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Jeff Morgan
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Reged: 09/28/03
Posts: 4018
Loc: Prescott, AZ
Folded Refractor First Light
      #1771693 - 08/11/07 03:37 PM Attachment (288 downloads)

Last night I had first light on the 4" f/13.5 folded refractor. Optically, I was very pleased with the performance. Epsilon Bootes and Epsilon Lyra split cleanly. The seeing was rather poor last night, so Jupiter didn't have much to offer.

Attachment

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1771704 - 08/11/07 03:41 PM Attachment (172 downloads)

Alignment of the mirrors was rather easy with a laser collimator. With the seeing, I did not want to tempt fate by attempting a lens collimation. Despite the fact that I disassembled the lens for a complete cleaning (it is purpostedly a 1950's vintage Unitron lens made under contract for the Navy), collimation was still very, very good. Star images were sharp at 168x and very good at 270x. There was just a slight displacement of the diffraction tings to the 10 o'clock position. But with the seeing, I was not 100% sure on that.

Attachment

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1771718 - 08/11/07 03:49 PM

Mechanically, I have a bit of work to do, and was hoping the CloudyNights ATM forum Brain Trust might have some comment.

The motions of the mount are very smooth. But there is a vibration/damping issue I need to nail down. Damping time is 5 seonds plus, and even a touch of the focser will induce vibration. Due to the stout construction elsewhere, I suspect the problem is in the pier legs. There are two possible issues:

1) The legs are removable. Note in the first picture that I use 1/4-20 hand knobs to attach each leg. There are simple holes in the wood, I did not use sleeve bearings. In the pier are 1/2" long steel threaded inserts. Should the legs be permanently attached? Or perhaps a different securing method?

2) I used 1/2" baltic birch strips for the legs, about 3" wide. Material was added to create an "I" beam section, but I could not do this full length. I'm about to start full scale production on my Dob, so I have lots of 3/4" bb stock on hand. My think was to glue sections to create a 1-1/2" thick leg section.

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Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Terry1229
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1771791 - 08/11/07 04:41 PM

THAT is a great scope! for sharing...

--------------------
Terry:
A 6" f8 dob with 14mm Anteres eyepiece
Wixey
Homemade EQ & stepper
QC pro4000
spc900
homemade ele. focuser
New [used] Meade 8" sc ota
New [used]] CG5



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Wes James
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Re: Folded Refractor First Light new [Re: Terry1229]
      #1771874 - 08/11/07 05:46 PM

Beautiful worksmanship, Jeff- Looks like a scope to get a lot of pride & pleasure out of!
I would guess the vibration is coming from not only the feet, but the post as well. You didn't say what the center post was made of?? Baltic Birch seens to be a soft wood- and as such, not a lot of rigidity to offer. Kind of a tendency to "ring" (or maybe thunkkkk?). I would think if you can come up with a more stable mount, or add rigidity/density to what you have, you'll see an improvement in your dampening/stability.
Again- Beautiful job!

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Wes
Atlantic Beach, FL

Bino’s- Tak's, Fuji's, Nikon's, Canon IS and Garrett 20x110 Signature's,
Some telescopes from Carton & Zeiss 60mm's up through a couple of 8” reflectors… Orion 3.6" O/A- and a wonderful 4.25" Delmarva Schiefspiegler!
Some good friends, made here on C/N.
Oh- several cats and a wonderful wife!
Anyone want a cat???? :-O

"When your work speaks for itself- Don't Interrupt" -Gamble Rogers


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Wes James]
      #1771882 - 08/11/07 05:53 PM

Thanks Wes. The pier is a three-sided column 3/4" thickness baltic birch with caps on each end. I guess it could be replaced or filled with foam.

Originally I had thought about a tripod. The eyepiece position is fixed and closer in to the center, and it appeared in the original sketches that tripod legs and observer legs might interfere. I could always get some construction grade pine lumber and do a mock-up. However, I would prefer to track down other possibilities first.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Roy McCoy
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1771935 - 08/11/07 06:40 PM

Jeff,

That is really nice.

