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1 1/2" eyepices--vs.--2" eyepieces @ 32mm?

Started by tomdisco, 03/11/2003 04:43PM
Posted 03/11/2003 04:43PM Opening Post
At what focal length is it no longer practical to stay with 1 1/2" eyepieces in favor of 2" eyepieces? I have read that at some point you are just looking at the insides of the eyepiece barrel unless you move up to 2". Also, what is the influence of advertised FOV in respect to this decision?

I have a Meade Series 500 40mm plossl which came with the used scope I purchased (f/10 C9.25). The difficulty seeing anything with this eyepiece unless I am dead center with my head in a vise makes this piece just about worthless to me. The next nearest focal length I have is the Celestron silver top 25mm plossl. Without trying someone else's eyepieces in my scope I'm fearful that something like a Meade 32mm SP or Celestron 30mm Ultima may prove a dissapointment when I should really be considering something like the 2" Meade 32mm SW or other similar eyepieces.

Can one really get good 32mm performance with 1 1/2" eyepieces or is this pushing the limit?
Posted 03/11/2003 07:32PM #1
i love my u.o.32 konig 1.25 format, fairly wide field of view great eye relief barlows very well, all around good performer at a very resonable price. john
Posted 03/11/2003 09:20PM #2
The eye relief on a 1.25" 40mm Plossl is too long. That's what causes the problem. This is not really a 1.25" versus 2" problem, but I think with long focal lengths and long eye relief, smaller apparent fields of view are that much harder to use. I.e., for ease of use, it is better to have 32mm focal length and a 50 degree apparent field than a 40mm focal length and a smaller apparent field. I do think that in the 1.25" size, 32mm is as long a focal length as I would want. Many people seem to like the 30mm Ultima better than 32mm Plossls.
--
Mike
Posted 03/12/2003 04:03PM #3
Depends on the eyepiece design. In typical 50-55 degree FOV (i.e. Plossls, Ultima), 30-32mm is about all you can go before the format becomes a limiting factor (i.e. the barrel restricts the FOV). For wide field designs (70+ degree FOV), the limit is about 20-25mm.

As the other Mike said though, your problem is not restricted FOV, it's too much eye relief. A long rubber eyecup might help position your head, but a 30-32mm should prove to be much better.