How do you define eye relief these days?

I have two new Naglers, 7mm and 9mm. Is there anyone out there with
these two eyepieces who can see the entire field of view, right out to
the edges, all the way around, without plastering their eyeball right
against the eye lens? Do these eyepieces really have 0mm of eye relief?
Do the manufacturers of 80-degree eyepieces have a new definition of eye
relief? Thanks!
Larry Brown
http://home.fuse.net/astronomy

Larry Brown wrote:
I have two new Naglers, 7mm and 9mm. Is there anyone out there with
these two eyepieces who can see the entire field of view, right out to
the edges, all the way around, without plastering their eyeball right
against the eye lens? Do these eyepieces really have 0mm of eye relief?
Do the manufacturers of 80-degree eyepieces have a new definition of eye
relief? Thanks!
Larry Brown
http://home.fuse.net/astronomy

I have the Nagle 7 and 9mm, and I also can't see the entire field of
view, particularly through the 7mm, unless I'm almost touching the
lense. However, to me, the slight movement of the head needed to get the
entire view is not a big deal.

Jim

jimcate wrote:



Larry Brown wrote:

I have two new Naglers, 7mm and 9mm. Is there anyone out there with
these two eyepieces who can see the entire field of view, right out to
the edges, all the way around, without plastering their eyeball right
against the eye lens? Do these eyepieces really have 0mm of eye relief?
Do the manufacturers of 80-degree eyepieces have a new definition of eye
relief? Thanks!
Larry Brown
http://home.fuse.net/astronomy

I have the Nagle 7 and 9mm, and I also can't see the entire field of
view, particularly through the 7mm, unless I'm almost touching the
lense. However, to me, the slight movement of the head needed to get the
entire view is not a big deal.

Moving the head enhances the feeling of looking through a "porthole." I
like it - but then it's all new to me, and I like everything; Maybe
it'll get old after awhile.

Larry Brown wrote in message ...

Do the manufacturers of 80-degree eyepieces have a new definition of eye
relief? Thanks!

Eye relief is a technical term which assumes an idealized
model of the eye. It is a well-known fact that the human
eye does *not* behave like this idealized model, so that
in practice your eye *always* needs to be closer than
the stated eye relief in order to see the whole field.
I get the following explanation straight from Al Nagler.

The reason is that as you slew your eye towards the
corner of the field, the pupil moves laterally, away
from the center of the eyepiece. If you slew 40
degrees to look directly at the field stop of a Nagler,
your pupil moves several millimeters, and when the
eye relief is small, that amount of motion may cause
the image to black out entirely.

Personally, I have considerable trouble seeing the
field stop in *any* Televue eyepiece, and have never
even come close with a Nagler. Granted, I have never
looked through a 32mm Nagler, which is where the field
stop is most likely to be visible. Therefore, I find
the useful FOV of most Naglers to be *smaller* than
in my Pentax XL eyepieces, with their 65-degree AFOV
and 20mm eye relief. Moreover, I find the inability
to see the field stop extremely vexatious in its own
right, since I routinely use it as a reference point
when estimating sizes, and also to place bright stars
out of the field when viewing faint objects.

- Tony Flanders

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