I've always wanted a scope with the eyepiece coming out the side like that. Is it comfortable to view through?

As for the vibration, could some be coming from the fork? If you removed the fork, clamped it to a table or something solid and the vibration changes then you'd get an idea of how much is the leg and how much is the fork.

--------------------
AstroTech 106
'86 Christen triplet 6"f/8


Edited by Roy McCoy (08/11/07 06:41 PM)


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Wes James
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Re: Folded Refractor First Light new [Re: Roy McCoy]
      #1771952 - 08/11/07 07:01 PM

Jeff-
I don't think filling your column with foam would do you any good... however, I would think filling it with sand would probably give you a good reduction in vibration??? Is that an option- or would the legs support that??? Another thing that might help if you were to attach the 3 legs to a piece of plywood- so the ends were firmly attached, or some kind of struts between the 3 legs to solidify them.
Wes


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Roy McCoy]
      #1772081 - 08/11/07 09:00 PM

Thanks Roy. Yes! It was *very* comfortable for observing last night! I had the finderscope oriented to the side, thinking I could also use it from the seated position. That did not work as I had to stretch up out of the chair. So, I changed the finderscope orientation so the eyepiece is at a right angle to the light path. This means I will have to use the finder from behind, which is also how I use the Telrad. I'll just set up my chart table behind the scope, then move to the chair when I get to the area I want.

I like your idea of testing the fork. I think I could secure it to the cast iron table on my table saw.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Wes James]
      #1772088 - 08/11/07 09:05 PM

Using sand could work, I'll priortize that one behind legs and testing the fork. The pier/leg combo is relatively light right now. Most of the mass is in the tube assembly. One of the mods I have planned for later in the week is to shorten the tube. It is about 4 inches longer than required. I wanted the margin in case my focal length measurements were off, but I hit the measurements dead on. The shortening operation will take around 4-5 pounds of load off the mount (front wood plus rear counterweight).

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Sid-W
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1772203 - 08/11/07 10:28 PM

That's a great design Jeff, I'm finding my 5 inch F10 refractor mounted on an EQ-5 quite hard to live with and it doesn't get as much use as it deserves. I have a few mobility problems as the result of a motorbike accident and quite often it is downright painful to get to the eyepiece.

I'm now going to think hard about folding it, once I have my current 'quick look' refractor project completed.

--------------------
127mm F10 generic Chi-Com refractor
Any amount of unfinished projects from the Wile E Coyote school of amateur telescope making


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Sid-W]
      #1773905 - 08/12/07 10:13 PM

Sid,

The project was not as difficult as one might think, and I would encourage you to try. (Just don't throw away the old tube )

There are many ways you can do this. In the models I drew up, shorter focal ratios are a bit easier. I would say think pretty hard about limiting yourself to two reflections (counting any diagonal). Also, when you do the layouts don't think like a Newtonian owner. That is to say, since the mirrors don't obstruct your light path think about oversizing each mirror. This will ensure that the image is formed on the flatest part of the flat. Flats are like any other optic, the edges are where most of the deviations are. So if you have a 1/10th wave flat, you can pretty safely assume the inner 90% is fantastically flat.

The other tip I would offer - forget about the old school concept of keeping the reflection angles as small as possible. If you do this, you end up with the "N" configuration. Fine, you kept angle of incidence errors small - until you add the star diagonal. You see, the "N" configuration still places the eyepiece at the end of the tube, just like a conventional refractor. And lets face it, virtually no one uses a refractor without a star diagonal. So, the "N" configuration with a star diagonal still has a total *system* angle of incidence of 45 degrees (90 degree total bend of the light path).

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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mattyfatz
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1773931 - 08/12/07 10:33 PM

Jeff,
That is a very nice scope. I especially like the fact that the eyepiece is always in the same spot.

--------------------
**Matty**
Stimulating the economy, one piece of equipment at a time.


