Compact Portable Dobsonian Telescope
The Optics acquired for the building the crate A scope prototype
While I was working on a 10″ f/5 Primary Mirror for the Prototype this past winter, my work area got too cold
and the pitch lap became too hard and brittle. This environment made polishing and figuring the mirror impossible.
I didn’t want to stop building this prototype so when I saw a used Meade DS-10 on ebay, I went ahead and did some research.
In the “SKY & TELESCOPE” ad from the 1980s, Meade claimed the following….
10 inch F/4.5 Reflecting Telescope. With null-figured, diffraction-limited Pyrex parabolic primary mirror
and matching 2.60” – 1/10 wave flat secondary”
I bought the DS-10 above and used the optics to design the crate A scope.
I assumed when I bought this DS-10 that the optical components were original to the scope, but the mirrors were not marked with any manufacturer’s name. Both the primary and secondary mirrors had aluminized coatings that were in very good condition. I didn’t have the equipment necessary to test the flat secondary mirror, but I did test the primary mirror. The Ronchi test revealed a good edge with a fairly smooth, parabolic surface. The foucault test also revealed a good edge and a smooth surface. However, after using my Faucault tester to take precise readings along with Figure XP software to calculate the results, I was able to determine a P-V wavefront error of between 1/2 & 1/3 wave for this mirror. Results? “Not so good”
I’m still not sure if this was the original primary that Meade supplied with this DS-10, but these measurements were not up to Meade’s advertised specs. Most likely, the original primary mirror had been switched out. I went ahead and built the first prototype around this mirror anyways.