. Just be sure your mount's vertical axis is indeed vertical (or the base level), and that the azimuth axis reads zero when the telescope is pointed at Polaris. That's about it. Pick targets from the Star Pointer lists and point to the indicated coordinates.

The equatorial mode is just as simple, but given the previous discussion about RA setting circles and Earth rotation, it needs a little explanation. To use an equatorial mounted telescope, first make sure the Eqatorial mount has a polar axis that is properly aligned. Then select the Init EQ Mount button on Star Pointer, which lists (for the Northern hemisphere) a list of about a dozen bright reference stars. Pick one, and point your telescope at it, which is easy enough given how bright they are. Then adjust your setting circles to read the coordinates of your chosen target.

Unless you happen to leave the Star Pointer web page and later reload it, you're done fiddling with the setting circles. Just pick a target  (they'll now be listed with equatorial coordinates), and point your telescope. As you observe and move to other targets, the Star Pointer program adjusts the presented RA values to reflect the Earth's rotation. So you don't have to keep re-adjusting your setting circles. Just use them.

Can it get easier than this?

A little, perhaps. You can use a computer driven telescope, but many of these are only movable by their computerized motors. Gone is the convenience of just moving a telescope quickly by hand to a new target.

Yet to their credit, computerized telescopes have no real need of a cell phone or tablet web app to know where a star is. Or is that statement a bit premature?

I have a NexStar 5 SE, and to use it I always first looked at my copy of Xephem to see what targets were up. I'd make a list of them, then go out to my NexStar. I'd align it (of course), then start selecting objects from the list. The NexStar doesn't need help with coordinates, it finds the targets on its own. But still -- which targets were "up?" I needed my list.

Not anymore. Star Pointer shows me what's up. It also shows me what's up in azimuth order, starting with the South West. So using Star Pointer, not for coordinates but for what's visible, I can glance at the Star Pointer list and select desired targets from the NexStar controller. By having the Star Pointer display targets in azimuth order, entering from the list facilitates the NexStar in moving from target to target with minimal movement.

So, even though the NexStar doesn't need to know where any given target is, it still needs to be told which one to look at next. Star Pointer gives that information in a useful order.

If you have a simple altazimuth mounted telescope, make some setting circles (get a copy of the Setting Circle PDF), and start using Star Pointer. Already have a telescope with setting circles?, then next time out let Star Pointer help you out.

Monday, May 12, 2014

Petavius, A Lunar Crater Of Wonder

Crescent Moon
I was finally blessed with a clear, relatively calm night recently, so I took advantage and went out to observe Jupiter and Mars.  Mars was still available in this 2014 opposition, and I wanted to get in as many observing sessions as I could while it was still of sufficient angular size.

While my telescopes were acclimating, I could't help but admire the crescent Moon that was still up. I decide to start by viewing some lunar craters, since Mars was still a bit low in the East.

The Moon was in about the phase shown in the image at left. Mare Crisium  was the most prominent feature, surrounded north and south by typical rugged terrain. Since the moon in this early phase is to a direction where I tend not to get great views, I've not often observed the features highlighted in this lunar phase.
60mm x 1000mm

I started my observations with my trusty 60mm x 1000mm Refractor. My pipe tripod mounted 60mm is much like the one in the Orion 24445 Lunar Explorer Telescope Bundle. It's an ideal instrument for this type of viewing, big enough to produce some great images, and small enough to be generally little affected by atmospheric turbulence. Plus, it is ready to go in a hurry, being very portable and needing very little cool-down time.

So I and my 60mm began our investigation of the eastern limb of the Moon. Since the Mare Crisium feature was so prominent, I started my lunar examination with it. I enjoyed perusing the periphery of the mare, looking for craters and mountains that lead into the interior. I also enjoyed the view of the frozen "waves" that stretch across portions of the mare floor. Here and there were small pockmarks that I could make out.

But then, as I explored the more rugged regions along the lunar terminator, I was totally taken aback by a large crater some distance south from Mare Crisium. The crater looked normal enough for the most part, like many of the larger craters in the 60 to 100 mile diameter range. And like many such expansive craters, this crater had a small jumble of hills at its center. But running straight out from the central peaks to the rim of the crater was a thin, straight line, like a spoke. It ran for miles, and was easily noticeable in my 60mm telescope.

I couldn't imagine what it was. It was far too long to be a shadow cast by a central peak, yet so straight it seemed that it must be a shadow. So I changed to my other scope for the evening, my planet busting 6 inch Dobsonian. I could, as I expected, make out a bit more detail, but not enough to tell me precisely what I was seeing. The only explanation seemed to be a fault line, like the Straight Wall, or a deep rille. But it was so straight, it still amazed me.

After viewing that puzzle for awhile, I decided to get to my main objectives for the evening, Jupiter and Mars. Jupiter was interesting as a comparison object on that night, showing mostly the major cloud bands, with a bit of mottling in the NEB. The mottling was just visible in the 60mm, and of course more so in the 6 inch f/10. But there weren't, on that evening, any moon transits or Great Red Spot to examine, and the atmosphere wasn't giving up any more tantalizing details, so I moved on.