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rboe



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Re: Folded Refractor First Light new [Re: mattyfatz]
      #1773968 - 08/12/07 10:54 PM

Jeff; I strongly suspect a small base for the forks to mount on. If you made the disc the same diameter as the width of the forks this would take advantage of the natural stiffness the forks provide.

In turn you will need to add some bracing from the larger base to the pier post to stiffen this wider base. Double thick BB for the base would be a good idea too.

Otherwise every thing else seems to be sized very well. Nicely done. I was up in Sedona on Saturday, I would have swung over if I had known you were in town.

--------------------
Ron


NS11GPS
Pronto
16" dob
127mm F9 Surplus Shed/Crawmach kit scope
Coronado SolarMax 40 on a Celestron 102 Wide Field



Best of ATM


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Sid-W
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Re: Folded Refractor First Light new [Re: rboe]
      #1775445 - 08/13/07 07:26 PM

Cheers for the advice Jeff

--------------------
127mm F10 generic Chi-Com refractor
Any amount of unfinished projects from the Wile E Coyote school of amateur telescope making


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: rboe]
      #1776156 - 08/14/07 01:19 AM

Thanks Ron. I have been thinking about enlarging that base too. I have gotten some very good ideas from folks, including the idea of using stringers from the feet to the top of the pier. Definitely have a hieracrchy of ideas here.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1777718 - 08/14/07 08:12 PM

Hi Jeff!

I'm intrigued by the telescope. Might you please post a simple diagram of the light path?

Thanks

Art

PS: Just returned from Stellafane in Springfield, Vermont. Was pleased to learn that they have an active hard surfaced runway, 5500 feet long.

Just in case you can't let go of the tow plane!


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1779814 - 08/15/07 07:23 PM Attachment (203 downloads)

The attached document is MS Word. It uses 2.14" and 1.5" quartz flats from ProtoStar. Each angle of incidence is 22.5 degrees, which offers the minimum angle of incidence errors for a two mirror system. It also renders a 90 degree eyepiece orientation.

I could have elected for a more Newtonian eyepiece position and had a more balanced scope. The trade off was a larger angle of incidence on mirror #2 and loss of the fixed eyepiece orientation. Of course, fixed eyepiece position was the original motivation for the project.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1779903 - 08/15/07 08:08 PM Attachment (85 downloads)

Thanks Jeff. I've a refractor in the works and am tempted to use at least one diagonal in it.

It uses lightweight, Schedule 20 PVC plumbing

Art

Attachment


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1781469 - 08/16/07 04:25 PM

That is an interesting concept Art - I think I have seen a couple of photos of a completed example here on CN. It might have been over in the Refractors forum, I'm not sure. The guy who built it was quite pleased with the result.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Ed Jones
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1783839 - 08/17/07 06:56 PM Attachment (167 downloads)

My 50 mm woody finder is a folded refractor. It's only 4 inches long and weighs only as much as a couple of 1.25 eyepieces. It works so well I've ordered another objective from SS to make another.

Attachment

--------------------
Ed Jones




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Chriske
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1784630 - 08/18/07 08:38 AM

Quote:

My 50 mm woody finder is a folded refractor. It's only 4 inches long and weighs only as much as a couple of 1.25 eyepieces. It works so well I've ordered another objective from SS to make another.




That is not only a optical thing, it's a piece of art to..
How many mirrors are there involved .? 2 ..?

--------------------
Chris



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Art Bianconi
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1784645 - 08/18/07 08:50 AM

Ed Jones wrote: My 50 mm woody finder is a folded refractor.

Ed you have a way of blowing peoples minds with the simplest of "toys".

This year I spent some time with friends at Stellafane. one of them, Dave Britz, entertained crowds with a small device that was nothing more than a shallow convex-Plano lens, and a mirrored flat on a 2 axis gimbal, all fixtured to a short piece of wood on a tripod.

He aimed the mirror in such a way as to reflect the sun's image through the lens and onto a large sheet of white, foam cored construction cardboard (Staples).

Next thing you know we are looking at a bright two foot diameter image of the sun, sunspots and all, and safe!

"I love it! Where did you get this thing!"

"The name and address are on the board"

Ed, why didn't you tell us?!


