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Re: [OM] external metering with extension tubes

Subject: Re: [OM] external metering with extension tubes
From: Andrew L Wendelborn <andrew@xxxxxxxxxxxxxxxxxx>
Date: Wed, 30 Jul 2003 14:54:40 +0930
At 10:54 PM -0400 2003.07.29, Charles Sdunek wrote:
>Since i have two OM-1s an OM-2 and an OM-2n, all with light meters that need 
>to be recalibrated, I was wondering how you figure your exposure using a hand 
>held light meter when shooting through extension tubes.  Does anyone know a 
>formula for how many stops to increase exposure to compensate for distance 
>extended?


I did have some formulae but now of course can't find them!

Usual advice is to try a few bracketted shots.

And here there's a rule of thumb that says open up one stop for 20mm extension:

   http://homepages.ihug.co.nz/~mostert/macro                   0hotography.htm


I haven't done that though.

Our 2n also has a meter in serious need of re-calibration, but I did it myself
as below, set the  compensation as determined below, and then use TTL metering
for both natural light and T32 flash.

To figure out the error in the meter, I put some light onto a wall so that
there was an area of even illumination that filled the viewfinder. I then
metered that reading with both a friend's spotmeter, and our cheap reflected
light meter. They both had the same reading! I then set the compensation
on the 2n to agree with that. ( -1 1/3 stops -- not good.) I then repeated
with different lighting and confirmed the result.

I did this recently, so don't have many exposures yet to judge success.


Of course, others more expert at this might have different ideas ...


regards
  Andrew

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