My next stop was Mars. On that evening, Mars was only at about an apparent size of 14 arc-seconds, not a very big target. It looked approximately like the image at left through my 60mm, though smaller. That is, what's shown is approximately the level of detail that I saw. Not a lot, but I could easily see the dark feature at the right of the image, which was Syrtis Major. I didn't feel too bad about being able to see features like Syrtis Major on a 14 arc-second Mars with my 60mm telescope.

I was using a 17mm Plossl eyepiece and my 3x Barlow, yielding a magnification of about 180x. I've found that on Mars and Jupiter, being that they are so bright, I can often push the 60mm telescope up to around 200 times magnification.

After viewing Mars for about a half hour, I put up my equipment, and retired for the evening (not enough of a trooper to stay up for Saturn). I'd seen the targets I'd set out to see, and while most anticipating the view or Mars, it was the mysterious crater on the Moon that had provided the most excitement.

Crescent Moon
Since that evening, I've had a chance to go back and research the enigmatic crater with the single linear spoke. Using the moon map included with the Xephem Planetarium planetarium program, I was able to locate the crater I'd seen.

At left is an image showing about the phase of the moon on the night I was observing. I've marked the feature most observers are familiar with, Mare Crisium, the large, dark circular patch near the bottom of the image. The crater I'd ran across that had the strange linear feature was the crater Petavius, which I've also marked.

You may well be familiar with Petavius, but I have to tell you, I was not. And I was definitely not familiar with the odd feature that I saw that evening. It turns out, according to the Wikipedia Petavius Crater article, that the odd, radial spoke feature is a large rille. Apparently, lunar orbiter pictures show the floor of Petavius crater to be full of odd cracks and unusual scars.
NASA/GFSC/Arizona State University Photo

At right is a clear image of the spoke feature I saw. This is a satellite photo, taken from a near overhead position. Viewed through a telescope from Earth, the crater appears more elongated, given that it's seen from a more peripheral angle.

This photo, and others, are featured at Lunar Networks. You can see other strange features in this crater, like the grove that rings the inside left rim of the crater. Another, more sinuous rille is seen moving upward from the center peaks.

So for me it's a mystery solved, but also a reminder that many exciting lunar features lurk near the moons periphery. Features that I've tended to overlook.

The cause of the many odd features on the floor of Petavius remain a mystery for scientists who study the moon. Usually, impacts like that which likely caused Petavius, break the lunar surface and allow lava to flow and cover the basin floor. For some reason, with Petavius this lava coating was incomplete, leaving a major break in the crater floor exposed.

If you're already familiar with Petavius, you're probably laughing at my naivete. But if you're not familiar with Petavius, try looking at that region of the Moon shortly after the lunar phase that exposes it. See if the linear feature of the rille jumps out at you like it did me. I'll certainly be looking for it again. But note that like the Straight Wall, the Petavius rille is a feature that's only easily visible when the Sun angle throws a shadow on the bottom of the rille. If you observe Petavius much after the Moon's crescent phase, that area will be too evenly illuminated to reveal the rille.

And one final point. I remind you that I was able to pick out the illusive rille with my modest 60mm refractor. So if you have a telescope, even a small one, you can likely see the Petavius rille -- when the time is right.

Sunday, May 4, 2014

Mars Observing Hints

If your astronomical juices get flowing every time Mars comes near Earth, then perhaps it's time you learned a few Mars observing tips. After all, you wait over 2 years between Mars oppositions, and Mars only stays near max apparent size for a scant few months each time. So get ready.

Go Long

First suggestion: "Go Long!" 

Say what?

I mean pick an instrument out of your telescope arsenal that has a long effective focal length. The longer, the better. Why?

For one, it's to get the most magnification out of your eyepiece selection. Mars isn't a gas giant after all. At best Mars gets as close as around 35 million miles to Earth, and that's not often. Mars is only a tad over 4000 miles in diameter, about half the size of Earth. And when at closest approach, it doesn't stay around long. Earth laps Mars in their respective orbits and rapidly pulls ahead.
Mars, when on the opposite side of the Sun from Earth, is only about 4 arc-seconds in apparent size. That's about the angular size of a 4 mile diameter crater on the moon. That's small. Don't expect to see much detail when Mars appears that small.

At best, on the infrequent very close approaches, Mars can get to about 25 arc-seconds in size, a size that though small, can yield some tantalizing details to the determined observer. Usually, Mars ranges from around 12 arc-seconds to perhaps 20 arc-seconds at opposition. At the time of this writing, 2014, Mars presented a disc of only about 15 arc-seconds at opposition. So, you'll need magnification, at least 150 times. 200 to 350 times even better.  

