Proper exposure with electronic flash is a function of flash-to-subject
distance. Period. Lens focal length is not a variable here. As you state,
simply use the flash unit's settings as indicated as a function of a given
F-stop. F/16 is f/16, no matter the lens' focal length. The distances
suggested on the flash are not only maximums, they are genarally very
optimistic maximums. I have measured and tested my flashes and they are all
about 200ver-rated. The auto circuity will quench the flash if it is
closer than the rated maximum.
Macro adds some complexity because you start to deal with extension and
magnifications and such stuff. For your 283, you need to figure these
compensation factors out for yourself. Here, beyond the excellence of the
optics themselves, the Oly OTF flash metering is so outstanding. Regardless
of the extensions, magnification, filters, or whatever else you have between
the subject and the film, the metering system will accurately meter the
flash exposure and cut the flash(s) off at the right instant for proper
exposure. Yes, it can be fooled into a wrong exposure, such as highly
reflective surfaces against a black background. But the ASA/exposure
compensation knob helps there. Oly offers a whole line of specialized flash
units dedicated to marco work. See Denton's web page -
http://www.dentontaylor.com/watch.htm -for an outstanding example of the
differences among them with the same subject
John P
______________________________________
Ted <tedconley@xxxxxxxxxxxxx> asked:
>Can someone explain to me the means of calculating the proper
>flash settings (F-stop, distance of camera &/or flash to subject)
>when the focal length is varied? When I first started shooting
>(an OMPC w/a 50mm lens and a Vivitar 283), I would simply use the
>flash unit's settings as indicated as a function of a given
>F-stop (i.e., at F16 I should be 10 feet from the subject). No
>problem here. And I also understood that if I added on my 2x
>teleconverter, I needed to add 2 stops more light. But how can I
>calculate the proper F-stop and distance to subject for ANY given
>focal length. I'd like to figure out the proper settings for my
>Zuiko 28 and 135 mm lenses as well.
>
>Also, is the distance suggested on the flash unit the maximum
>distance only, so that you could get as close as you wish and the
>flash's sensor will tell the flash to cut-off at the proper
>amount? Or is it the suggested distance as opposed to a mere
>limit on the amount of distance to subject? I want to take some
>pic's with a 50 mm macro at a few inches from the subject and I'm
>not sure if I'm just gonna end up overexposing my subject.
>
>Ted.
>
>
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