Book Mania

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.

Saturday, June 29, 2013

My Celestron NexStar 5SE Review

My Optical Arsenel
At left you see a composite image showing much of my collection of telescopes. Starting at top left, you see my 60mm Carton refractor, my ETX 90 RA, my  NexStar 5SE, my 6 inch Newtonian, and my Stargazer Steve Dobsonian. Not included are a couple of small refractors.

I show these because they are the telescopes the represent the greatest variety. The favorites of these at the moment are the 60mm refractor and the Newtonian. I have fun with the collection not only because of the range of sizes and portability they provide, but they are each quite different optically. One refractor, one Maksutov Cassegrain, one Schmidt Cassegrain, one Rich Field Newtonian, and one long focus Dobsonian. It is that diversity that gives me enjoyment, with each of the collection offering views with particular characteristics. And, I imagine you can see, none of the instruments are expensive to own.

I purchased the Celestron NexStar 5 SE Telescope  used from an astronomy egroup friend. It hasn't made it's way into "favorite" status yet, but it may well edge out one of the others in that category. Since getting it, I've been using the NexStar side by side with others of my arsenal to see how it measured up. I wanted to find out how good the optics were, and how convenient (or not) the mount was.

The NexStar is a computerized telescope. Once it's aligned, just use the controller to select an object to view. I'm still getting used to it. For years I used a calculator program to tell me where to point my non-computerized telescopes. Now, I use a cell phone and the Star Pointer web site utility. It provides handy computer assist to any telescope, altazimuth or equatorial, that has setting circles.

Optics-wise, with my early trials of the NexStar 5SE I was favorably impressed. While I'm not sure I'm a fan of the GOTO mount just yet, the optics of the telescope are excellent. On early observing trials, I was just using Polaris as an alignment star. Peeking into the eyepiece, I noticed a quite obvious companion of Polaris. The companion I spotted is within the range of a number of my telescopes, yet I'd never noticed it before. The NexStar virtually stabbed me in the eye with the companion.  I was impressed.

On that same evening, I had the opportunity to observe the Plato region of the moon, and it was fortuitously  illuminated for good detail. Again, the NexStar virtually poked me in the eye with the view of about 3 craterlets on the floor of Plato. I've hunted for Plato floor craterlets before with other telescopes, and usually came away without success. But there they were, clearly visible, their impact splashes easy to discern. I looked with my 6 inch f/5 Newtonian, and sure enough it also revealed the craterlets. But, they were not as obvious as when observed through the NexStar.

More recently I decided to do comparisons between each of the telescopes you see in the arsenal by looking at Saturn. I started out one evening by looking with my 6 inch Stargazer Steve DOB. It's especially designed, at f/10, to be a superior lunar and planetary telescope. It has a Pyrex mirror, an over sized tube to help ventilate, a small secondary to minimize diffraction, and a very steady mount.

It showed Saturn superbly. The Cassini division was easy, as was the lighter colored equatorial band around the planet. Also easily detected were 3 of Saturn's moons: Titan, Rhea, and Dione. Stargazer Steve's telescope delivers. The only issue with the telescope is that because of its size, it is a bit more clumsy to use, and it's ultimate capability is usually limited by the atmosphere. It's always a bit of a disappointment when I endure the longer setup time the telescope requires, only to see that on that evening a smaller, easier to set up telescope would have sufficed.

Next I tried the NexStar 5SE on Saturn. To my surprise, the image was nearly as good as the one produced by the planetary DOB. The view was just not quite as bright, with Rhea and Dione a tad more difficult to see. The only other difference is that the Stargazer Steve low center of gravity mount was steadier than the NexStar mount.  But those were about the only differences. Again I was impressed with the optical quality and contrast capability of the NexStar.

The next evening I paired up the NexStar 5SE with my 6 inch f/5 Newtonian. I'd recently bought a Celestron Collimation Eyepiece to more precisely align the optics of the short focus Newtonian. Once I used the collimation eyepiece, I released that probably about 75% of the time, I'd been using a marginally or poorly aligned telescope. With the collimation eyepiece, I knew that the alignment was spot on.

Looking through the Newtonian first, I saw a nice image of Saturn, with the Cassini Division and the same 3 moons easily visible. But when I looked through the NexStar  5SE, the image was even sharper. It was slightly outperforming the short focus 6 inch Newtonian. I was happy with the NexStar, but a bit disappointed that the Newtonian, even with meticulous collimation, had a slightly softer image. None-the-less, the rich field Newtonian still makes a super star telescope.