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1785280 - 08/18/07 04:08 PM

Thats interesting! Are the lenses you ordered to scale it up?

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Ed Jones
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1785314 - 08/18/07 04:29 PM

Hi Art!
Well you exaggerate a little, the image is 8 or 9 inches, not 2 feet but it is never fails to amaze people how such a simple thing can produce such a nice looking big solar image. You're talking about my solar projector. You can see it on my web site: http://home.isoc.net/%7Eejones/
I make the lenses and sell them, mostly to schools.

Jeff, I'm going to make another one just like this one for another scope.

--------------------
Ed Jones




Edited by Ed Jones (08/18/07 04:31 PM)


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1785470 - 08/18/07 06:06 PM

Ed wrote: ". . . . the image is 8 or 9 inches, not 2 feet"

I was about 80 feet away aiming the mirror, give or take a half dozen bottles of beer!

At that distance, everything was starting to look bigger and better!

Art


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Ed Jones
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1786367 - 08/19/07 09:19 AM

You'ld make a good fisherman, "The one that got away was at least 2 feet!"
You know the lens is only a plano-convex but you don't see any color since it's at about f/250.

I forgot Chris, yes there are 2 mirrors.

--------------------
Ed Jones




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Chriske
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1786390 - 08/19/07 09:36 AM

Quote:



I forgot Chris, yes there are 2 mirrors.




A while ago I made a folded refractor (drumscope) myself. Almost got nuts collimating it's 4 flats. My friends say it's still visible...

--------------------
Chris



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rboe



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Re: Folded Refractor First Light new [Re: Chriske]
      #1786579 - 08/19/07 12:03 PM

With friends like that......

--------------------
Ron


NS11GPS
Pronto
16" dob
127mm F9 Surplus Shed/Crawmach kit scope
Coronado SolarMax 40 on a Celestron 102 Wide Field



Best of ATM


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Chriske
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Re: Folded Refractor First Light new [Re: rboe]
      #1786590 - 08/19/07 12:10 PM

Quote:

With friends like that......




I'm not going to reply on this one, some of them read this section......

--------------------
Chris



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rboe



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Re: Folded Refractor First Light new [Re: Chriske]
      #1786598 - 08/19/07 12:16 PM

Rats!

Jeff; have you had a chance to chase down the shakes or attempt a solution yet?

--------------------
Ron


NS11GPS
Pronto
16" dob
127mm F9 Surplus Shed/Crawmach kit scope
Coronado SolarMax 40 on a Celestron 102 Wide Field



Best of ATM


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Jeff Morgan
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Reged: 09/28/03
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Re: Folded Refractor First Light new [Re: rboe]
      #1787077 - 08/19/07 04:21 PM

No. I've spent most of this weekend working on the Newtonian, I still need to get some turnbuckles. I spoke with an engineer friend, he said that what make a large difference. (Hopefully, enough.)

Even so, we took the refractor out last night despite the springiness. Just after sunset I was pretty sure I split Antares. I asked Jo Ann (my astro-novice girlfriend) if she saw anything "unusual". She also picked up the companion, same location and color I saw. The collimation still needs a tweak, put that old lens can perform. Also had some great views of the moon: Theophilus crater, Moltke, Rimae Hypatia (all on Rukl chart 46). Jupiter didn't offer too much, but it was right over the house. The ET cluster (NGC 457) looked good. Also saw Nu Cass. Not a very hard double by any means, but very pretty. I liked it much better than Alpha Cass.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1787124 - 08/19/07 04:55 PM

Ed wrote: "My 50 mm woody finder is a folded refractor"

Ed, I am always looking for projects that are affordable and build-able by young hands with little adult supervision.

Are there plans available for this handsome little reflecting refractor?

I've a 110mm Jaeger achromat collecting dust, along with some other, smaller lenses that were considered for a Ross Null tester and I'd enjoy finding a home for them.

