On 9 Mar 2004 08:07:39 -0800, (Shneor Sherman)
wrote:

(Tom Roginski) wrote in message . com...
Pete Rasmussen wrote in message . ..


Interestingly the visibly used field stop location for the GSO 42mm is
effectively the very bottom edge (entrance ID) of the eyepiece barrel
itself. For reference, that's where the filter threads are located.

Pete

It's a bit difficult to see how the filter-thread end of the barrel
could be the field stop, as the cone of light is expanding as it
passes by the filter threads and maxes out where the the field lens
meets the focal plane of the inverted cone of light (where the clear
diameter of the field lens equals the diameter of the light cone).
That is the location of the field stop. Unless the field lens is at
the very end of the barrel, right at the filter threads, the field
stop cannot be at the filter threads.
Clear skies,
Shneor Sherman


I see it you aren't speaking to me directly, Shneor, yet I will reply
to the impersonalization.

I don't have a ray trace to understand why but the *effective* field
stop, as I wrote, is "visably used" at bottom of barrel for the
design. The actual focal plane is slightly higher up but the light
cone, for whatever reason, is factually clipped at the entrance where
the filter threads are located. This of course gives a "fuzzy" field
stop impression in normal use. I then explained that once a user adds
a further restrictive stop (ie. smaller eyepiece holder seat aperture
in the case of star diagonals) at the same relative point in space,
the AFOV of the eyepiece is reduced even more. This is without
question the case with this new eyepiece. Buy one and see for
yourself. I certainly don't lie about anything I write in review.

You indicate thrice about the field lens in eyepiece design, "meeting
the focal plane" and, "That is the location of the field stop" and,
"Unless the field lens is at the very end of the barrel, right at the
filter threads, the field stop cannot be at the filter thread". Well,
the field lens should never be *at* the field stop location as all the
dust attracted to the outer lens surface will be magnified and in
focus. Virtually all common designs have the field stop spaced
*before* the R1 surface or, in between elements like in the Nagler to
prevent this.

So, not to change the subject, did you not receive my last private
email response to your inquiry the other day? I kindly provided you
workable solutions to your quest to have wider true field with 1.25"
binoviewer eyepieces. One was concept to add an eye element to a 35mm
Ultima to reduce FL and increase AFOV so it would be useable in your
f/4 scope. I never did hear back from you and hope you are one to be
in appreciation of my time.

Pete