Re: [OM] T-10 vs T-28 flash?

[timberwolf]

Wrote Buddy Walters:
>When, Where do you choose between the T10 and T28.
>I understand the shadow idea, but I would be interested in how you choose
>between the 2 flashes and for which subjects, lens, preferences, etc.

>My interest is mostly Nature - for macro - insects (fly fishing).  I have
>noticed some overexposure in TTL if the subject does not fill a large
>percentage of the frame.  I've been thinking of trying to use the flashes in
>Manual mode.

For many years, I did all my macro flash work with an OM-1 and manual
flash. This is really very easy, as long as the spatial relationship flash--
film plane does not change. This means that as magnification (extension)
directly governs object distance and flash distance, exposure becomes a
direct function of magnification! When you know this function, all exposures
will be correct, irrespective of object reflectance, background etc.

It is quite easy to determine this. Let us say that you are using the 80 mm
Macro with the variable tube. Then you have the major magnifications
2:1 (half scale), 1.5:1 and 1:1 (full scale on film). With slide film, make a
number of bracketed exposures (varying apertures) of a standard target of
about 18 percent reflectance (equal to the medium grey Gray card),
remembering to record accurately each exposure at each magnification.
Evaluate the slides on a light table. With a minimum of luck, you should
find one exposure at each magnification which is at least in the ballpark.
You can fine-tune later, on the same target. If you got it all wrong, you will
at least know in which direction you erred, and by about how much.

With access to a flash meter, it is even easier. Focus on the white light
receptor hemisphere and fire. Say that the magnification was 1:1. This
means that the value you got has to be corrected for the light loss caused
by the extension, by opening up 2 f-stops. And that is the aperture you
will use hereafter, rain or shine, on anything. Here are compensation
values (extension factors) for different magnifications:

1:4..............+ 1/2 f-stop
1:3..............+ 3/4
1:2..............+ 1 1/4
1:1.5...........+ 1 2/3
1:1..............+ 2.0

Note that these factors are the same irrespective of what camera, lens
etc you are using. They hold for 4x5 studio cameras and for 35 mm
equipment, and whether the extension consists of bellows, rings, tubes
or the remains of toilet paper rolls. This constancy is especially welcome
when you are chasing running targets as I did (hunting spiders and
grasshoppers). I simply kept a card with the aperture for each standard
magnification taped to my flash.





Hälsningar/Regards
Lars Bergquist
Timberwolf Type, the independent
specialist in text typefaces - visit me at
<http://www.timberwolf.a.se/>

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