Re: ATM "Short" Focal Length 2" Eyepieces?

["David File" <davefile@usa.net>]

Karl,
   I thought you'd get a better technical answer than those given so
far...so here's my try.
   Similar, basic reasons to why you don't see f2 telescopes also govern the
objective lens.  Lower f ratio optics don't always have a "flat" focal/image
plane.  As the focal length is reduced so the diameter must reduce as well.
A 40mm 2" eyepiece would have an aperture of ~40mm yielding an f ratio for
the objective of 40mm/40mm= 1.  If you have a .925 or 1.25 short focal
length eyepiece check their f ratios...check them all.  There may be some
ways around it technically but this a simple guess.
  Any way...if God had meant us to use short focal length objectives he
would have given us a steadier sky.

Regards,
Dave

----- Original Message -----
From: "Karl E Lewis" <kal1971@juno.com>
To: <atm@shore.net>
Sent: Friday, March 16, 2001 11:56 AM
Subject: ATM "Short" Focal Length 2" Eyepieces?


>
> Why is it that we don't see eyepieces shorter than 17 mm in a 2" barrel?
>
> TIA,
>
> Karl
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