Thanks

Art


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Ed Jones
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1787276 - 08/19/07 06:21 PM Attachment (117 downloads)

Art,
No I don't have any drawings, I'm not a CAD person yet. In any case a drawing would be good for only one focal length lens and one thickness mirror. The way I did it was simple, crude but effective. First I drew a scale drawing of the lens, it's BFL to the diameter of the field of the eyepiece on a piece of paper and cut it out with sissors like this:

Attachment

--------------------
Ed Jones




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Ed Jones
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1787329 - 08/19/07 06:42 PM Attachment (114 downloads)

Next I looped the paper over at a 90 degree angle, pressed it down and made two neat fold creases in the paper. The folds are where the mirrors will be. I laid this folded optical layout on another piece of paper and traced along the folds where the mirrors go, drew parallel lines for the thickness of the mirrors, thickness of the double sided tape I used to hold the mirrors and parallel lines for the 1/4 inch plywood. This gave me the dimension of the sides and walls. I used a hole cutter for the objective and eyepiece. I used 4 small blocks of wood to hold the objective. When you glue the walls up you need to be sure they are square. Crude yes but was fairly easy to do. You CAD guys can have fun with this one.

Attachment

--------------------
Ed Jones




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Ed Jones
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1787344 - 08/19/07 06:46 PM Attachment (123 downloads)

Here's a shot with the top plate off:

Attachment

--------------------
Ed Jones




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Art Bianconi
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1787346 - 08/19/07 06:46 PM

Thanks Ed.

Did you fold the paper to different angles to get the mirror planes, spatial relationships and distances?

Is it necessary for the the angles of the two mirrors to be the same?

Is it necessary for the mirrors to be optical flats? Did you use elliptical secondaries?

How did you micro adjust the mirror angles to collimate the light path?

Is the lens fixed in place?

Thanks!

I'm gonna build one!

Art

EDIT: Your two additional posts showed up while I was creating this one! Thanks



Edited by Art Bianconi (08/19/07 06:49 PM)


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1787386 - 08/19/07 07:06 PM

Quote:

I'm gonna build one!




You know, I might too! When I first looked at folding, I was thinking the short(er) focal ratios could be a problem. But this possibility did not occur to me. It arrives at my preferred 90 degree orientation and uses only two mirrors. And it would be sooo easy to mount.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Ed Jones
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1787388 - 08/19/07 07:06 PM

Did you fold the paper to different angles to get the mirror planes, spatial relationships and distances?
No I positioned the objective and final focus position then squished the paper and pressed the folds.
Is it necessary for the the angles of the two mirrors to be the same?
No but it looks nice if they are.
Is it necessary for the mirrors to be optical flats? Did you use elliptical secondaries?
Well this was just a finder so I suppose they don't have to be super flat. I think mine were <1/2 wave however. If you use high power then they should be good.
How did you micro adjust the mirror angles to collimate the light path?
Well again this is just a finder, I relied on accurate woodworking and square sides. I did drill the eyepiece hole last with everything assembled making sure the pupil was in the right location.
Is the lens fixed in place?
Yes no adjustment. It was a binocular lens as is the eyepiece and there is a lot of aberration at the edge of the field.

--------------------
Ed Jones




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Art Bianconi
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1789265 - 08/20/07 04:24 PM

Just got an E-Mail from SS acknowledging my order.


Item Quantity Price Total
SKU: L2160D
68MM DIA OBJECTIVE LENS, 360MM FL $29.50

SKU: PM1170
PRECISION 50MM DIAMETER LEBG 1/10TH WAVE ALUMINIZED MIRROR 2 @ 14.00 $28.00
Sub Total: 57.50
Tax: 0.00
Shipping: 0.00
Less 10% member discount $5.75
Total: $ 51.75


I could have ordered a larger achromat but it wasn't cemented and I did not want to be bothered with buying and using Balsam.

I will be making the box using a layup of 4 ounce bidirectional fiberglass on one side of a 1/8" foam core and black satin finished Formica on the other (outer) surface.

This should prove good practice for a fork mount I am building where the same materials and technique are employed. Small strips of epoxy impregnated cloth will join the insides joints.