Another thing about long focus telescope is that optics of longer focal lengths tend to have less optical anomalies, mostly because long focus optics are easier to make accurately. Longer focus optics in refractors have less color distortion, and in both reflectors and refractors long focus optics have less curvature of field. The depth of field of long focal length telescopes makes it easier to achieve optimal focus since focusing isn't as sensitive. And as it happens, longer focal length optics, because of the ease of construction, tend to be cheaper than short focal length optics made well enough to perform at high magnification.

One thing in your favor is that Mars is quite bright. It's not that much further from the Sun than Earth, so it gets lit up pretty well. So you can push even a small telescope to at least 200 times and still see a nice image. I recently spent an evening looking at a 15 arc-second sized Mars image with a 60x1000 mm refractor, and was able to push it to 200 times without difficulty. The image was amazingly good. I was able to easily spot Syrtis Major, and some hints of other features near the opposite Mars pole.

What are some good telescope options?  A long focus refractor will do nicely. It can be as small as 60mm, like my Long Focus Carton Refractor that I constructed from parts. Most of today's 60mm scopes, while good in optics, come with pretty shaky mounts, so shop carefully or consider making your own mount. You may prefer something a bit bigger than a 60 mm telescope,  say the Orion 9024 AstroView 90mm Equatorial Refractor. On it's equatorial mount, it might be a more capable long term choice.

Long focus Newtonians make excellent and inexpensive planetary telescopes. A six inch f/8 DOB, like the Orion 8944
SkyQuest XT6 Classic Dobsonian Telescope, makes a great all around performer, and performs on the Moon and Planets very well. Even a 4.25 inch DOB, like the Star Gazer Steve 4 1/4 Inch Planetary DOB will do a respectable job on planets.

Maksutov Cassegrains like my ETX 90 work well on Mars and other planets as well. A bit bigger Maksutov that's attractively priced is the Celestron NexStar 127SLT Mak Computerized Telescope. I know, I said go long, and the NexStar 127 or its cousin the Schmidt Cassegrain NexStar 125 appear to be very short. But because of their Cassegrain designs, these telescopes have very long effective focal lengths, great for high magnification. It's only the optical tubes of the Cassegrain designs that are short.

Go High

If possible, observe Mars when it's significantly higher than the horizon, at least 30 degrees. The higher Mars is in elevation, the less atmosphere you are trying to observe through, and the better chance the image will be stable. Take a look at the Seeing And Transparency tutorial to see an animation that shows what poor seeing looks like. Transparency, or how dim of objects you can see, is not particularly important in Mars observing. Sometimes good images occur even when transparency is poor. But you definitely need the good seeing of a stable atmosphere.

Go Late

Mars: ETX 90
If you can, observe late. Of course, you have to observe when Mars is up. But early in an opposition when Mars is rising late, you'll likely get better views. After midnight, the atmosphere often settles down from the churning heat of the day. I obtained my best Mars photo, shown at left, by taking it past midnight at 3 in the morning.

In truth, I started much earlier in the morning than that, perhaps around 1 in the morning. But I was using Barlow projection into a Modified Webcam Astro-Camera, and the field of view of the combination was very small. It took me the two hours to finally get Mars visible on my computer screen so that I could take the photo. But it was worth it. Not a bad image for only a 90mm telescope, yes?

The photo does illustrate that you can definitely get decent results with modest optics, if they are of good quality and seeing is good.  On that 2003 opposition, Mars was near it's max possible 25 arc-seconds in apparent size. Thus the amazing detail for the small telescope.

Be Patient

To wring out the most planetary detail, be patient. For one, your telescope may take awhile to acclimate to the outside ambient temperature. For another, the atmosphere, sometimes even on an unsteady night, may have periods of clarity. So keep looking for those windows of opportunity. Also, once you've noticed the most obvious details, start looking for more subtle ones. You'll be amazed at what you eventually see that you didn't previously notice.

Use A Color Filter

This is not a necessity, but color filters, like those in the Celestron 94119-10 1.25 " Eyepiece Filter Set, can be a real help. Red is the color often recommended for Mars, as the red of the planet will go through the filter, but the darker areas, which can have a blueish tint, tend to get blocked. Thus the non-red areas look darker. On the subject of color filters, yellow is often recommended for observing Saturn and Jupiter.

Try Sketching 

I'm not a particularly good sketcher, though I've had my moments. The images above show one of my best efforts. On the left is a sketch I made of Mars during the very favorable 2003 opposition. I used my 6 Inch Planetary DOB to make the the observations for the sketch. The image on the right is the same as the previous Mars photo. It's the image taken with my ETX 90, and it was taken about 2 days after I did the sketch. You can see that I managed to sketch the major features fairly accurately, as confirmed by the ETX 90 photograph.

You might check out this Astro-Sketching tutorial for some hints about that particular skill. The sketcher in the tutorial took on Moon craters, a much more difficult topic for sketching.

