Well since none of you knew, or cared or were able to "fill in" I had to put
the old grey cells into thinking mode and developed a method to test the
IS/L B Macro diffuser's screen exposure reduction factor myself.
The method involved a tripod mounted OM-4, F280 flash, 200/4 Zuiko (has the
same length and filter thread as the 35-180), TTL Auto Connector T20
(allowed me to put the flash on a second tripod), a TTL Auto Cord T and a
neutral grey card as the subject, put at the same distance where the
IS-3000+converter can focus, which is about 50cm. from the film plane.
First I searched for the correct exposure limit with this setup, without the
diffuser, and the flash -put in TTL OTF Auto Mode and set sideways from the
camera to avoid lens shadow- and found it at F22, ASA 50. Correct exposure,
btw, only based on the Auto Check LED and not on slide evaluations.
Then I attached the diffuser and put the tripod mounted flash right behind
the camera, with the flash head at the same height from the lens where the
IS-3000 has its flash head (very low compared to the F280!).
With the latter setup I had to open up the aperture by three stops, so this
is the diffuser's exposure reduction factor. For presumably correct Super FP
exposure I extrapolated the Super FP graph that's printed in the IS-3000
manual to a 50cm distance, and subtracted three F-stop values for each
shutter speed. This gives for ASA 400:
1/2000 - F5.6
1/1000 - F8
1/500 - F11
1/250 - F16
1/125 - F22
For ASA 100 of course subtract another two F-stop settings and count out the
1/2000 setting. Yesterday I did a bracketing test at 1/1000, 400 ASA for
each aperture full stop on an exotic plant with miniature flowers in bright
sunlight to test the above assumptions. Results yet to be developed.
I wrote : ---()
: Maybe some of you can help me with an alternative way for flash
photography
: on the IS-3000 with the achromatic Macro Converter IS/L B.
:
: The standard procedure according to the converter's manual is to attach
the
: diffuser screen to the converter, set the camera to Aperture Priority
Mode,
: and select an aperture according to the film speed: F11 for 100 ASA, F22
for
: 400 ASA.
: This method clearly has at least three major disadvantages: only one
: selectable aperture means no control of DOF, the 1/100 sync speed may
cause
: ghost images in daylight, and you can't use a film faster than 400 ASA.
:
: A much better method might be taking advantage of the Super FP
capabilities
: in Manual Mode. Thus you can use shorter shutter speeds to eliminate ghost
: images, and experiment with shutter speed and aperture to change daylight
/
: fill flash ratios and DOF.
: The problem however is that you still need to use the diffuser to avoid
: parallax and lens shadow. This makes manual FP even more tricky than it
: already is. My questions are:
:
: What would be the correction factor on the Super FP GN with this diffuser?
: Has anybody ever tried this, and if so, could he/she give some guidelines
: for proper shutterspeed / aperture combinations? This info could save me a
: lot of bracketing tests for every possible combination.
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