I'll model the parts and assembly in SolidWorks to get the geometry right then model my "virtual" "Reflecting Refractor".

Not sure yet if the mirrors are large enough to cover the conical sections where they will live. I may have to do some juggling of angles and distances to get them right. That's part of the fun.

This IS going to be fun!

Thanks Ed!

Art

Jeff: I will be making fully dimensioned, orthographic drawings and converting them to a neutral file format (PDF). If you want, send me your lens specs and I'll update the model and the drawings to match.

"Are we having fun yet?"


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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1794124 - 08/22/07 07:29 PM

Thanks Ed!

The lens and mirrors are here and I will be developing the enclosure this evening. If I can stay awake long enough, I'll try to provide rendered iamges, complete with light path.

Art


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1794481 - 08/22/07 10:31 PM

Art,

On the road for awhile. I'll email you the layout and dimensions next week.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1794496 - 08/22/07 10:35 PM

Ed I'm falling asleep and have little to show for my efforts.

Sometimes the simpler tool is the better one.

I got further along faster using a folded paper conical outline than I did with the engineering software!

Trying to fold a three segment optical path, adjust the angles and place two 50mm flats so they don't vignette and maintain the overall F/L was more than these tired eyes could manage with the software.

The difficult we do right away, the easy takes forever!

Why is that?!

Art


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Tom Dugan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1800439 - 08/25/07 09:26 PM

Art, I've got the same lens and mirrors on order and I've been thinking. ( Uh-oh!)

If you're tempted to use the Fuchs focuser on this little beast, the rods would penetrate into the light path if it's folded as in Ed's design. But that's no problem if instead of moving the eyepiece, you move the objective. Hmmm?

--------------------
Antares 10" Dob
Orion 150mm Mak
Orion 100mm EQ refractor
Homebuilt w/ Stellarvue 102D lens
Homebuilt w/ Antares 120 mm lens
Coulter 1st generation 13.1" mirror (waiting patiently)
Unknown number of binocs
Parts, parts, parts
More parts


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Re: Folded Refractor First Light new [Re: Tom Dugan]
      #1800591 - 08/25/07 11:20 PM

Wow! Hadn't thought of that. Rats!

What am I gonna do with all those universal joints?

Art


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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1823490 - 09/06/07 06:34 AM Attachment (81 downloads)

I woke up early so I spent some time on the CAD system to see if I might successfully harness the precision of that CAD environment to define a light box.

The intent of course is to replicate the one Ed Jones made.

I finally succeeded!

Previously I'd tried the folded paper routine that Ed demonstrated with a paper template of the conical geometry. It works but I could not get comfortable with the result to the point where I was willing to invest time and materials.

This time when sketching the model, I eliminated the tapered conical and simply modeled the light path. When I did, I mirrored the incoming angle on each mirror about a perpendicular line so that the outgoing image was at the same angle as the incoming ("angle of incidence equal to yadda yadda").

I told the system that no matter what, the incoming optical center line and the outgoing one, must be perpendicular to the hardware planes that the objective and EP were fixtured to.

With that done I simply tweaked and pulled angles by hand until the measured optical path was equal to the F/L of the objective.

All the dimensions you see, except one, are driven. They simply reflect the length of the part and do not determine it. The one that was fully defined was the objective lens plane.

The mirrors for this are two 1/10th wave, 50mm diameter optical flats from Surplus Shed and will be used with a 68 x 360 achromat.

I know that if I sat down and played with this, I could capture a macro that would allow me to simply type in values for the objective lens and have the system adjust the model.

The problem with that is that it takes a lot of time to write the algebraic formulas and debug the program and I've no time or interest in doing that.

Besides, I only expect to build one of these. If I were going into production (ugh!) there might be some justification.

Now, for the record, I measured to the inside surfaces.

In fact the lens will be mounted inside the box. This will displace the optical origin of the lens and thus move the exit outside the box. I want that so I have some latitude in focusing the EP.

