Re: [ATM] Offner layout question

["Scott Milligan" <starzkey@charter.net>]

Ric:

Aside from the inevitable astigmatism that this configuration would
introduce (shouldn't be too much of a problem so long as the vertical offset
is near zero, assuming a horizontal cut-off), I think the answer to your
question depends on whether the Offner null in question was designed to work
as a single-pass (i.e. similar to Dall test) configuration or not.  

Most Offner nulls are designed assuming a double-pass, auto-imaging mode,
and therefore using one of these in single pass would only correct 50% of
the spherical aberration one is trying to null.



Scott Milligan
 
 

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Ric Rokosz
Sent: Wednesday, October 25, 2006 11:43 AM
To: atm@atmlist.net
Subject: [ATM] Offner layout question

I was loking at a Offner layout used to test both a 24 and 30 inch scope:

  http://www.hkastroforum.net

look for a atm message and work backwards (most replies are in English -
they got their lenses from Ortho eyepices)

Anyways,the knife edge for the tester was to the side of the Offner
assembly.I had always assumed you need to view the return beam throught the
lenses as in the Ross.Wonder if this is O.K. ? Would imagine the offset
would introduce some (lot?) of error.

Ric


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