A Tale of Two Duetrons



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Here are pictures of a couple of Duetrons.  A  Duetron is a device that allows two people to look through the same telescope at the same time. It was an accessory available from the Unitron company for many years during the 1950′s through the 90′s. The most common version was designed for .965″ eyepieces. A more rare version was designed for 1.25″ eyepieces. Here they are pictured next to each other. The one on the left in the bottom picture is the more common .965″ version. Note that the 1.25″ version is designed to go into a 1.25″ focuser while the .965″ was designed to fit into a Unitron draw tube.

Dave and Replica Alvan Clark

Alvan Clark Replica

I have always wanted to own an Alvan Clark telescope. Unfortunately they are beyond my range. So, when I recently completed my first lens, I decided to create a scratch-built mount and tube assembly to house it and I wanted the completed telescope to look a lot like an Alvan Clark. This 3 1/2″ f/15 telescope is not an attempt to create a perfect replica in all respects, though many features of the telescope are intended to be nearly identical to an Alvan Clark. Maybe it should be called an “Homage Alvan Clark Telescope”.

I made virtually everything you see in the picture. The only exceptions are some small screws and bolts and the finder lenses. It was a long and difficult process described on this page: Making The Alvan Clark Replica Telescope. This scope is certainly not an Alvan Clark but it looks great, works  well and I made it with my own hands.

To me the function of this telescope is of minor importance. This is more like a beautiful mechanical sculpture intended to have a permanent place in my living room or study.  Despite that, it would be offensive to me if this showpiece did not perform its basic duties under the night sky, and it does that well. When I am using this telescope it is easy to imagine that I have traveled back in time over 100 years.

I have made a couple of Youtube videos about the scope here:  Alvan Clark Replica Tour and Alvan Clark Replica Teardown


Vintage Classic “GOTO Kogaku” brand telescope

I recently posted a video of this beautiful 80mm “GOTO Kogaku” telescope.IMG_3399 small

The reason for the use of “GOTO Kogaku” (rather than simply “Goto” is to disambiguate this from the very common computerized “Go To” Telescopes that proliferate everywhere. There is no computer with this telescope other than the user’s brain. If you are searching for “GOTO” brand telescopes you may wish to try the term “GOTO Kogaku”.  The video is at http://youtu.be/uoQs326-h00 .

Please check it out!

Unitron Altaz Mounts

Take a look at this picture. Guess which Unitron altaz mount is biggerUnitron altaz mounts 3 small

They appear to be about the same size because, of course, I used a trick of perspective. The one on the left is for a three inch telescope and the one on the right is for a much larger 4 inch. I have often been confused by pictures of these mounts because it is nearly impossible to tell them apart without a sense of scale. Here are the same two mounts seen right next to each other. (Sorry, I switched them from left to right). You can now see that the mount for the 4 inch is much larger, more massive and stronger.Unitron altaz mounts 2 small

Here are three mounts next to each other. The one on the far left is for a 60mm scope, though I have seen three inch scopes mounted on it.Unitron 3 altaz mounts small

For more views of Unitron altaz mounts with their associated telescopes onboard please check out my YouTube Video at http://youtu.be/ETlMv-KLEVM .


Replica Antique Zeiss Mount

I recenlty purchased a beautiful Zeiss Starmor 60mm spotting scope from about 1918. The scope is in superb condition and works well.


Zeiss Starmor
Zeiss Starmor

The scope did not have any mount and I wanted to display it in my living room so I decided to use my metal working skills to make a replica of the original table-top mount for the scope.

Starmor Mount

So I started by cutting out a piece of 5/8 aluminum plate in the shape of the feet;

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Next, I cut a piece of aluminum tube to make the centerpost, flattened three sides of it in the mill and notched it for 1/4 inch bolts


I drilled and tapped each foot for 1/4 – 20 bolts to attach them to the center-post. Here it is all put together:


I did a lot of filing and shaping of the feet. The idea was to make it look like an antique single-piece casting. The 1/4 -20 bolts do the majority of the support work, but I used some JB Weld high strength epoxy at the joints to make sure nothing could move. I love that stuff! I also used some JB Weld Metal Putty to help fill in some smaller gaps and build up one of the legs where it was not quite symetrical with the others.


Next it was time for some quick work with Bondo automotive metal filler. This stuff sets so fast you barely have time to get it in place. Luckily it files and sands off very easily. Note, the Bondo is not structural in this piece. It is just meant to make the item look more like a casting.


Next came some easy sanding and shaping. It was a piece of cake compared to the raw aluminum in the legs.

I turned a piece of 5/8 Stainless Steel to fit the scope, threaded the other end and turned an aluminum plug. The plug is held in with three small screws through the tube, then the shaft is bolted in. I wanted to make this easy to change should I want a taller mount or maybe want to use the scope on a tripod. I would be easy to adapt the Stainles Steel pinion shaft to most anything.


This is the final product. It looks very appropriate with the scope. It is very nice to have a lathe and mill to make things like this.


Pictures of the original are here: Zeiss Historica (second image down).

