I think what you need is the folllowing two formulae:
1 determine the reproduction ratio as lens extension divided by lens
focal length.
2 determine the exposure increase factor as (repro ratio + 1) squared.
Thus using a 50mm lens and a 25 extension tube, repro ratio is 25/50 = 0.5
Hence exposure increase factor for that set up is 2.25, which is slightly
more than 1 stop.
Look out for "Macro Photo & Cine Methods" by A & I Tolke Focal Press 1971
(or "Makrofoto/makrofilm" VEB Fotokinoverlag, 1965 which has plenty such
detail (but inaccountably misses out on any coverage of digital techniques).
--
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of usher99@xxxxxxx
Sent: 25 October 2005 22:50
To: olympus@xxxxxxxxxx
Subject: [OM] Re: WTB T28 Calculator Panels
Thanks for the links to the flash brackets. The T28 does not work well with
non TTL auto for OM-2---I found the instruction booklet on-line. Some of
the hardware can block the sensor and they say it does not correct for
magnification. My macro books all assume one is using dig TTL. I wonder
how to correct for extension tubes.
--snip
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