So why sketch? For a couple of reasons. One, you document your session, and some years later you'll enjoy reviewing your sketches, as well as showing them off. Two, it will make you a more attentive observer, able to eke out those elusive details.

Try Photography

Planetary photography is not particularly easy, other than the occasional times you might be able to hold a digital camera up to the eyepiece and grab an image. Even that is hard enough, and doesn't give the best results. My best images have been obtained by using converted Webcams, both a homemade one and a commercial one like the Orion 52175 StarShoot Solar System Color Imaging Camera IV . I have an earlier design, the Celestron NexImage. With it I've managed to get some very nice Moon and Planetary pictures.

But planetary photography is meticulous and time consuming work. The main difficulty is getting the planetary image to show up on the small CCD of the camera. If you don't have the system in relatively good focus, you can have a planet go right through the field of view and not even see it. Once you get a planet into the field of view, obtaining images isn't so bad. My procedure is to take movies (avi files) of perhaps 20 seconds long. The camera takes 10 pictures per second, so that gives me about 200 images to work with from each avi file.

I use a Yorick Language program I created to process frames from my avi files. The program lets me find the highest correlated frames of the movie, then align them and average them. The final output can have contrast adjustments made to bring out the most detail. More time is spent at the computer working with the images than is spent taking them. A program that's available online for processing digital images is RegiStax. It is similar to my Yorick program. It has more features, but I enjoyed the challenge of writing the Yorick program.

The tedious aspect of taking and processing planetary images is another reason you may want to consider sketching. With sketching you get to spend your time observing, and not twiddling with equipment. Even if your sketches come out worse than you'd hoped, you'll still have the enjoyment of having had some great observing sessions.

Hopefully some of the suggestions will help you get the most out of your next Mars opposition. Many of the hints work for Saturn and Jupiter as well.  And the biggest suggestion I can make is to observe as often as you can. You never know when an exceptional night offers up marvelous observing, and it would be a shame to miss those rare opportunities.

Thursday, May 1, 2014

A Telescope Dynamic Duo

Tycho Through 6 Inch Newtonian
At left you see a Tycho photograph I'm pretty proud of. I took it with my 6 inch f/5 Newtonian and an inexpensive Webcam Astro-Camera. I processed about 50 images with a Yorick Programming Language program, averaging the best of the images.

Now that I have whetted your astronomical appetite, I'd like to tell you a tale of two telescopes, one of them being the one used for this photograph.

In The Beginning

Two score and 10 years ago, I got my first big boost in my pursuit of astronomy. I obtained, with the help of my high school principal, parts for a 6 inch f/12 Newtonian telescope. The parts included the mirrors, a mirror cell, an aluminum tube, a secondary spider, and a focuser.

The tube, as it turned out, was barely long enough, so I had to add a bit of an extension. But with the help of a high school friend, I was able to figure out how to assemble the parts and complete the telescope.

I constructed a somewhat crude but functional equatorial pipe mount for the instrument. The mount used smoothed black pipe for shafts, and bronze sleeve bearings.  It was a bulky and heavy mount, just big enough to hold the lengthy telescope.I needed a small step ladder to view through the telescope when viewing high elevation targets.

Then I purchased a copy of Making Your Own Telescope by Allyn J. Thompson. Initially I bought it to get ideas for a better telescope mount, but got excited about the idea of grinding my own mirror. Allyn's book is addictive that way.  He mentioned in the book that a six inch f/4.5 Newtonian would make a great partner for a long focus Newtonian. With this complimentary pair, one would be well equipped to view anything from wide star vistas to minute planetary detail, without compromise.

So I purchased a mirror kit and proceeded to use a summer to make a short focus Rich Field Newtonian. At the time, I didn't know enough ATM to realize that I needed a larger secondary than the one that came with the kit, which was more appropriate for an f/8 mirror telescope. But the objective mirror I ground came out well, probably about 1/4 wave.

Then, I got sick. Yup, I caught a serious case of aperture fever, as indicated by the Aperture Fever t-shirt design at left. Aperture fever is an insidious illness that drives amateur astronomers to aperture excess.

I bought a 10 inch mirror that seemed to satisfy my compulsion. That started me on a new project, even though I'd never realized the benefits of my six inch telescope pair.

I had to adapt my f/12 tripod to accommodate my 10 inch project, which more or less removed the long six inch from contention.

Then, after a couple of post-college house moves, I grew tired of hauling numerous telescopes around. It seemed that the 10 inch was the keeper at the time.

So, somewhere back there I sold my complimentary pair of six inch telescopes -- both of them. Yeah, it was a dumb thing to do.

Forward To The Past

Now, some 45 years later, I'm back to near the optimal telescope pair that Thompson suggested. I have a six inch f/10 DOB (shown on the left), and a six inch equatorial mounted Rich Field Newtonian (shown on the right).  The f/10 DOB I purchased as a custom kit from Stargazer Steve Dodson. The f/5 Rich Field was obtained as a unit from Discovery Telescopes. Alas, Discovery doesn't sell the model I have anymore, but the Celestron 31057 Omni XLT - 150 is very similar.