Removing the counterweight from a Meade 7 inch Maksutov

Optics from my Meade 7 inch Maksutov

Optics from my Meade 7 inch Maksutov

Recently I began to notice some disturbing loud clunking noises when I moved my Meade 7 inch from one position to another. I was already aware that this scope contained a substantial counterweight inside the tube. The counterweight allows the telescope to balance in fork arms designed for a shorter 8 inch Schmidt Cassegrain telescope. The counterweight was loose inside the tube, bouncing up against the delicate primary mirror! Sooner or later a disaster was inevitable. It had to go. Even if the weight had still been well attached, it would be desirable to remove it. The counterweight causes slowed cooling resulting in problems with the image under less than ideal circumstances. Some ATMs have already removed the weight for that reason alone. See the excellent information from Steve Hollenbach at http://www.astromart.com/articles/article.asp?article_id=685 . His advice and instructions are invaluable!

It was time for major surgery on that telescope. This is not something I recommend for all owners of the Mead 7 Mak. I undertook this with some trepidation and I am a highly experienced Amateur Telescope Maker. You might need to cut your tube or pry the counterweight out of the back of the tube using some sort of crowbar. You could easily drop the mirror inside the tube while in the process of disconnecting the focusing mechanism, damage the mirror while handling it inside the tube, drop the meniscus corrector plate, break the baffling tube, get dirt or metal particles into the grease on the mounting tube or any number of other possible disasters. Consider the risks before you do this yourself!

I could easily have ruined the scope. But, instead, I got lucky. Here is the result:

Mead 7 inch Mak with new balance point

Mead 7 inch Mak with new balance point

Please see my Youtube video at http://youtu.be/nLqaeY7h7k8 for all the details.

The Result

I had a three scope shootout on 3-5-14. Jupiter was near the zenith and the seeing was very good for Colorado. Here is a picture:

Scope Shootout 3-5-14

Scope Shootout 3-5-14

The “new” Mak is at the far left, then a 6 inch f/15 folded Jaegers achromat, then a Meade 5 inch ED APO at the far right. I was glad to see that the new, lighter mount for the Mak was sufficient for visual observations up to over 200x. The Mak cooled very nicely and what was nifty was that it stayed cool. I have noticed in the past that the scope would look great momentarily but it never really settled down. It was very tempramental and it would shine briefly only to dissapoint a moment later. I hypothesize that this was due to the large thermal inertia of the massive counterweight. Anyway, that behaviour was gone tonight. Hurray! The thermal effects in the Mak have vanished. It still has a relatively large central obstruction, though so putting it up against a couple of smaller refractors is a fair competition.

The optics in these scopes are all nearly perfect. The ED APO is superb. The 6 inch is great but there are a lot of optical surfaces in that scope so it is a little softer. The Mak shows a textbook diffraction pattern inside and outside focus.

So which one is best?

The Mak has a perfect image during the brief moments of perfect air, a few times every several seconds. But, even with the dramatic improvement, it is a bit more susceptible to seeing than the other scopes. The smaller APO is more steady, and the image is nearly as good as its big brother. The six inch is a great big horse compared to these two. The image is lovely but it does not justify the extra effort to set it up. So the little APO wins for nights of poor or mediocre seeing. The Mak wins for nights of good or great seeing. Both of these scopes are simple and easy to use, especially now that the Mak has lost all that weight.

I am very happy with the outcome!


Completely Baffled!

Improved  baffling of the six inch folded refractor

In my design there is a bulkhead near the focuser. See Constructing a Folded Refractor. This is mostly for structural support of the tube. It increases the rigidity. But the baffling incorporated at that point is fairly ineffective. The geometry makes it nearly impossible to block stray light from the objective (like an off-axis street light) from entering the eyepiece. However, I was able to do a very effective job of baffling by making a stop that fits on the inside of the focuser tube. That is the way Unitron did it and it seems to work just fine.

Focuser Baffling

The focuser at the top of the picture is from a Unitron 131C, 75mm folded refractor. At the bottom is the draw tube from my scope. Notice that I have put a blackened light stop at the end of the draw tube. The size of the hole in my version is only 7/8 inch. This is just barely enough for full illumination at the center of my eyepiece. I am using the scope for planetary and lunar observation so this works well for me. I can easily enlarge the opening if necessary but the light fall-off at the edge of the field is not even noticeable. And stray light from my irritating street light is not a problem.

Uni-Clone 4 inch telescope mount


This is a Unitron 4 inch mount alongside a nearly identical home-built mount of unknown origin. The similarities between them are numerous. They both have the Unitron style declination slow motion controls, large high quality setting circles and are nearly identical in size and overall design. But the home-built mount actually has several improvements over the superb Unitron, including a breathtaking mechanical clock drive adjustment mechanism. The unknown maker of this mount was a genuine craftsman of the highest caliber. I call this mount a Uni-Clone with the greatest possible respect. You can see closeups of the mount, clock drive and corrector on Youtube at http://youtu.be/d1VNP8gpH-I .