I am not an engineer, though a DIY sort of guy. Reading your "discourse" to
me is like opening a treatise out of the academe? Are you guys indeed
professors of some sort? Gee, I am amazed at the interest, time and effort
put into this knowledge journey. Nonetheless, my thanks and I am sure the
same coming from others for the enlightening exchange.
Regards
Titoy
----- Original Message -----
From: John A. Lind <jlind@xxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Thursday, January 18, 2001 5:14 AM
Subject: Re: [OM] Film to flange distance in various OM bodies
> At 23:07 1/17/01, Gary Reese wrote:
> >I'm not sure what unit of measurement the micrometer is calibrated for,
> >but it is a distance measure none the less.
>
> The information I found some time ago gives 46.0mm as the nominal flange
to
> film distance for the OM system.
>
> This distance is of interest to those adapting lenses from other systems
> and for astrophotography in adapting an OM to a telescope. For the
> purposes of this experiment, relative measurements are perfectly
> acceptable. I suspect the "ancient" micrometer measures in inches. To
> make an absolute measurement of the distance you would have to "zero" it
to
> a dead flat surface . . . or at least record the reading on a dead flat
> surface and then use that as an offset for the delta.
>
> I agree your results do not support any hypothesis of variation in this
> distance among the bodies you measured! Indeed, the distance appears to
be
> high precision . . . which is very important for high sharpness at
critical
> focus. I have read that tolerances for flange-to-film on a high-end
camera
> body are usually in the range of a couple ten-thousandth's of an
> inch. This is supported by the shop manual I have for a ZI Contax IIIa.
I
> was shocked when I first saw the tolerance for it. After some thought
> about it, I realized why. For 24x36mm film frame to exhibit extreme
> sharpness of the critical focus region when enlarged to about 10X for a
> large print, or about 35X for slide projection, this distance must be very
> precisely set.
>
> All the more reason for us to care for our OM bodies, and protect the
> flange and back from damage.
>
> Thanks, Gary, for taking the time to conduct your test!
>
> -- John
>
>
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