Telescope Reviews: 4.5" F4.0 Aerial Camera Lens Telescope Completed

This was my project over the holidays. Bought an F4.0 Aerial Camera Lens from Surplus Shed just before x-mas for $175. Since I only own long focal length scopes, I felt a good Rich Field would fit nicely in my collection.

Specs appeared pretty good so I went for it. This is a 7 element lens assembly for 4.5 x 4.5 inch film and color corrected from 4900 to 7000 angstroms with 82% light transmission. 5 inch diameter front lens element. Total lens assembly weight is 15 lbs (heavy).

The design of the telescope evolved based on what I had laying around and what was at my local surplus store. One of my aluminum scuba tanks was made with a defective alloy and can no longer be filled. The scuba tank diameter was a perfect fit for the flange of the lens assembly. A 2-speed crayford focuser had to be purchased. I also had an old transmission jack not being used. Some 2" square aluminum supports left over from my fence and some other hardware from the local store completed the design. A local machine shop cut and milled the scuba tank for only $50 (good deal). Used a laser pointer for collimation. A little paint and "Sky Diver" was ready for the first clear night.

The Star test: I will try to summarize the 6+ good night of viewing I have had. I tested using eyepieces ranging from 52mm to 3mm with brands including Nagler, Seibert, Rini, Celestron, Smart Astronomy, and Meade. What amazed me the most was that all eyepieces keeped the flat field from edge-to-edge. I had expected only my Nagler 13mm Type 6 would be able to maintain flatness because of the Fast F4. Not the case. Stars were pinpoints across the complete field for all. Magnifications up to 150x still produced excellent views. (Jewels in the sky).

The Disappointment: This scope will not handle bright objects well. Mars, Sirus, and the Moon produced a significant purple halo around the object. I did expect this to some degree when doing my research. I installed a yellow filter which is commonly used on aerial cameras. The purple halo now turned yellow and was still present. I finally stopped the scope down to a 3" diameter hole using construction paper. The halo went away giving a pretty good view of each object.

Next Test: Will try different filters and try to split some double stars.

Overall, I built this as a rich field scope with no intention of high mag viewing. As a rich field, this is a high quality scope with excellent optics. Bright objects will be viewed with my longer focal length scopes.

Any comments would be appreciated.

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Dick
6" f22 classic catadioptic (homemade)
5" Nexstar5
4.5" F4 Refractor - Sky Diver
4.5" celestron reflector
3" Goto Refractor