Re: Eyepiece 'sizes'


"Rexx Magnus" <trashcan@xxxxxxx> wrote in message
news:Xns98F17476C95F5rexxdeansaund@xxxxxxxxxxxxxx
With my Meade scope, I have a 26mm eyepiece. The size of the lens in
it is quite big, which makes it easy to point a camera down it and
take a photo (just for quick shots).

I've recently bought a cheap Celestron eyepiece (9mm) and the lens is
much smaller in diameter, and nearer the top - so your eye is almost
touching it. Because of how small the area you can see through is,
it's almost impossible to use a compact camera with that eyepiece. Is
this just due to the fact that it's a 9mm, and are most 9mm eyepieces
likely to be the same configuration? (This is a plossl, whereas the
26mm is a 'super plossl').

If I bought the Meade eyepiece of the same spec, would it be likely to
have a configuration closer to that of the Meade 25mm eyepiece ie.
larger lens and further away from your eye?
The simplest solution, is to do what is done 'at heart' on more expensive
eyepiece designs, and add a Barlow. If you look at the internal designs of
more 'premium' eyepieces, generally, the shorter focal length units, will
include an element that is effectively functioning as a Barlow lens, to
get away from this exact problem. For a given AFOV, and a given lens
design, the diameter of the exit element will reduce as the focal length
goes down, and normally the eye-relief will reduce as well. The 'super
Plossl', might be fractionally better in this regard (but not a lot).
Unfortunately, the term covers a whole range of eyepieces with a
significant 'range' of designs, normally small modifications to the basic
'Plossl' design, so one needs to go for something beyond this to get a
real solution.

Best Wishes


.

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