Re: [ATM] sizing secondary mirrors,and the size of the 100% illuminated field

["Bob May" <bobmay@nethere.com>]

Prepare the guns for ACTION ! ! !
Please note that a lot of this is all relative to the
application.  One person may be satisfied with a FOV of 10mm
while another will want a 45mm FOV on his scope for a fully
illuminated field.  Don't bother to argue with either fo them
because that is what they will find acceptable for their
purposes.
Another thing that I will note is that a 70^ illumintated zone is
about 1/4 mag. drop in intensity from the 100% illumination and
that isn't much in reality.  You can see it on a photograph that
shows the background illumination buy you probably won't notice
it with a visual inspection of the view.
I'll note that the R&VR value is more for 1.25" EPs as this is
about the size of higher power EP FOVs.  Lower powers will be
seeing the vignetting to about that 1/4 to 1/2 of a mag and this
isn't objectionable for visual use.  For photograpy, larger
secondaries are usually recommended to get the unvignetted FOV
out to a larger size (providing that is the vignetting source!)
to get the image flatter in brightness.  Please also note that a
35mm film won't fit in a 2" focuser and you have to use something
larger to get the corners of the film exposed without vignetting
by hte focuser itself.
Now, what do you want to do with your scope???
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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