I intend to mount each mirror with a piece of inner tube glued at one edge (or a dob of silicone) and two fine threaded plastic screws pushing from opposite corners to fine tune collimation. To do that I may offset the walls by the combined thickness of the mirrors and the rubber. No problem.

I anticipate cutting a length of cardboard and folding it as shown, fitting it to a plot of the pentagon laid on the bench. That should be sufficient to verify placement.

I've already laid up one half of the composite sandwich from which this little jewel will be built. I only need to do the other side, for which I have chosen black satin Formica.

Remember please, optics are not one of my strengths so if you see something suspicious or inappropriate, please chime in.

Thanks!

Attachment

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Jeff Morgan
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #1823823 - 09/06/07 11:08 AM

I feel so dated with my 15 year old copy of MacDraft ...

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Ed Jones
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1824037 - 09/06/07 01:07 PM

I got another objective from SS 50X220 mm. It had some separation of the balsam so I hit the flint element with the flame of a torch for about 15 seconds and it popped apart. I cleaned it up, recemented it and now I'm ready to do the paper thing again for another finder too.

--------------------
Ed Jones




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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #1824069 - 09/06/07 01:19 PM

Jeff this wasn't a 3D model, simply an intelligent 2D sketch.

I suspect it can be just as easily done in MacDraft.

The problem wasn't the software. The problem was in my approach.

Art


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Tom Dugan
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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1824204 - 09/06/07 02:16 PM

Quote:

I got another objective from SS 50X220 mm. It had some separation of the balsam so I hit the flint element with the flame of a torch for about 15 seconds and it popped apart.




Sure it was just a 50mm lens, but...
OY!

--------------------
Antares 10" Dob
Orion 150mm Mak
Orion 100mm EQ refractor
Homebuilt w/ Stellarvue 102D lens
Homebuilt w/ Antares 120 mm lens
Coulter 1st generation 13.1" mirror (waiting patiently)
Unknown number of binocs
Parts, parts, parts
More parts


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Re: Folded Refractor First Light new [Re: Tom Dugan]
      #1824630 - 09/06/07 06:15 PM

It's not as bad as it sounds. It works pretty well, I've separated a number of doublets this way. You want to heat the surface fast and evenly but not too long. Always heat the flint, if one of the lenses is FK glass it will certainly break doing this. I only paid $6 for this lens anyway.

--------------------
Ed Jones




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Re: Folded Refractor First Light new [Re: Ed Jones]
      #1825012 - 09/06/07 09:25 PM

Ed it's remarkable how alike the angles are in our two reflective refractors.

I've got a lot of household chores that MUST get done this weekend. Not sure I can get to this soon.

Art


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Re: Folded Refractor First Light new [Re: rboe]
      #2115308 - 01/12/08 01:29 PM Attachment (50 downloads)

Quote:

Jeff; I strongly suspect a small base for the forks to mount on. If you made the disc the same diameter as the width of the forks this would take advantage of the natural stiffness the forks provide.

In turn you will need to add some bracing from the larger base to the pier post to stiffen this wider base. Double thick BB for the base would be a good idea too.




It's been a slow few months in the Wile E. Coyote Amateur Telescope Workshop. However, I did get a chance to implement a few of the changes suggested.

1) I reduced the overall weight the mount has to carry. This was done by removing about 3-1/2" of wood (almost one pound) from the nose of the telescope. Since this is an inherently nose-heavy design, it allowed me remove about 3 pounds of counterweights from the back. Of course, the wood splintered during this operation. So I routered that away and installed mahogany strips to cover that little error. (While using 1/2" Baltic Birch and a plate joiner made construction fast fast fast, if I had it to do over, I would take a router to the front and mill some of that wood off.)

2) The leg sections were beefed up to 1-1/2" thickness. They are still detachable however.

3) Turnbuckles were installed from the end of the feet of to the top of the pier.

I had a chance to test mod #2 separately. Surprisingly #2 made little difference. However, the turnbuckles made a huge difference. The damping time is down to less than two seconds, and I can probably tighten them a bit more without pulling the anchors out of the wood.

