Re: [APML] Fun in southern France

[Philip Perkins <philip@astrocruise.com>]

Hello Bobby,

Yes, Chuck's OAG is a 2.7", however it narrows down to just 2" at the 
camera end because it takes the standard Lumicon 2" OAG adapter.  That's 
where the problem is - i.e it was only designed with 35mm in mind.  You're 
right - nothing that uses 2.7" focuser parts will fully and evenly 
illuminate the full 6x7 frame, however removal of the 2" obstruction will 
make a big difference.  Also it needs a decent Pentax adapter that is 
solidly fitted to the OAG.  I reckon that using the 2.7" focuser with 
correct adapters for the camera it should be possible to evenly illuminate 
the short dimension of the 6x7 frame which, if memory serves me is actually 
56mm on the negative?  To get the entire frame evenly illuminated would 
require a 4" focuser and OAG.  I could probably get close to that field 
with my RC since it is specially adapted for such use with a larger than 
normal secondary.  But before that I'd like to remove the obvious 
obstruction and see if I can get 56mm evenly illuminated.  I think that 
would make me happy.

The Hutech OAG looks very interesting actually and I will check it 
out.  Thanks for the link!  They say they provide a Pentax adapter for 
it.  It might be a better bet than trying to adapt the existing OAG.

But as you pointed out, before considering further serious investment in 
medium format, it's important to know that at least one good 120 colour 
film will be available for some time into the future.  I would go the Tech 
Pan route but unfortunately f/9 is not really viable for tri-colour film work.

Thanks
--Philip


At 13:53 29/12/01 -0600, you wrote:
>Is Chuck's OAG a 2.7"? I have the Lumicon 2.7" OAG but I doubt if it would
>allow illumination of the full 67 frame even with a proper larger adaptor
>than you use. Here's an OAG possibility:
>http://www.sciencecenter.net/hutech/mitsub/oag.htm
>I'm not sure but I think they have a Pentax 67 adaptor for this OAG. One
>would still have to find a place for the FF.
>A fellow could probably have a proper OAG machined if he would use the
>Lumicon pick-off prism assembly for the guideport. And a re-fitted GEG would
>work with enough backfocus, but newts won't have that much.
>The 67 frame will probably still be vignetted with a 2.7" focuser even with
>oversized OAG and adaptors, but one would get more than 35mm coverage. You
>get 45mm now. How much do you think you could get with your focuser and
>larger adaptors and OAG?
>Bobby



Philip Perkins - philip@astrocruise.com
Wiltshire UK & Luberon France
Astrocruise - http://www.astrocruise.com


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