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.

Bummer!

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.