Re: ATM Eight inch F8 Design

["Anderson, Jay" <andeja@mail.va.gov>]

At 09:40 AM 6/18/97 -0400, you wrote:
>should design for the smallest possible secondary that still gives the
>eyepiece full illumination.

Brad Davy writes:
>This is the term I'm having problems with.  How is "full illumination"
>defined?  Should the "full illumination" area be equal to the diameter of
>the eye piece?

IMHO, the secondary should be just large enough to accommodate all of
the light cone coming off the primary mirror (this minimizes
obstruction).  Then all of the light cone coming off the secondary
should pass into the eyepiece (light striking nothing but lenses--"Nutin
but net!") and then ultimately all of that light coming from the exit
pupil of the eyepiece should fit into the pupil of your eye without any
striking your iris.  In short, if you are designing a scope that is
optimized in this fashion then it will efficiently make use of every
possible photon passing through the scope's aperture and concentrates it
all on the retina of your eye.   The pupil of your eye ranges from 3mm
to 9mm and though older folks usually have the smaller eye pupils there
is a wide variance and you could be 90 years old and have a 9mm pupil.
There are ways to measure this accurately so you can build the scope
around your eye.  If you had a 9mm eye pupil and then designed the scope
for a 8mm exit pupil (allowing 1mm for 'slop') you would have a
wonderful image but others with smaller pupils would have trouble seeing
the whole image field at once--keep that in mind.  If the exit pupil of
the eyepiece is very small... say 1 mm or less then you may see the
blood vessels of your retina and other distractions like "floaters" and
other flaws in your own biological optics overlaid onto the image.  Not
sure?   Design for a 5mm exit pupil--that covers just about everyone.
This may be taking things a bit far... to the extreme... but sound like
there are a lot of 'extremists' out there like me. <smile>