Re: [APML]: Pentax 67 Questions

[Robert Rose <RJR@usip.com>]

I have been using a Pentax 6x7 on a Meade 10" SCT for some time and would like to offer 
some different answers to these questions:

1.  Adaptors.  The only one I know about is the one Lumicon makes to mate the P67 to its 
Giant Guider.  It is composed of a Pentax brand reverse mount and a filter reducer.  With 
this adapter you could end up with any screw diameter you wanted.

2.  Use on an SCT.  Previous post writes "If you are thinking of using this 6x7 on a SCT 
forget it, you're wasting $$$. The SCT's just barely cover the diagonal dimension of the 
35mm frame."

With due respect, that is simply not true for the larger SCTs.

I have the 10" Meade.  The back cover plate is actually a thread reducer from around 3" 
to the standard Meade/Celestron SCT thread.  I take that off, and screw on a Lumicon 
Giant Easy Guider.  Then I attach the Pentax 67 to the Easy Guider.  This give me almost 
a 90% coverage on the 6x7 negative, with only very slight vignetting at the very corners. 
 By the way, the Giant Easy Guider gives 100% no vignetting coverage on 35mm, in 
particluar I know this is true on my OM-1.

The same guider will work for the Celestron 11" and 14" and while I haven't tried it, I 
suspect that you will get almost complete coverage on those scopes too.

So, all you need to do is plunk down enough $ to buy this stuff.  That being said, you 
wouldn't use the 67 for eyepiece projection photos.

It is also heavier and harder to balance the scope compared to a 35mm.  You also have to 
be sure the adapter is tight, so it doesn't rotate during exposure.  The ground glass is 
hard to focus on dim objects, but using a loupe (I use an 8x) is like looking at a field 
camera!

A real serious problem with the camera is shake from the focal plane shutter for speeds 
around 1/15 sec.  You might get that problem with lunar shots for example.  The camera is 
like a tank, and even with the mirror locked up (a must) that focal shutter comes across 
like gangbusters.

Bob
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
                                                                                          
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