I made much better progress with figuring my big mirror once I stopped trying to use the ronchi test for figuring analysis and built a stepper motor-moved foucault test rig from an old scanner bed and a long-throw (50mm) 0.01mm dial gauge. then I was able to get repeatable test numbers to plug in to the figurexp software which is fantastic.
Quote:
Originally Posted by mura_gadi
Hello,
I have been looking at what is needed for both Ronchi and Foucault tester. The Ronchi eyepiece is the cheapest option and use with a star test. I need the dial indicator (Foucault) or a decent Ronchi screen, both are seen as expensive within my budget. (i have no budget atm tbh, so, its galvanized pipes and elbow bends if I wanted to setup a EQ pier out the back sort of attitude.)
The comment about the diffraction spikes comes from J Texereau again and tied in well with the plans for the F9 8" using a small secondary.
"At any rate the effect in the Newtonian reflector almost disappears if we make the focal ratio 8 or 10 and the diagonal mirror only large enough to accommodate the incident light cone"
Mind you he goes on to quote a secondary of about 1/8th of the primary, so, I need to get my head around the science of that statement. The effects of the obstruction on altering the diffraction figure are still a little beyond me atm. But I like reading...
Thanks again, your comments have been appreciated,
Steve
Newt for the web has my secondary at 31mm with a ID of 9.01inches, J Texereau seems to suggest closer to 25mm for the secondary at this focal length.
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