The Long And Short Of Newtonian Telescopes

There are ample articles about the differences in design and characteristics of long and short focus Newtonian reflectors. I'll only cover the design and operational differences briefly here. After that I thought it might be interesting to talk about differences between my two telescopes in a different dimension. The other dimension concentrating on the fact that one telescope (the Rich Field) is an example of a mass produced product with concentration on popular appeal and convenience, and that the other (the f/10 DOB) is an example of a telescope produced by hand by a master in ATM.

As you likely already know, as to basics these two telescopes are fundamentally similar in both being of Newtonian design. But because of their vastly different focal lengths, the two have significantly different characteristics.

The f/5 Newtonian Optical Characteristics

The f/5 Rich Field is much more typical of today's Newtonian market. Longer focus Newtonian telescopes, even the venerable f/8, are hardly sold anymore except as Dobsonians, like the Orion 8944 SkyQuest XT6 Classic Dobsonian Telescope. Even most Dobsonian telescopes, especially in larger than 6 inch size, tend to be made in relatively short focal ratios. This again is to make them as portable as possible.

The f/5, as is necessary, has a larger secondary than does the f/10. The f/5's secondary is about 30% the diameter of the main mirror. In operation, this means that while it gives twice the field of view of the longer telescope, its larger secondary reduces the contrast it can deliver. The f/5 also shows noticeable coma on the outer 30% or so of the field of view.

It's positives are it's portability and the marvelous wide star fields with which to wow you (and it does -- wow you I mean). Objects like the Beehive cluster, the Andromeda galaxy, the Pleiades, and the Double Cluster in Perseus are the types of items that only wide field telescopes like this can give in all their glory. Thus the commonly used name: Rich Field Telescope, or RFT.

The f/5 requires meticulous collimation to provide sharp images of high resolution targets. But when properly aligned and cooled down, the f/5 can perform admirably, as the initial Tycho photo demonstrates. To get consistent high resolution performance, I resorted to purchasing a Celestron Collimation Eyepiece, which has helped immensely.

The f/10 Dobsonian Optical Characteristics

The f/10 DOB is strong where the f/5 Rich Field is weak. It has a very small secondary, one only 16% of the diameter of the main mirror. This helps it deliver high contrast images competitive with like-sized refractor telescopes. It is less picky about alignment, and offers a flat field -- no coma. The moon, planets, and double stars are targets where it excels. In fact, other than field of view and portability, it performs better than the f/5 in about every optical category.

This quick summary is fairly common knowledge. But that other dimension I mentioned, I think is interesting. Now I'm not out to bash makers of mass produced telescopes. I love my f/5 Rich Field, and in fact it's my most used telescope. But there are some things of which to take notice.

Commercial Design VS ATM Design

A detailed examination of these two telescopes, fairly typical of their respective types, shows what differences in design occur between mass produced telescopes and hand crafted ones. The differences, at least for my two telescopes, don't relate to how sturdily they are built -- both are fine. The differences don't relate to how reliable they are or how long they'll likely last. No real difference there.

The differences have to do with what I'd call optical efficiency. That is, getting the most performance out of the optics. The following descriptions will reveal what I mean.

A Typical Commercial Short Focus Newtonian

I'll start with the short focus Rich Field Telescope. It is a Chinese import, but with American made optics from Discovery Telescopes. The optics are very good. It was my decision to purchase this telescope with a soda lime glass mirror. For a somewhat larger price I could have had a Pyrex mirror. I assumed at the time that in a six inch size, mirror cooling time would not be much of a factor. I think I was wrong.

The f/5 has a rolled steel tube. It's only 7 inches in diameter, which isn't that great for air flow. It also complicates focusing. When I received the telescope, I found that when using short focal length eyepieces or my Barlow, the focuser would extend into the optical path. Not good. Had the tube been a larger diameter, that likely would not have been the case.

6 Inch f/5 Eyepiece End
In the image at left you can see the focuser. It's racked all the way down for storage, but with short focal length eyepieces, it still extended nearly an inch into the optical path. I rather assumed that this played havoc with the diffraction pattern.

The tube is also just long enough to house the optics. The eyepiece end of the tube barely extends past the secondary mirror. This can allow stray light to enter the eyepiece. You can see by the image at left that the spider is just within the lip of the main tube.

The secondary mount (spider) was the three-strut mount shown in the image at left. The struts on this spider were nearly a quarter inch thick. This literally blocked about 4% of the incoming light, and caused 6 horrible broad spikes radiating from all bright objects. This diffraction tutorial gives more details about the effects of different type secondary mounts on diffraction.

The large three-strut spider made a hideous image of the bright planet Mars, making it difficult to see features near the planet's limb. Double stars with bright primaries could easily have dimmer companions hidden in one of the spikes.

