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Brass Unitron 102mm F15 OTA

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#26 Terra Nova

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Posted 28 March 2021 - 03:41 PM

That's what I'm referring to.  The black material wasn't paper, but it looked like paper -- the 2 mount bolts held them in place.

 

I removed the bolts on mine for standard tube rings; then, I flocked to keep the tubes positioned.

Mine was the same, with the mounting bolts removed (I also used rings), the cylinders would slide. I held mine in place with mounting tape, fore and aft.


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#27 starman876

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Posted 28 March 2021 - 04:22 PM

When I redid the baffle in the 80mm f15 Jaegers, I used the technique of mounting the rings on thin dowels and sliding the whole assembly into the tube. The rings were made from thin plywood, like you can get at craft and hobby shops. The smaller holes were cut with a hole saw. For the largest, I drilled a series of holes, then carefully cut between them with a razor blade. Lined them all up and drilled three holes through all of them, near the edge, for the dowels, then glued it up with the proper spacing. It ended up a tiny bit warped, which gave it enough tension in the tube to stay in place. 

 

For the 6"f9, I'm planning to add some baffles this spring. It only came with two in the middle, each about 1/4" thick, doing double duty as baffles and reinforcement of the tube against pressure from the rings.

 

I have some 1/16" aluminum sheet, and plan to cut the holes with a fly cutter. At this point, I think I will cut the outside circumference with the bandsaw. I could directly glue them in place with JB Weld. But have been playing with the idea of making three small tabs on each, that bend at 90*. I would over-bend them in a bit for test fitting, then bend them out a bit to provide a little pressure for final placement. A dab of silicone glue under each would hold them. What I like about this is that if the rings are a hair under-sized, they will still have some mechanical force keeping them in place, and the tabs can flex with expansion and contraction. It would also be fairly easy to reverse. 

 

For the Jaegers, there was no way to reach into the tube. The 6" has a 7" tube, so it's easy to get into. A 4" tube would be a close call for one way or the other. 

 

Chip W. 

I could just stick a regular 152 unitron tube inside of it.  Just thinking out loud here.



#28 starman876

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Posted 28 March 2021 - 04:23 PM

The 4” Edmund F15 refractors used card of baffles held in place by slide-in cardboard cylinders.

card board?   Never seen that before.



#29 starman876

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Posted 28 March 2021 - 04:24 PM

I'm gonna use the Edmund Method on my Jaegers 50:  cardboard tubes with black paper glued to the ends.

 

If I had your Unitron, I would have a local shop make a brass set -- thin sheet metal that the shop can punch-cut (disks with 4 tabs) with simple hole diameters (no 27.82mm stuff).

brass sounds interesting.


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#30 Bomber Bob

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Posted 28 March 2021 - 05:56 PM

brass sounds interesting.

I don't think it would be too expensive - if the brass is thin, and the design is simple.  Some of the cheaper Japanese fracs I've worked on used very thin tin.



#31 oldmanastro

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Posted 28 March 2021 - 06:52 PM

What a wonderful and unique Unitron telescope. Congratulations on this acquisition. I think that the best word to describe this telescope is awesome.



#32 starman876

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Posted 28 March 2021 - 08:07 PM

What a wonderful and unique Unitron telescope. Congratulations on this acquisition. I think that the best word to describe this telescope is awesome.

Thank You



#33 ccwemyss

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Posted 28 March 2021 - 09:16 PM

I could have just as easily ordered thin brass from Online Metals, but since the AP has an aluminum tube, I wanted to match with it for similar expansion. It's also less weight.

 

There is someone on the classifieds who seems to be 3-D printing aperture masks for refractors - you specify the diameter of the rim and the hole. You could probably get them to make a set to your specifications and just slide them in, followed by a couple dots of superglue (after applying some of your magic black paint). I was thinking of contacting them to see if they could make a new dew shield cap for my 142.

 

I just ordered a bottle of Black 3.0 today to try on the inside of the AP.

 

Chip W.


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#34 starman876

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Posted 29 March 2021 - 06:57 AM

I could have just as easily ordered thin brass from Online Metals, but since the AP has an aluminum tube, I wanted to match with it for similar expansion. It's also less weight.

 

There is someone on the classifieds who seems to be 3-D printing aperture masks for refractors - you specify the diameter of the rim and the hole. You could probably get them to make a set to your specifications and just slide them in, followed by a couple dots of superglue (after applying some of your magic black paint). I was thinking of contacting them to see if they could make a new dew shield cap for my 142.

 

I just ordered a bottle of Black 3.0 today to try on the inside of the AP.

 

Chip W.