Saturn Through ETX 90
A few nights later I viewed Saturn with my trusty old ETX 90 (now superseded by the Meade 3514-04-15 ETX MAK 90-Millimeter Telescope), whose images always astound me. The view looked a bit better than the 2012 ETX 90 photo of Saturn shown at left. Other moon and planet photos taken with the remarkable ETX 90 are shown on my ETX 90 Astro-photo web page.

Except for the brighter image that the NexStar 5SE delivers because of its larger aperture, the ETX 90 view of Saturn was surprisingly close. The Cassini Division was easily visible, though not quite as stark as shown in the NexStar, and the same 3 moons were visible. However, seeing Rhea and Dione with the ETX 90 required some time and considerable use of averted vision. A pleasing view, however. Was the NexStar view better? On that evening, just a bit. On evenings with a more cooperative atmosphere, I think the NexStar's potential would be more noticeable.

And finally, I got an opportunity to check out Saturn with the modest sized 60mm refractor. Some of you who jumped into the hobby with larger telescopes than the Venerable 60mm probably think that comparing a 60mm view with the likes of the other telescopes in my collection would be pointless. I beg to differ.

I've looked at Saturn many times over the years, and for awhile I was using an early version 90mm Chinese made Meade refractor. Try as I might with that 90mm, I could never quite make out the Cassini Division. I understand the currently made Chinese refractors are much better, but my early version didn't deliver the quality of images I expected.

But on this Saturn trial, with the excellent Carton 60mm lens at the business end of my telescope, I was able to see the Cassini Division. I could also see the planetary equatorial band, though with less contrast than seen through the bigger telescopes. The view was very nice indeed. As to the moons, I was only able to see Titan for certain, thought it seemed that at times I'd glimpse either Rhea or Dione.

So, what did I learn? The main thing I learned was that the NexStar 5SE has the potential to become one of my workhorse telescopes. The optics are very good, and the computerized mount fairly easy to use, if just a bit shaky. I think the NexStar is a keeper, and hopefully some planetary photos through the NexStar will be forthcoming. For the first summer of use, I struggled a bit with a flaky power switch on the NexStar, but I found that Celestron has a market place for parts, and I was able to find the exact replacement circuit card with the power switch. Now with a new switch, the NexStar works flawlessly.

I also rediscovered what I already knew, that comparing views through different telescopes, especially different types of telescopes, is a real blast. In this little project, I was able to compare views of Saturn not only through some different sized telescopes, but different types as well. The long focus refractor, the Maksutov, the Schmidt Cassegrain, the short focus Newtonian, and the long focus Newtonian each provided a pleasurable viewing experience.

Finally, I learned that both the quality 60mm and the ETX 90, as others have said, run out of light before they run out of image quality. The NexStar 5 SE, like the two 6 inch reflectors, tends to run out of seeing before it runs out of light. But the ease of setting up the NexStar suggests that it's still a great candidate for a first choice grab. It's as easy to set up as any telescope I have, is as portable, and provides excellent performance.

What's left for me to evaluate is whether I can adjust to using the Celestron computerized mount. I'm so used to manually movable telescopes, both altazimuth and equatorial, that having to do all telescope movements through a keypad still seems awkward to me. Now a Celestron 5 inch SCT on an equatorial mount -- that would peak my interest.

Friday, April 5, 2013

Praise For The Venerable 60mm Refractor

At left you see an image of one of my favorite telescopes, my 60x1000mm Carton refractor. Yes, that is a homemade pipe fitting mount you see holding the telescope.  Click on the link to see how to make your own.

What brings me to this post is the experience I had most recently with this particular telescope. An experience that reminded my of why I enjoy it so much.

Not long ago I acquired a NexStar 5SE from an online acquaintance, and have been furiously learning how to use it, and comparing it to some of my other telescopes. There'll be more on that effort in another post.

But one consequence of comparing telescopes is that you find yourself very busy in the mechanics of observing, like locating the same object in each instrument, adjusting magnification in each to be comparable, and straining to see tiny details or the dimmest stars in the compared views.  But what you don't tend to get out of that experience is the simple enjoyment of viewing each target in a relaxed setting.

So recently, instead of another evening of tests, I wanted to just go out and enjoy an evening under the stars. Enjoyment for me means using a telescope that is easy to set up. It also means using a telescope that is easy to operate. And, finally, using one that lets me effortlessly find targets, so I spend the evening observing, not searching, or struggling with the apparatus.

For me, that usually means grabbing one of my two 60mm refractors. I have a 700mm focal length resuscitated Monolux, and a slapped together from available parts 1000mm focal length Carton. That is, the objective lens is made by Carton. See for yourself the simple construction of the Carton Refractor Telescope.