6 Inch f/5 Mirror Cell
The objective mirror cell, a sturdy plastic mount that uses the push/pull type of alignment adjustment, was designed to seal off the bottom end of the telescope tube. I think this served the dual purpose of acting like a lens cap, and making the plastic mirror cell sturdy enough to do its job. But this hinders air flow, and thus significantly extends cool down time -- especially with the soda lime glass mirror.

So while the tube and tripod are plenty sturdy and functional, the optical efficiency is impacted by the minimal sized tube, the closed nature of the tube, the extension of the focuser into the optical path, and the thick-strut spider. The emphasis on making the smallest, most portable six inch reflector possible came at some cost.

A Typical ATM Master Telescope Design

So now consider the Stargazer Steve DOB design. The f/10 planetary DOB has an over-sized sonotube. Sonotubes are renowned for their thermal characteristics, and the tube for this particular telescope is over 8 inches in diameter -- what ATM experts suggest. The air currents that crawl along the inner wall of the tube are out of the optical path.

The mirror cell does not block off the tube, but allows ample air flow through the tube so the mirror can stabilize more quickly. The objective mirror is Pyrex on this telescope, and the cool down time difference between it and the f/5 mirror is significant, being only about 1/2 hour for the f/10, and well over an hour for the f/5.

6 inch f/10 Eyepiece End
The eyepiece end of the tube extends at least 8 inches past the secondary, which helps block out unwanted stray light.

The diagonal mirror is minimum size for the telescope length, reducing diffraction issues to a negligible amount.

The secondary mount (spider) is of a thin metal curved design. Minimal light is blocked, and there are NO diffraction spikes. This helps deliver refractor-like performance.

The Difference Is In Optical Efficiency

So when you compare the aspects of the two telescopes relating to the optical path and optical environment, you can see that what an ATM master delivers gives about the best performance out of a set of optics that you can possibly expect. The mass produced telescope delivers a solid instrument with fine optics in a desirable and popular package -- but not one with optimal optical efficiency.

The Silver Lining 

The good news?  Since the f/5 is of the simple Newtonian design, I was able to tune out most of the foibles. I did that on my f/5 telescope, leaving it still a very portable and easy to use telescope, but with significantly better optical efficiency.

I started with the focuser issue. I moved the objective mirror forward about 3/4 of an inch, which was the minimum necessary to let the focuser stay out of the optical path when using even my shortest focal length eyepieces.

I put black flock paper on the inside of the telescope tube, which with it's total non-reflectivity, helps mitigate any problems from stray light. One could also add an extension to the eyepiece end of the tube, but this would impact the portability and ease of transporting the telescope.

6 inch f/5 Curved Spider
I removed the thick three-strut spider and replaced it with a thin, curved metal spider. Now the amount of light being blocked is only about 1%, and there are no spikes when looking through the telescope, even on the brightest targets. You can see the curved secondary mount in the image at left. Now isn't that better?

I was going to replace the tube with a larger diameter and longer sonotube, which would have cut down on mirror thermal instability, but would have impacted portability. I was initially willing to make that trade off, but I didn't want to risk damaging the objective mirror. The mirror is glued to its current mirror cell, so I decided not to risk trying to remove it. Since the current cell would not adapt well to a larger sonotube, I scrapped that upgrade.

So I still have the rolled steel tube, and the mirror cell still seals off the bottom end of the tube. It mainly impacts cool down time, which is usually of little consequence since the telescope is primarily used for viewing wide star fields at low power.  If I want to view a mix of stars and planets on any given evening, putting the planets last on the list usually provides the required hour or so of cooling time necessary for reasonably good viewing.

Can You Improve A Well Built DOB?

6 inch f/10 DOB Wheels
As to the f/10 DOB, there wasn't much I could do to improve it, optically at least. I did add small brackets along the bottom of the base so that I could slip an axle with wheels in place. This way I don't have to lift the telescope off of the base and move the instrument in two trips. I just roll the telescope into place and slightly tip the base and remove the wheels.

Even with the wheels, however, my DOB wasn't any easier to find star targets with. Not nearly as convenient as the clever push-to telescopes like the Orion 10018 SkyQuest XT8i IntelliScope Dobsonian Telescope. The Orion IntelliScopes use angle encoders and a small computer to tell the user where to point in order to find objects. Thousands of objects are available in the computer. For those of us who are not effective star-hoppers, this is a magnificent convenience.

Failing that level of convenience, I was able to add setting circles to my f/10 DOB. It took me awhile to figure out how to do that, and in the end I didn't figure it out as much as copy the techniques of another person at the Manual DOB Setting Circles webpage. I had to alter the designs a bit to fit my mount, but found the basic ideas to be of great help.

6 inch DOB AZ circle
At left is an image of my DOB azimuth setting circle. I printed out a precise circle with a Perl language program, making the circle as large as would fit my mount. I lifted off the rocker box and glued the setting circle on the base. Then I cut a slot in the rocker box of the mount to reveal a section of the setting circle.