I read that Black 3.0 will not last long.  It is meant for a controlled environment.  Last thing I want is to have to figure out a way to get flaking paint from inside a tube.


Edited by starman876, 29 March 2021 - 06:58 AM.

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#35 PawPaw

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Posted 29 March 2021 - 08:48 AM

Terra Nova, on 28 Mar 2021 - 2:51 PM, said:

The 4” Edmund F15 refractors used card of baffles held in place by slide-in cardboard cylinders.

 

 

card board?   Never seen that before.

 

The cardboard baffles in my circa 1957 Edmund 4" has flock paper glued on the inside of the baffles.  As you can see by the pics they slide snugly inside the aluminum tubing.  The flocking is velvet-like and according to Edmunds ads provide millions of light traps and is superior to black paint. 

 

Don

 

 

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#36 Bomber Bob

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Posted 29 March 2021 - 09:02 AM

AHEM, like I said back on Post #23:  I'm gonna use the Edmund Method on my Jaegers 50:  cardboard tubes with black paper glued to the ends.


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#37 starman876

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Posted 29 March 2021 - 11:26 AM

Terra Nova, on 28 Mar 2021 - 2:51 PM, said:

The 4” Edmund F15 refractors used card of baffles held in place by slide-in cardboard cylinders.

 

 

card board?   Never seen that before.

 

The cardboard baffles in my circa 1957 Edmund 4" has flock paper glued on the inside of the baffles.  As you can see by the pics they slide snugly inside the aluminum tubing.  The flocking is velvet-like and according to Edmunds ads provide millions of light traps and is superior to black paint. 

 

Don

Interesting



#38 semlin

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Posted 29 March 2021 - 01:13 PM

if you use cardboard then, depending on how precise you want to be, a circular mat cutter could help.  these are normally used for making painting and photo frame mats.  i would tend to double or triple up cardboard for this application you could probably also cut doorskin veneer with this with a lot of passes.  here is an inexpensive cutter but there are cheaper ones on amazon.  olfa is a good company.  

 

 

https://www.amazon.c...17041157&sr=8-7


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#39 starman876

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Posted 29 March 2021 - 03:31 PM

if you use cardboard then, depending on how precise you want to be, a circular mat cutter could help.  these are normally used for making painting and photo frame mats.  i would tend to double or triple up cardboard for this application you could probably also cut doorskin veneer with this with a lot of passes.  here is an inexpensive cutter but there are cheaper ones on amazon.  olfa is a good company.  

 

 

https://www.amazon.c...17041157&sr=8-7

all kinds of good information.  Thanks



#40 Terra Nova

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Posted 30 March 2021 - 12:21 PM

if you use cardboard then, depending on how precise you want to be, a circular mat cutter could help.  these are normally used for making painting and photo frame mats.  i would tend to double or triple up cardboard for this application you could probably also cut doorskin veneer with this with a lot of passes.  here is an inexpensive cutter but there are cheaper ones on amazon.  olfa is a good company.  

 

 

https://www.amazon.c...17041157&sr=8-7

I think black foam-core might work very well also. I really like working with foam-core. It’s easy to cut precisely with an X-acto knife, and it’s lightweights and durable.



#41 Ken Launie

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Posted 30 March 2021 - 01:13 PM

Ideally baffles should have a knife edge to maximize contrast. Any thickness results in a surface that is parallel to the light beam, and rays at the edge of the field just bounce toward the eyepiece. The Clarks used strips of thin sheet metal that were bent at 90 degrees long ways, and cut with tin snips on one side up to the bend. The entire strip was then rolled up, painted flat black and shoved it with a long dowel or board to the appropriate position down the tube. The springiness of the metal created a force that held it in position. Simple and easy to do, and no gluing or screws needed. To size them, make a scale drawing with the objective's aperture at one end and the inside diameter of the focus tube at the other. Make the height of the tabs at each baffle position just touch the rays. Here's a quick snapshot of an example out of the tube that came from the Clark factory.

--Ken

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#42 semlin

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Posted 30 March 2021 - 01:40 PM

Ideally baffles should have a knife edge to maximize contrast. Any thickness results in a surface that is parallel to the light beam, and rays at the edge of the field just bounce toward the eyepiece. The Clarks used strips of thin sheet metal that were bent at 90 degrees long ways, and cut with tin snips on one side up to the bend. The entire strip was then rolled up, painted flat black and shoved it with a long dowel or board to the appropriate position down the tube. The springiness of the metal created a force that held it in position. Simple and easy to do, and no gluing or screws needed. To size them, make a scale drawing with the objective's aperture at one end and the inside diameter of the focus tube at the other. Make the height of the tabs at each baffle position just touch the rays. Here's a quick snapshot of an example out of the tube that came from the Clark factory.

