-DannyMy warehouseMy Channel
Astronomy educator/Sidewalk astronomer
Owner of Astronomy Delight franchise
18 inch f4.42 Dob on eq platform w ST120 f/5 finder
12 inch Zhumell Dob
8 inch f/6.9 home made Dob with Seevers optics
William Optics red 10th Anniversary 80mm FD
C8 XLT on Vixen GPDX
26lb eyepiece box
Cernan Space Center astronomer
Member of Northwest Suburban Astronomers
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: Put it on a foucault tester, and ascertain the -exact- width of the TDE, if any. Use the principle of seeing the diffraction line all the way around the edge of the mirror, with equal, or darn near equal brightness both sides.M.
Quote:if you cut the hole the smallest you can progessively get larger to test the mirror and then fine tune the size [if there is a tde] with a new piece.so if you start at 2" smaller, 1" all around, you can make it larger in half inch increments.coroplast may be a little hard to cut in 1/4in increments. use fresh blades.
Quote:check out the spot test. look at the third image, it has a bright ring around the mirror, thats the diffraction ring, meaning no tde.
20" homebuilt truss dob 6" watson refractor
Quote: There is no excuse for having an 8" F/5 mirror look that bad of a sphere!!
Quote: Replace the slitless KE w/t plastic w/t a vertical scratch (virtual wire). place the tester inside of ROC. Align the testers lateral axis perpendicular to the OA (optical axis). Mark the mirror w/t sharpy (or use an Evert stick) at the zones. Move the tester laterally so as to align the shadow of the virtual wire over the marked zone and record the lateral measurement.LWT is a moving source test (virtual wire is above the source i.e., reflected & source ray are coincident).
Quote:The best way (and most sensitive) to test a spherical surface is with a null at ROC- no grating, spots, wires.
20 inch f8 Chief Ed Jones designed and a 17 f9 Zanbuto Wide Band Chief Mike Jones designed .Both unobstructed telescopes .