Quote:
Originally Posted by Jason D
Above is a quote from the first reply to the OP which happened to be yours. You asked the OP to offset the secondary mirror away from the focuser to avoid vignetting which later you explained to be light cone vignetting. You did not question the OP to find out if such an offset is needed. I can tell
from the OP's photo that the secondary mirror is mounted centrally on its stalk without an offset. Asking the OP to move the secondary mirror away from the focuser unnecessarily will cause opposite spider vanes to be at an angle with respect to each other which will worsen the diffraction spikes. In addition, suggesting that the away-from-focuser secondary mirror offset is needed to avoid light cone vignetting is incorrect.
Jaosn
|
I am not sure why you insist I am in wrong here.
Yes, of course this statement was mine, the post is here to stay for all to see for all times, and I do not see any problem with it.
All I did in this thread was I gave an (free!) advice in attempt to help clarifying the cause of the problem (based on my own experience with Newtonian scope design), in an evolving discussion which at the end produced some results (and I never intended to claim at any time that my contribution is crucial for resolution).
Quote:
Originally Posted by Jason D
.... In addition, suggesting that the away-from-focuser secondary mirror offset is needed to avoid light cone vignetting is incorrect.
Jaosn
|
I disagree with this - offset may be needed to avoid the vignetting in case the scope tube is too narrow, situation clearly illustrated with your third drawing, and this is what I wanted to avoid in my design. Plus I wanted the optical axis of my scope to be paralel with mechanical axis of my tube (frame), also illustrated with your own drawing.
This offset is of course meaninless with open designs (and oversized tubes, used in Dobsonians).