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Posts Made By: Tom Rodstrom

May 4, 2002 08:58 AM Forum: Off Topic Discussions

How do I send e-mail?

Posted By Tom Rodstrom

Is there a way to send an e-mail directly to someone who posts on a forum?

May 27, 2002 03:33 PM Forum: Telescope Making

Wounded 5" Petzval - Part 1

Posted By Tom Rodstrom

A few years ago I bought a 5" Petzval OTA from a surplus store. It is an interesting design with Clark objective and a two element 5" coma corrector. The last surface of the corrector is 5" in diameter with a 1.2" sagitta. It had a 3.5" x 4.5" ground glass viewing plate at the focal plane. I cut 6" off the end of the tube, added a focuser, installed a dozen baffles and had a nice refractor. The focuser tube extends up to an inch into the sagitta of the last lens.

I noticed that there was a lot of ghost reflections when looking at Jupiter. Looking through the scope I noticed that the coating on one of the lenses was mottled and I thought that was the cause (wrong). I posted a question on Astromart (I think) and was told that Kodak lens cleaner might remove the coating. I tried it and it worked, but I had to rub hard using old cotton underwear.

When I put it together, it didn’t perform nearly as well as it had. Part of the problem was collimation. I did some star tests and was able to get much better results by rotating lenses in their cells. The outer lens of the objective has four large pock marks and there is astigmatism in that area. The star test also has spikes and I thought that I had put scratches in the lens where I removed the coating. The ghosts turned out to be more from the eyepieces I was using than anything else.

June 10, 2002 08:16 PM Forum: Telescope Making

Jaegers 4" F15 Cell Assembly

Posted By Tom Rodstrom

I just received a Jaegers 4 1/8" F15 OTA. At my request the seller removed the objective cell from the tube and shipped it separately. He also removed the lenses from the cell. I need to assemble the cell. The two lenses both have a pair of 4's on the side and a "V" shaped arrow and lines. The DCX lens has one line on it and the meniscus lens has two. The cell has a line scratched onto it in the inside. There is also a 1/8" spacer that looks like it goes between the lenses.

Does anyone know how to correctly assemble this objective cell?

June 16, 2002 09:59 PM Forum: Eyepieces

Poor man's Radian

Posted By Tom Rodstrom

I have a new favorite telescope (Jagers 4" f15) and a new high power eyepiece. The eyepiece is 4mm with a 50 degree field and generous eye relief. I don't know how to measure eye relief, but it is comfortable, better then a Celestron 10m SMA. It weighs 1 ounce so balance is not a problem. It star test's very well and I've been using it this evening at 393x to study the moon. The test was a small rille just north of Maskelyne (a crater on the southern edge of the Sea of Tranquility). This eyepiece is sharp from edge to edge and shows the rille well. It is better than an 8mm Konig II with an Ultima barlow.

The eyepiece is actually a plastic Computar 4mm f1.2 CS mount CCTV lens. The barrel o.d. is 1.266" so I'll have to turn it down a little in a lathe, but it's a keeper. The scope is too - it knocks my socks off!

June 28, 2002 06:42 PM Forum: Refractors

Jaegers 4" F15 - Breathtaking performance

Posted By Tom Rodstrom

I recently picked up an old Jaegers 4" F15 OTA and I am absolutely amazed with the performance. I haven't been outside the city (San Diego), but the moon at 392x is incredible. I was able to see the three craters in Plato. Two were dots and the central crater started had a little shape. The views were still very sharp at 95x per inch. The biggest problem I had was the floaters in these old eyes.

I had trouble believing the performance so I just did a test comparason with a 5" F7.5 Petzval refractor which has been my main scope. This time target was the trusty power line insulator (1/2 mile away) that I use for tests. At 237x the 5" was starting to loose contrast. At 255x The Jaeger was like being there. At 492x the image was still better than the 5" at 237x. There was a little violet halo in shadows (black) where they where next to the bright sky in the background. Resolution seemed to be limited more by seeing than resloution.

If I get my van running tomorrow I'll head for some dark(er) skies. If I knew the performance, I would have had a slow refracter long ago. I have studied that insulator with every scope and eyepiece I have ever owned. I still cannot believe my eyes. Is this performance common or do I have a brain problem?

July 21, 2002 11:06 AM Forum: Telescope Making

8" F5 40"fl Perkin Elmer Lens - Need info

Posted By Tom Rodstrom

I just bought an 8" F5 fixed focus camera lens. The objective is marked "DISTORTIONLESS TELEPHOTO AERO LENS 40" (1016MM) F/5.0 T5-Y7-068 MADE IN U.S.A. BY PERKIN-ELMER CORPORATION, NORWALK, CONNECTICUT" and there is another label marked "FIXED FOCUS LENS" and "Gorton Industries".

It appears to be a four element design with an 8" two element air spaced objective and a 5" two element corrector about 2 ft down the tube from the objective. Is anyone familiar with this lens?

There is no fucuser, but I did hand hold a couple eyepieces in the 25mm to 55mm range and with the proper orientation was able to get some views without much color. I assume that collimation is critical on an F5 lens. I have a way to install a focuser without hurting the tube. How do I check collimation when I install it?

July 21, 2002 12:36 PM Forum: Telescope Making

Optical Design Software

Posted By Tom Rodstrom

I have a 5" four element refractor with a bad objective (asitgmatism). I have measured the curvature and density of the glass for each element. I would like to find a good shareware/freeware program that would let me back out the design. I could then (I hope) see if I could find a commercially available 5" objective that could be spaced correctly for this scope. Any help or suggestions would be appreciated.

July 21, 2002 05:47 PM Forum: Telescope Making

How to cut a 4" wide x 1/2" thick mirror diagonal

Posted By Tom Rodstrom

I have a 4" x 8 1/2" x 1/2" first surface mirror that I want to use to make a diagonal. It will be used with a home made 55 mm eyepiece that has 62mm field stop and a 2.3" eye lens. The scope is a four element 5" refractor with a 5" diameter sweet spot so I hope to get some very nice wide field views.

In order to use the mirror as a diagonal, it needs to be cut down to about 5.7" in length. If there is a shop that does that sort of thing, I may send it out. Otherwise, I must do it myself. My best idea is to use a motor driven string on a couple pulleys. It would run through a slurry of grinding compound (grit?) and over the mirror. What's your suggestion?

September 14, 2002 06:52 AM Forum: Telescope Making

8" f5 Refractor Lens Respacing

Posted By Tom Rodstrom

I have a 8" f5 four element refractor. I believe it is a Petzval design. It was used in an areo spy camera in the 70's. I have done a quick test and it has quite a bit of color. It came with a minus blue filter so I believe that it is optimized for a wavelength outside the visual range that cuts through haze.

I hope that it can be respaced to move the correction into the visual range. It will probably be quite an undertaking, but I think it would be worth it. Does anyone know how to accomplish this task, or where I might get useful information?

I also have a 6" triplett with the same problem.

September 14, 2002 10:01 AM Forum: Equipment Talk

8" f5 Refractor Lens Respacing

Posted By Tom Rodstrom

I have a 8" f5 four element refractor. I believe it is a Petzval design. It was used in an aero spy camera in the 70's. I have done a quick test and it has quite a bit of color. It came with a minus blue filter so I believe that it is optimized for a wavelength that cuts through haze outside the visual range.

I hope that it can be respaced to move the correction into the visual range. It will probably be quite an undertaking, but I think it would be worth it. Does anyone know how to accomplish this task, or where I might get useful information?

I also have a 6" triplet with the same problem.