In a message dated 5/13/04 9:09:04 PM, starfest@comcast.net writes:
I am achieving three different focusing points with my Mamiya M645 using the
following three methods:
1) Tak FM60 with included ground glass against the film plane.
2) Tak FM60 placed on top of the focus screen after removing the prism.
3) Prism attached and Mamiya 2x magnifier attached to the prism viewfinder.
Each method brings me different results. I focused on an object 6 ft away
using my Mamiya 150mm lens. Camera was mounted on a sturdy tripod. Last time
I tried imaging with the Mamiya, I didn't yet own the FM60 and so I relied
on the prism + 2x magnifier. None of my medium format images came out in
focus.
For those of you unfamiliar with the FM60 focusing eyepiece, here is a link:
http://www.buytelescopes.com/container.asp?dest=/manufacturers/takahashi/fm60inst.htm
Question: should I go with the film plane result?
Thx,
-Phil
Phil:
The results you are getting are not unusual.
Achieving critical focus in astrophotography is more difficult than one would assume.
Is your intention to use the Mamiya and 150mm lens for wide field imaging or to use the Mamiya body at the prime focus of a telescope?
First I wouldn't use a target only 6 feet away. You should pick one nearer to infinity, which for a 150mm lens could be "down the street" or as far away as possible.
Kent Kirkley
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