Re: ATM A large refractor experience

["Dwight K. Elvey" <dwightk.elvey@amd.com>]

>From: "David Lonard" <lonard@hotmail.com>
>
>
>Dear Group,
>
>I would like to relay my experience concerning the
>impulsive purchase of a large Kaiser Electro Optics
>surplus objective that I obtained from
>Surplus Shed for others that may get their hands on
>one of these.  It has 11" clear aperture
>and is stated to be a triplet oil spaced f/3.3 objective.
>The outward facing side is strongly convex while the
>side facing the eyepiece is less strongly concave.
>Ronchi star testing revealed very straight lines,
>so it appears to be well corrected for viewing
>objects at infinite distance.  The down side is
>that is displays considerable chromatic aberration
>on bright objects, jupiter had a nasty violet halo
>around it, although it does resolve detail down to
>about as well as southeast Texas skies will allow.
>
>As for its more realistic use as a wide field, ultra
>bright, deep space avenger, I noticed some field curvature
>with a 25mm plossl and I can barely reach a satisfying
>focus accross the whole field of view but it frames
>M44 really well.
>
>I have since built up a telescope around the massive
>objective.  See:
>
>http://www.geocities.com/lonard3/tele1.JPG
>http://www.geocities.com/lonard3/tele2.JPG
>http://www.geocities.com/lonard3/tele3.JPG
>http://www.geocities.com/lonard3/tele4.JPG
>
>Does anyone know more about these objectives, or
>perhaps indulge me with some sort of strategy
>to abate its chromatic aberration?

Hi
 Orion has just added some sharp cutoff filters
for refractor use.

>  I have already
>been told that one of the commercially available
>means to do this wont work for me.  Also, excluding
>exit pupil concerns, if I wanted to try my luck
>with a longer focus eyepiece, what eyepiece would
>be better at coping with the field curvature
>of a fast f/3.3?  A Nagler, panoptic, plossl...

 You need to have a field flattener lens. Unless the
eyepiece is specifically designed for a f3.3, it
won't focus well across the field of view. It might
be interesting to see how much the focal plane is
distorted. I doubt that selecting some arbitrary eyepiece
will solve your problem. This problem is aggravated
by the fast primary. There are some eyepeices that
are intended for fast primaries but I'm not sure
which they are.
Dwight


>
>David
>
>
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