The mount still does have some unwanted wiggles. I clamped the fork to the cast iron table of my table saw, and that tested out well. So, I think Ron is correct, the remaining source of the wiggles is the interface between the fork (about 16 inches wide) and the top of the pier (about 6 inches wide). Just too much room to rock.

I have enough wood in the shop to enlarge to base. Next weekend I should (may?) complete the 12-1/2 Dob, so the folded refractor can go back in for one more modification.

Attachment

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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Art Bianconi
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Re: Folded Refractor First Light new [Re: Jeff Morgan]
      #2115379 - 01/12/08 01:56 PM Attachment (50 downloads)

I can see where the wire shrouds an turnbuckles would tension up the mount in compression. However, they won't do much for torsional "wiggles" (that's a technical term I learned in school)

Frankly, I suspect that you can get a lot more mileage with a lot less weight by simply building a triangular platform to attach the fork tines to and from there down, install three triangulated legs made from crutches.

You simply can not beat a truss for 3 axis stiffness.

The secret to mechanical stiffness is less in the material and more in the geometry of the structure.

I've shown the Bino pantograph I built using wood crutches. Here is the same concept, also using crutches, only aluminum ones. It's even better than the wood ones.

It's a simple project to make. A 12 hour day if you work fast. A leisurely weekend project otherwise.

Here it's shown with a CG-4 head on it. In the background is the orginal tripod.

Art

Attachment

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #2115414 - 01/12/08 02:10 PM Attachment (48 downloads)

Here is the original binocular mount with a 13 pound lead weight suspended from the head. Amazing what that load does to the Mount's rigidity. The torsional stiffness is not as good as that provided by the stiffer aluminum crutches.

The twisting oscillations that scopes exhibit is exaggerated by their mass. The heavier the OTA, the more energy it stores when displaced. When the scope reaches the limit of the twisting cycle, it unwinds and releases all that energy in the other direction where the cycle is repeated. If, as you said earlier, it takes five plus seconds to stop, then that strongly suggests that the scope is not vibrating so much as twisting back and forth around the vertical axis.

Unless the support system can dampen or resist that movement, it continues back and forth until the natural dampening eventually brings it to a halt.

A truss based triangular mount will cure most of not all of that. Making the OTA as light s possible will also contribute.

Art

Attachment

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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dromedar
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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #2115501 - 01/12/08 02:49 PM

Tom and Art how did it go with your folded minitelescopes?

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Re: Folded Refractor First Light new [Re: dromedar]
      #2115798 - 01/12/08 05:13 PM

I made up one side of a composite sheet but got sidetracked by the 8" scope project (it's almost done).

I need to bond black laminate to the other side of the fiberglass with epoxy.

The raw material is almost ready.

Maybe next week.

Art

--------------------
“Everything is on its way to somewhere. . . . . everything!"

____________________ George Malley (John Travolta)
________________________ "Phenomenon"


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Re: Folded Refractor First Light new [Re: Art Bianconi]
      #2116321 - 01/12/08 09:46 PM

Quote:

Frankly, I suspect that you can get a lot more mileage with a lot less weight by simply building a triangular platform to attach the fork tines to and from there down, install three triangulated legs made from crutches.

You simply can not beat a truss for 3 axis stiffness.

The secret to mechanical stiffness is less in the material and more in the geometry of the structure.

I've shown the Bino pantograph I built using wood crutches. Here is the same concept, also using crutches, only aluminum ones. It's even better than the wood ones.

It's a simple project to make. A 12 hour day if you work fast. A leisurely weekend project otherwise.

Here it's shown with a CG-4 head on it. In the background is the orginal tripod.

Art




There is an additional consideration with this scope - the eyepiece location is in rather tight. It's the reason I did not do tripod legs in the first place. In my early drawings it looked like my legs and tripod legs would be in serious conflict.

Increasing the base size will be a simple project, especially since I have two scopes to use meanwhile. But I must say you have me tempted to pick up some cheap pine lumber and do a full sized mock up. Perhaps it will not be as "in the way" as it looked on paper.

--------------------
Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making


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