Quote:
Originally Posted by Satchmo
Stephen
Thanks for the report . You really need to test your mirror on stars as that will tell you something about your mirror. A quality 100 lpi grating at focus will give you even more detail about overall correction and zones. It is hard to tell anything much by looking at the Moon in between sharp and blurry at 5 X magnification per inch of aperture.
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Hi guys,
Been away awhile. Back to the task.Put the current 22" mirror to the 133 lpi grating at the eyepiece. Clear sky, but atmosphere somewhat unsteady (even Mars and Saturn displaying some twinkle).
Sighted scope up on Sirius (Altitude around 70deg). First tested at full aperture: figure appears well corrected across the greater part of the radius,( very smooth, straight lines (used 6 lines)), but most definitely the evidence of rolled down edge.
How large is the rolled edge? I have a number of aperture masks. 20.5", 19", 17.5". So tried the 20.5" and 19" masks. With the 20.5" still evidence of RE. Tried the 19" and still a trifle RE. When the 17.5" mask was in place no further sign of edge condition. At this aperture the Ronchi bars appeared dead straight, from edge to edge, of uniform thickness (parallel), were very smooth, this would suggest (to me) that the central 17.5" is in the "envelope". From the observation this central portion is free of humps,hollows, and zones. No observable astigmatism.
Would welcome suggestions as to how best to deal with the rolled edge, which from the above is evident on the outer 1.5"+ of the radius.
Currently well into the early figuring of the second 22"er. Also with high/ low zones near the edge.
Stephen.
