Re: [ATM] More on aperture stops

[Mark Holm <mdholm@telerama.com>]

Jay Kirkland wrote:
 And is there any reason that using an
> off axis mask (smaller image size when the light reaches the eye?) that 
> would cause a 3" scope to alleviate astigmatism or other eye effects 
> seen in a 10" scope while using the same eyepiece?

Yes, already noted in my first reply to this thread.  Reducing entrance
aperture at the same magnification reduces exit pupil proportionately.
Reducing exit pupil directly reduces entrance pupil to the eye  1:1
relationship there.  Most human eye lenses are better in their central
portion than in their outer zones.  Thus, reducing entrance pupil can
have a very significant effect on image quality at the retina.

One thing I am wondering is, did the original poster on this thread have
RK or LASIK eye lens surgery?

On another subtopic of this thread, I think a ghost image type of
reflection in an eyepiece ought to move in a direction opposite to the
main image when the subject is moved off center.  Does this sound right?

As for seeing the same effect in a lot of scopes on the same night, this
rather stongly points to an atmospheric phenomenon, a peculiarity in the
observer's eye, or perhaps in an eyepiece, if the same eyepiece was
transplanted into all of the scopes.

Mark Holm
mdholm@telerama.com

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