In case you feel at this moment that there is madness in thinking one can enjoy star gazing with a mere 60mm telescope, I challenge you to read on.

A Wonderful Madness

Take the other night as a case in point.  In only an hour and a half or so of observing with my 60x1000mm Carton, I observed Jupiter and a host of Messier objects, plus a couple of nice double stars. The Messier I observed were open clusters M46, M48, M35, M36, M37, and M38.

I also observed the M3 globular cluster, the M42 Orion nebula, and galaxies M81 and M82. I could just get both of the galaxies in my field of view when using a 25mm focal length Plossl eyepiece. I also took a peek at M45, the Pleiades. With the 1000mm focal length, the Carton telescope didn't quite span the extent of the beautiful Pleiades, but the 700mm focal length Monolux can, and delivers a fantastic view of the sparkling stars of the Pleiades.

Now that's not a bad evening, especially considering that a great deal of that time was spent in watching Jupiter and 3 of its moons. Ganymede and Io were approach Jupiter from one side, while Europa was approaching from the other. I hadn't checked my almanac that evening, so I wasn't sure from which side of approach the moons would cross in front of the planet, and from which side the moons would disappear behind the planet.

So I spent considerable time watching what turned out to be Io and Europa inching closer and closer to the planet. I knew that if I waited long enough, one or the other would pass in front of the planet (the other passing behind), making a shadow that I thought I'd be able to see with my 60mm.

I have seen Io's shadow with a 60mm before, so I was pretty confident in my instrument. But, as it happened, the shadow was going to become visible too late, and I'd already promised my spouse I'd come in and watch a mystery movie.

So how did the Messier look through my modest 60mm?

All of the open clusters, the Pleiades, and the Orion nebula were very enjoyable views. M3 was clearly visible as a dense, small cloud. The M81 and M82 galaxies were the toughest targets for the 60mm. They were easy to see, but appeared as ghostly objects. Still, I could tell that one was a fat elliptical object, and the other a very thin (edge on) elliptical object.

Pipe Mount Setting Circles

How do I find the star targets?

As the above image illustrates, I've added setting circles to my simple pipe-fitting mount. With the setting circles, all I need now is my cell phone, and I can find any Messier, Caldwell, or Herschel 400 object that is within grasp of my telescope.

How, by calling for help?

No, by using the Star Pointer web site, which presents a utility that if allowed to use your Latitude and Longitude location, call tell you in real time where to point your Altazimuth or Equatorially mounted telescope. It presents pointing coordinates for either coordinate system, and updates the coordinates every 30 seconds. Telescope with setting circles, cell phone, and a warm coat -- that's all I need.

Some Good Reasons To Use A 60MM

Here's a list of my reasons that I think justify use of such a modest instrument. The list is predicated on two things: that the telescope is of good quality, and that it is solidly mounted. Does that mean you need a $600 telescope and a $300 mount?


You can use a vintage 60mm from the past, typically available on Ebay for maybe $150, or at a garage sale for considerably less. Tune it up a bit, and you'll find that those old 60mm telescopes were no kids' toys.

And you can make a Pipe Fitting Mount as I did for only tens of dollars. And that pipe mount will be the most solid tripod you'll likely ever experience. Mine is made with 2 inch diameter pipe with polished and lubricated threads on the turning axes. You can find instructions on the link.

With that size pipe, a telescope balanced in its cradle lets me just point the telescope and look. I don't need set screws or slow motion controls. A light tap on the telescope will move it a few arc-seconds to adjust the target position, and the vibrations damp out immediately. I can focus without causing any vibrations -- the only telescope I have, commercial or otherwise, that's rock solid enough to let me focus without inducing vibrations.

I use a "push to" method for locating objects. I have an old HP 48 calculator programmed with the necessary math and 3 star catalogs so that I can simply select an object from one of the catalogs, and the calculator displays the azimuth and elevation for that target. If you aren't interested in programming a calculator in a similar manner, you could alternatively use a laptop and something like Xephem to give the same data. You could probably even find a smartphone or tablet app that will give you azimuth and elevation information for astronomical targets.

Since the pipe mount has setting circles on it, I just move the telescope to the selected coordinates, and if I've done a decent alignment of the telescope, the object will be somewhere in the field of view.

What does the alignment procedure consist of? Even that is simple. I level the base, which has two of the three feet made from threaded bolts, making leveling easy. Then I point the telescope to Polaris and turn the azimuth wheel to read zero -- done!