I added a pointer (just visible in the image), and by peaking into back of the rocker box I can set the telescope azimuth. I get the azimuth and elevation from either a calculator program I use, or a laptop program. One could use a computer planetarium program on a laptop.

As long as the base is setting reasonably level, either of my programs will let me align to north, and enter an azimuth bias if the mount isn't perfectly aligned with Polaris. The azimuth bias feature helps in that I don't have to take inordinate time to perfectly align the telescope base with north. I just get within a few degrees and inform the respective program of my alignment error.

Then either program will let me choose an object out of one of a few target lists, like the Messier list. Once a target is selected, either program will provide me with the correct azimuth and elevation of the target -- accounting for the azimuth bias.

6 inch DOB Elevation Circle
 Elevation is simplicity in itself. I'd have never thought of it without the article I found. I use a dial level that happens to have a magnetic base. It was easy to affix a small metal plate to a side of my hexagonal telescope cradle because of its flat surfaces. I can plop the level onto the plate and be off and running.

So, yes I was able to improve, slightly, my well designed DOB. But not pertaining to it's optical efficiency, which was already optimized. However I have  made the instrument easier to use, and decreased significantly the challenge of finding star objects. With my version of computer assist, inspired by the commercial push-to design, I can use the telescope to easily locate and observe any of hundreds of targets.

Hopefully you've found the comparison of long and short Newtonian telescopes informative. And if you're a tinkerer, perhaps you've been inspired to add some features to either your commercial or hand-made telescope. For me, like many of you, I find tinkering to be part of the entertainment of the astronomy hobby.

Wednesday, November 27, 2013

An LED Gun Sight Telescope Finder

Monolux 60mm Telescope
Recently, before the fall weather turned rotten, I finally got a chance to do a bit of observing. The summer had provided little opportunity, given a copious amount of windy and cloudy weather, which was followed by a very busy fall that occupied my time. So my previous observing session had been some time ago.

I was pleasantly surprised when my adult son, who has rarely shown any interest in my hobby, wanted to go out and observe with me. Because of his inexperience, I decided to use my handy Monolux 60mm refractor, pictured at left. On its more than ample pipe mount, it handles easily, and makes a very simple telescope to use.

We went out early, given that it was already dark even at 6:00. I sometimes level the tripod so that I can use a calculator assist program for locating objects, but on this evening I decided to just go for some targets I could easily find. I selected a range of target types, so that my son would get an idea of what I enjoy about the hobby. Did I say hobby? Perhaps obsession is a better word.

Ptolemaeus Region Through ETX 90
We started with the 1st quarter moon. The terminator running down the center of the moon provided ample craters and shadows to keep us occupied for some time. The Monolux delivers the moon with wonderful clarity.

I enjoyed Albategnius and Ptolemaeus as I often had before. But as shared viewing with a novice often dictates, I spent most of the time finding new targets for my son and repositioning the view, given that the telescope was on an unguided mount.

After the moon, we took in the Pleiades (M45), which the FOV of the 700mm focal length Monolux was nearly able to reveal in its entirety. M45 was pretty low in the east, so not as magnificent as when viewed higher in the sky.

Next was the double double in Lyra. Because of the unguided mount, I chose not to go much above 100x, so we really didn't clearly split all components. I have split them with the Monolux before, but splitting the double double with the Monolux requires more magnification and some viewing experience.

So I moved on to the Ring nebula (M57). With a quarter moon and a 60mm telescope, I wasn't sure if we'd be able to actually see the Ring nebula, but we could. It showed up as a small but discernible smokey ring. I was impressed.

The next target was M13, the wonderful globular cluster in Hercules. It was discernible also, but being so low in the west it wasn't spectacular. With the 60mm, it showed as a patch of fog, and individual stars could not be detected. It did, however, give me a talking point as I tried to explain what a globular cluster was.

I contrasted that with the double cluster in Perseus. The side by side open clusters are a favorite of mine, and the relatively large FOV of the Monolux allowed both to be seen in the same field. It was a bit disappointing, however, as I recalled my oft views of the sight with my 6 inch f/5 Newtonian. Naturally, the Newtonian presents the double cluster with more pazazz.

After that we took in a view of the Andromeda Galaxy, M31. Again, it was easily visible in the 60mm telescope, but certainly less than spectacular because of both the telescope size and the competing quarter moon. It was, however, another good talking point, as I was able to explain that all of our other targets for the evening had been local Milky Way objects, but M31 was some 2.5 million light years away, far beyond the confines of our galaxy.

f/5 Newtonian Rich Field
To complete the evening, I moved the telescope over to Eta Cassiopeia. It's a somewhat challenging double star for the 60mm, with the companion star being rather dim. But it still gave us the opportunity to round out our target types.

Time For A Bigger View

A couple of nights later, I wanted to show my son the same sights through my favorite telescope, my f/5 Newtonian Rich Field. As shown, it sits on a sturdy equatorial mount, and has a clock drive. I thought the clock drive  would make observing a bit easier for my son, because the targets would stay in view.