--Ken

 

that's a good solution.  you need to keep the cuts the same length and distance apart and use as many cuts as you can manage to get a good circle.

 

the camera lens crowd believe an aperture needs be as round as possible, which is why better camera lens designs use more plates for the iris diaphragm that adjusts the aperture.

 

.



#43 starman876

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Posted 30 March 2021 - 03:25 PM

Ideally baffles should have a knife edge to maximize contrast. Any thickness results in a surface that is parallel to the light beam, and rays at the edge of the field just bounce toward the eyepiece. The Clarks used strips of thin sheet metal that were bent at 90 degrees long ways, and cut with tin snips on one side up to the bend. The entire strip was then rolled up, painted flat black and shoved it with a long dowel or board to the appropriate position down the tube. The springiness of the metal created a force that held it in position. Simple and easy to do, and no gluing or screws needed. To size them, make a scale drawing with the objective's aperture at one end and the inside diameter of the focus tube at the other. Make the height of the tabs at each baffle position just touch the rays. Here's a quick snapshot of an example out of the tube that came from the Clark factory.

--Ken

Thanks Ken. More good informationwaytogo.gif



#44 Terra Nova

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Posted 30 March 2021 - 04:19 PM

Ideally baffles should have a knife edge to maximize contrast. Any thickness results in a surface that is parallel to the light beam, and rays at the edge of the field just bounce toward the eyepiece. The Clarks used strips of thin sheet metal that were bent at 90 degrees long ways, and cut with tin snips on one side up to the bend. The entire strip was then rolled up, painted flat black and shoved it with a long dowel or board to the appropriate position down the tube. The springiness of the metal created a force that held it in position. Simple and easy to do, and no gluing or screws needed. To size them, make a scale drawing with the objective's aperture at one end and the inside diameter of the focus tube at the other. Make the height of the tabs at each baffle position just touch the rays. Here's a quick snapshot of an example out of the tube that came from the Clark factory.

--Ken

Well chalk off the foam-core idea then. Oh well.


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#45 starman876

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Posted 30 March 2021 - 04:36 PM

Well chalk off the foam-core idea then. Oh well.

waytogo.gif



#46 Terra Nova

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Posted 30 March 2021 - 06:34 PM

Interestingly, there was a discussion concerning baffling here on CN fourteen years ago and another person suggested foam-core (post #2):

 

https://www.cloudyni...ast-and-easily/

 

Actually, if you peruse the ATM forum posts, you will see the application of various materials from 1/8 to 1/4 inch thick, plastic sheets, plywood, foam-core, etc. being employed in the production of baffles that are considerably thicker than a knife blade.

 

https://www.cloudyni...ast-and-easily/

 

https://www.cloudyni...s#entry10904331

 

I know, I know, just because someone else does it, it doesn’t make it right. (Ward Cleaver said that (more or less). :lol: )

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Edited by Terra Nova, 30 March 2021 - 06:51 PM.


#47 starman876

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Posted 30 March 2021 - 08:52 PM

I will stick to the thin metal baffles.  Every high end scope I have read about always talks about the knife edge baffles 


Edited by starman876, 30 March 2021 - 08:52 PM.

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#48 luxo II

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Posted 31 March 2021 - 05:56 AM

Only in the USA. 
 

If I had migrated decades ago I’d have a “travelscope” in the form of a Perkin Elmer 30” cassegrain on a trailer and the truck to pull it, a backyard obsy decked out with a couple of Unitrons and a decent Zeiss or two as guidescopes for a Santel 16” maksutov, a Boller & Chivens 16”  and a Clark 10” out the back someplace.

 

Green with envy. If only someone here had gear like that.


Edited by luxo II, 31 March 2021 - 06:04 AM.


#49 starman876

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Posted 31 March 2021 - 07:20 AM

Only in the USA. 
 

If I had migrated decades ago I’d have a “travelscope” in the form of a Perkin Elmer 30” cassegrain on a trailer and the truck to pull it, a backyard obsy decked out with a couple of Unitrons and a decent Zeiss or two as guidescopes for a Santel 16” maksutov, a Boller & Chivens 16”  and a Clark 10” out the back someplace.

 

Green with envy. If only someone here had gear like that.

sounds reasonable



#50 Terra Nova

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Posted 31 March 2021 - 09:03 AM

I will stick to the thin metal baffles.  Every high end scope I have read about always talks about the knife edge baffles 

I find it quite odd that it didn’t have baffles to begin with.




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