On Tue, 6 Jul 1999, Mickey Trageser wrote:
>I have a couple of questions. 1. Is it ok to use a Vivitar 283 with an
>OM-10?
More knowlegeable folk can take this.
>And 2. Does anyone have a link to a site that explains the meaning of guide
>numbers for flash units, and how to manually figure aperture settings
>appropriate to the film speed and guide number?
I don't have any specific URLs in mind, although under the photo section
of my page (link in sig), you'll find many wonderful sites. That said,
here's how to calculate aperture:
1. you flash has a guide number, say 104 feet for T32; this is for 100ASA
film; for 200, multiply 104 by 1.4. Each time you double film speed,
multiply guide# by 1.4
2. focus to subject;
3. read distance off of lens marking;
4. divide guide# by distance to get aperture.
5. fire away as flash recycles! A thing to note: since you are calculating
aperture for a full power flash, you MUST wait till you can't hear the
oscillator whining, which may be a some seconds AFTER the readylight
comes on.
Example: subject at 10feet, ASA100, T32 gives aperture of
(104)/(10) --> ~f/11
Eg. subject at 50 feet, ASA400, T32 gives aperture of
(1.4*1.4*104)/50 --> ~f/4
This is assuming full flash output, not auto range setting where you set
the indentical aperture on flash and lens. If you have a normal auto
setting, then the procedure is as follows:
1. set film ASA on flash unit;
2. focus on subject;
3. read distance marking, say xyz feet;
4. set flash switch by the distance corresponding to xyz feet--there will
also be an aperture for said distance;
5. set aperture on lens as indicated by flash and shoot as flash recycles.
Unless you're shooting at large distances with large lens openings, you
don't have to wait for the oscillator to stop; as soon as the readylight
is on, you can go.
>Thanks to any responder. I enjoy having access to such a wealth of
>knowledge, opinion, experience and feeling for the Olympus systems.
I hope that I could be of some assistance, and that I, as resident Cheeky
Whippersnapper, didn't commit any blunders in above explanation. Best,
/Acer Victoria
--
"Strong in the heart, weak in the flesh...." --Def Leppard
"video meliora proboque, deteriora sequor." --Ovid
http://student.ucr.edu/~siddim01/ <--don't visit just yet!
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