I went out during the day and used my collimation eyepiece to check the telescope's mirror alignment. It had been many weeks since I'd last used the Rich Field instrument, after all. I was pleased to see that it had held collimation very well, and needed no adjustment. As a short focus instrument, for good image quality, accurate mirror collimation is essential.

Enter Murphy's Law

Rigel Quick Finder
That evening when darkness arrived, I headed for my workshop/observatory to get the Newtonian so I could set it up, only to find that the last observer had apparently been the infamous Murphy, of Murphy's law fame.

Murphy's presence became apparent shortly after I retrieved my trusty Rigel Systems Quick Finder. It's a super handy 1x finder that projects a red reticle into the night sky, making finding objects a snap.

Mine came with 2 bases, so I had installed a base on both my 6 inch f/5 Newtonian, and my 6 inch f/10 planetary DOB. That way I could use the finder on either telescope.

But on this evening, when I tried to insert the finder into its base, it wouldn't snap into place. After several tries, I looked more closely to see what was wrong. And Murphy's work became apparent.

On the back side of the finder, as shown at the bottom of the image at right, is supposed to be a flexible foot that clips into a slot in the finder base. As you can see, there is no longer a foot, just a hole in the base where the foot was.  The foot had broken off.

So, there would be no using the Newtonian that evening. While I could have found the moon without a finder, the other objects would have been virtually impossible to locate.

And what was so frustrating, was that not only was the 6 inch Rich Field out of commission, but so was my 6 inch Stargazer Steve Planetary DOB, since I used the Quickfinder on both.


That evening we still went out, but had to settle for views through my handy Meade ETX 90. It has excellent optics, and a clock drive to boot. So it was a step up over the Monolux of the previous observing session. But for star objects, not a very big step up. Besides, with the small elbo finder available on the ETX, finding dim objects like the Ring Nebula and the Hercules Globular Cluster were very difficult. So the moon looked great, but the other targets didn't give the punch I was hoping for.

Rolling With The Punch

I was a bit down about the broken Quickfinder. I tried a repair, but it didn't work. I was about to order me another one (I love that finder), when I remembered that some time ago my older son had given my a couple of inexpensive rifle sights that projected a red dot onto the target. My son had nabbed a couple of the NcStar Tippmann Red Dot Reflex Sight devices for half price, and then decided he didn't need them. He thought I might have a use for them.

Red Dot Gun Sight

So I finally found where I'd cleverly stashed them. I noticed that they were very similar to the sight on my Celestron NexStar 5SE, except that the Celestron sight had an adjustable intensity control for the reticle. My inexpensive Red Dot finders didn't have that adjustment, but did have adjustments for azimuth and elevation.

I decided that for the price (free), it was worth a try to see if I could find a way to use the sights. I had two telescopes that were short a finder, and two Red Dot sights, how perfect could it be?

The Red Dot finders are designed to fit on a Weaver Rail. They have a slot on the bottom (see arrow) and clamps on either side of the slot that can grip the rail. I thought that it shouldn't be too hard to fabricate something that would mount to the scope and fit in the slot along the bottom of the Red Dot sight.

Gun Sight Mounting Block
What I came up with was the simple wood block shown at left. It was cut from a 2x4. It was cut to the length of the slot on the Red Dot, and has a tongue along the top just wide enough to find snugly into the slot on the bottom of the sight.

I cut it out with my table saw, but this piece is so simple one could do it with a hand saw and a little patience.

I used rough grit sandpaper to form a curve on the bottom of the wood piece that would let it sit properly on the telescope tube. That left only drilling a couple of holes in the tongue part to accomodate the Red Dot sight.

Fastening The Sight

Gun Sight On Block

The image at left shows how the sight sits down on the tongue along the top of the block.  All that was left was to mark and drill holes that would align with the sight holes, and fasten the sight on with screws.

I didn't even need to use the clamp pieces, since the tongue was cut to fit snugly into the sight base. A bit of black paint and a screw to mount the block to the telescope finished the project.

Gun Sight On Telescope
The finished product is shown at left. 

So how does it work? Better than I'd have thought. The projected dot is rather bright, and I can't actually see stars through the view window. But, using both eyes, one eye looks through the sight and sees the dot, and the other looks past the sight and sees the stars. So I see a dot imposed upon the background of stars. After picking a bright star and tweaking the alignment knobs, I was easily able to find all of the targets on our original observing list.

I read one online article that suggested one could put a drop of fingernail polish on the LED to dim it down a bit. I haven't tried that solution yet.

On the evening my son and I used the Newtonian, he got to see rather astounding views of the Pleiades, the double cluster, and the Andromeda galaxy. What a difference 4 inches of extra aperture makes.

What's left to do? Just mount the other Red Dot onto my planetary DOB using the same technique, and everything will be back in order. Perhaps Murphy will take the hint and go bother someone else for awhile.