A 60mm department store refractor started it all....
Active instruments: 4.25" f/6 Newtonian on altazimuth Springfield mount with crutch tripod -- telescope for the handicapped. 12" f/6 Newtonian Telescope maker since 1958; always more to come? Well maybe just one more and it will be something very special Stellafane Awards: 1977 1st award for 4" f/6 refractor 1978 1st award for 4" f/4 Lurie Aplanat 1983 1st award for Newtonian smoking pipe For Sky and Telescope articles, please see Bio info.
Quote: was hoping that a zemax jock would have taken up the challenge....
17.5" Dob "Beta Version"
NP 127 on a CG-5 and CGEM DX
25x100 and assorted other binos
Naglers, Ethos and various others.
Quote:A $150 Petzval, should be bigger objective but the corrector should be the same. Astrozap tried it for $1200 and apparently failed, the NA140SS is a 2k Scope, somebody should be able to do it in a Petzval F6 for $4k..... If you look at the 6" triplets out there at F8 for 8k.....
Quote:Jon, vixen describes the 140 as "The advanced 4-element objective lens, set in two groups, minimizes residual chromatic aberrations. With its unique Petzval like correcting lens at the rear, this Neo-Achromatic refractor telescope is specifically designed to provide improved color and a flat field, ideal for astrophotography.The AT65 Quadsounds like the scope you are looking for a little small but... fast and flat.
Quote:Jon,While OT, if you want to scan vast nebulosities, think bino with filters. Two eyes do a lot here...
Quote:A strict Petzval reduces colour aberrations not field curvature as was mentioned early on
Quote:I have seen a design for a Petzval type some where or the other that was flat field and an apo but only 100mm dia F8 and the "lens" was about 500mm long.
Quote:That's a 106mm and if you look at this you can see what I mean about the lens length. I wonder if they stole the idea from the one I saw on the web? A modified Pertzval as is this one.http://www.takahashi-europe.com/en/FSQ-106ED.optics.phpIt's wouldn't just scale up to 6ins. One of the problems is that the diffraction spot is determined by the F ratio. The focal length of the 106 is 850mm. A 6in would have to be 1200mm so the ray aiming has to be that much better because the spot size has to be the same. Another problem with lenses that have that much space between the elements is temperature - distance changes. I think this is one of the reasons why the design has never really been popular but can be good for smaller lenses.John-