As to the calculator, I look up the current Sidereal time for my location before I go out (I use the Xephem Planetarium Program for that, but you can just look it up with the Sidereal Time Calculator). I enter that Sidereal time into my calculator, and it's set for the evening. It has it's own internal clock, so it can propagate Sidereal time during my observing session. And, as pointed out earlier, if you're not the computer nerd I am, just use your laptop and a planetarium program.

Once I've obtained a target's azimuth and elevation data, I just move the telescope to the indicated angles. With the heavy-duty pipe tripod, there's no need for clamps or slow motion controls -- it couldn't be easier.

Oh, and did I mention that a 60mm refractor can be producing great images within only a few minutes after setup? No need for an hour or two cool down. By the time I level my tripod and align on Polaris, I'm ready to start observing.

One more advantage of the 60mm size telescopes -- portability. The telescope and tripod, even my pipe mounting one, can be left assembled and moved around without any disassembling. Mine sits ready for action in my shop. Of course, I keep the telescope tube ends covered when it's not in use.

So there you have it, the 60mm is:
1) Quick to set up.
2) Reaches thermal stability quickly.
3) Alignment is easy.
4) Push to makes finding objects quick (or star hop if you prefer).
5) Rock steady views with a very simple mount.

But Can You See Anything?

You can see a great deal. Nearly all of the Messier (some say all) can be seen with a 60mm, if you have a reasonably dark viewing site. Granted, the galaxies are dim, but most are visible. And the star clusters are great.  There are many double stars that 60mm refractors can do wonders with. And cloud bands on Jupiter, Saturn's rings, the phases of Venus, and even some details on Mars can be seen.

Jupiter through 60mm
On a clear evening, Jupiter, for example, can reveal some tantalizing details. The image at left, was taken through my 60mm Carton using a Celestron NexImage webcam.  Actually, you can often see more detail than is captured in this image, though in a 60mm the colors don't show up as in this image.

Do you notice anything unusual about this photograph? The SEB (South Equatorial Belt) is missing! This photo was taken in 2010, when the mysterious SEB did it's occasional disappearing act. It's back now (2013,) so don't despair. But just note that the disappearance and reappearance of the enigmatic SEB was quite visible through a 60mm telescope.

Plato through 60mm 
And the moon!  Eat your heart out. The image at left was taken of the Plato region (one of my favorites), using my Celestron NexImage webcam and my 60mm Carton refractor.  The individual mountain peaks Piton and Pico are easily visible, as well as is the Alpine Valley.

Imagine trolling over the moon at such detail. You can, with just a decent 60mm refractor on a solid telescope mount.

Tycho through 60mm
The moon through a 60mm shows a wealth of detail. And each time you go out to look, the sun is illuminating the moon at a different angle, leading to different details.

This image of Tycho, also taken with the NexImage and my 60mm Carton refractor, shows one face of Tycho. At this sun angle, the internal structure of Tycho is revealed, showing a large and small mountain peak at the crater's center. Not bad detail for a 60mm. But during a full moon, the fantastic ray system of Tycho dominates instead of the intricate details shown here.

Additional photos taken through my 60mm Carton can be found at my 60mm Astrophotos webpage.

So don't let anyone tell you that your 60mm telescope, if you have one, is useless. That's true only if the telescope sits in a closet all the time. Get it onto a good mount, obtain a few decent eyepieces, and go for it. While I don't use a 60mm all the time, as I have some larger telescopes, it's certainly the quickest scope to set up that I have, and additionally the easiest to use.

Thursday, February 21, 2013

How To Collimate Your Newtonian or Dobsonian

Near the close of last year's observing season, just before it got too cold for me, I had to admit something dreadful about my 6 inch Discovery telescope. I've always considered it, and the similar Celestron Omni XLT 150mm, to be nearly the perfect telescope type. Compact, relatively inexpensive, and good for a wide range of observing.

And while I love my Discovery telescope, especially after some modifications I made to it, I none-the-less had to admit that the images it presented were often sub par.

I particularly noticed this when I did side by side comparisons between it and my ETX 90 Maksutov. I used high resolution targets like Jupiter and Saturn as comparison objects. I was disappointed that the ETX, with only 3.5 inch aperture, would give as good or better images as the larger 6 inch reflector.

My rich field is an f/5, and I know of many people who successfully use similar focal ratios and get good planetary images. I was concerned about this mediocre performance. I've used Newtonian reflectors for decades, from long focus to short focus, and I was pretty sure I knew how to properly align the optics in them. So assuming I knew what I was doing, what was the problem?

Did I need different eyepieces, more expensive ones that would work better with the short focal ratio of the telescope? Did I need a new objective mirror? Did I need a new and better Barlow lens? Did I simply need to accept poor images at high power because the telescope was a rich field, and resort to only using the instrument for general star gazing? I decided to get to the bottom of the problem, hoping that some kind of affordable accessory purchase would help me improve the performance.

With some critical observing on some close double stars, I observed what appeared to be astigmatism. I did the usual tests, rotating the eyepiece to see if the astigmatic image rotated with the eyepiece -- it didn't. I used my ETX on the same objects to see if I saw the same problem, suggesting was my eyes -- it wasn't. This left me with the conclusion that my Newtonian's primary mirror may have astigmatism.

A bit of reading told me that it was possible that I still had an alignment problem, though I'd tried very hard to get the collimation right. 

I'd used a homemade Cheshire eyepiece to help me get it right. As the animation at left shows, I tried to adjust the secondary to put the dot I'd painted on the center of my primary, right on the cross hairs. Then, of course, I aligned the primary to get the reflected cross hair coincident with the centered primary dot.

Even so, I wanted to be certain about the alignment, because it had been a difficult procedure due to the short focus of the telescope. Buying a new primary mirror would have been expensive, and I didn't want to do that on incomplete evidence. So for much less than the cost of a new primary, I bought a Celestron Collimation Eyepiece to more precisely adjust my telescope's collimation.

Best  thing I've ever done. I found, using the Celestron device, that I'd been more often than not getting the secondary alignment wrong. My homemade Cheshire device was too short to reveal the error. The poor secondary alignment was causing the apparent astigmatism. Now, with the better alignment, the astigmatism was gone, and views were crisp. I checked the system critically on some close doubles, and things looked nearly textbook.

The bottom line is, if you have a Newtonian reflector -- especially a short focus one -- don't do as I did and just assume that you've got the knack for optical alignment. It's not that expensive to get a Collimation Eyepiece, or for a bit more money a laser collimator, like the Orion LaserMate Deluxe II Telescope Laser Collimator. You, like me, may be surprised that your skills aren't as good as you thought. I figure that over the years, probably 80% of the time my reflectors have been misaligned enough to cause some degradation of performance.

So don't agonize over or tolerate poor telescope performance. Get your collimation eyepiece in hand, go to the Newtonian Collimation Tutorial, review the material, and get your Newtonian performing like it should. 

Sunday, February 17, 2013

Hello Spring Moon

Lunar Stofler Region - ETX90 Photo
Well, the winter of 2013 is easing off, so I'm getting mentally prepared for another observing season. I know -- if I wasn't so frail of spirit, I'd have observed through the winter on nearly every possible occasion. But I just couldn't get worked up to brave the cold this year.

I'll start lightly, by observing one of my favorites, the moon. I love looking at the ever changing views of the craters, like those of this photo from my ETX 90 photos page. The lighting variations of the countless craters bring up fantastic details each time I look. But this year will be special, at least for me. We just lost one of my most admired space pioneers in 2012, that being Neil Armstrong, the first man to set foot on the moon. He along with Buzz Aldrin and Michael Collins were the courageous astronauts that rode Apollo 11 all the way to the moon, with Armstrong and Aldrin descending to the lunar surface.

If you're old enough, you likely remember where you were and what you were doing on that momentous occasion. I remember precisely what I was doing. I had just graduated college with my science degree, and was thinking what a lucky break it was that just as I was poised to begin my career, we were landing on the moon. I thought my science future looked exceedingly bright.  Ah, the lamenting of youth.

My parents only had the one TV, and it was black and white at that. But they knew how much the moon landing meant to me, having bought me telescopes and astronomy books since my grade school days. So they let me watch the entire landing broadcast. I was glued to the set, and took a few Polaroids of the TV screen as history unfolded.  I'll never forget it -- it was one of the biggest thrills of my life.

I don't think I'll be able to look at the moon again, now that we're moving past that exciting era, without thinking of Neil Armstrong and his crew.  Those memories will definitely heighten my excitement each time I take on the wonders of our nearest neighbor, whether it be with my modest 60mm telescopes, or my six inch reflectors.

If you haven't looked at the moon in awhile, I suggest you study up a bit on the Apollo 11 mission and the excitement it caused, then see if you aren't a bit more inspired to get out there and give your eyes the unparalleled treat of the moons mountain ranges, craters, mare, rilles, and shadows. You can start that study of Apollo 11 with the following excellent book:
Moonshot: The Flight of Apollo 11 (Richard Jackson Books (Atheneum Hardcover))