I've been reading about flash compensation on this list but it's not clear
to me what it means. I also cannot find anything in the manual of my MZ-5n.
Is it the same as fill-flash with the flash at lower output so it won't completely
fill in the shadows?
IMO, there are three basic reasons for flash compensation.
The first is simple - the flash is calibrated for 18% grey. If you are shooting something lighter than that you need to increase the flash, something darker, and the flash should be decreased. This is basically the concept of exposure compensation applied to flash.
The second is to use the flash for fill. If you manually set the exposure to be correct for the ambient light but want to birghten up the shadows, you need to adjust the flash power downward to avoid over exposing the parts of the image (the non-shadows) that would be correctly exposed without flash. Doing this lightens the shadows without significantly lightening the highlights, and you get the benefits of fill flash without the "flashed" look.
I use TTL flash at -1.3 stops for fill regularly for birds etc. Think of it like this - let's say your film or CCD can record 2 stops over and 3 stops under compensation (I'm used to slide film). That's 5 stops. The scene you are attempting to record has 10 stops of light, from deep shadows to the highlights. The camera meter pegs the exposure 2 stops under the highlights (good meter).
So here's what you got - the lets say that the shadows have 1 unit of light. With a 10 stop range of contrast you have 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 units of light from the shadows to the highlights. Your system is set to expose for 128 (two stops below highlights). To get correct fill flash, you need the flash to kick in something like 12 units. At this power level the flash lightens the shadows enough to fill them (you still loose 2 ev's to blackness but the rest actually appear on the slide) but has an inconsequential effect on the brighter areas of the exposure (e.g. the +1 stop areas go from 256 units to 268 - a barely noticeable increase.)
It's basically a kludge, but setting the flash to TTL and putting in -1 to -1.5 exposure compensation works OK. It's better to figure up the exposure and use a manual flash appropriately adjusted, but you can't do that in a lot of situations.
The third use of fill flash is to make up for problems in the way TTL exposure is determined. Let's say you take a photo of a brick wall that is 18% grey. It fills the whole frame. The TTL exposure should be dead on - the light from the flash hits the wall, bounces into the camera and off the film, the sensor reads it, and shuts it off at just the right instance.
Now lets say that the top half of that wall falls away, so the wall only fills the bottom half of the frame. The top half is inky black night. The light from the flash hits the half wall and bounces back into the camera. Compared to the hypothetical above, there is only half the amount of surface area for the light to bounce off of. So the camera patiently waits till the same amount of light (compared to the example above) hits the sensor, and then shuts off the flash. The result - the half wall is one stop over exposed.
Now imagine that one brick is just floating in darkness before you... Here the TTL flash exposure will be two or three stops over....
The newer P-TTL really does a great job of addressing this problem - technically I don't know how it works. But for older flash systems that use simple counterweighted metering, you have to use flash compensation to adjust for how much of the metering area is filled by the subject. Personally I just imagine the subject as melting and see how much of the frame it fills - a little off beat but I had a lot of experience watching things melt in the late 60's and early 70's.
The explanation (trick) about using manual mode and the exposure compensation dial for flash compensation, for what flash/body combinations is that. I just bought a AF360FGZ from ADORAMA (great shop BTW) and it has flash comp. on the flash so I guess I don't need to use the trick?
Nope - AFAIK the exposure compensation dial will only work with P-TTL exposures.
Hope this helps -
MCC
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Mark Cassino
Kalamazoo, MI
[EMAIL PROTECTED]
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Photos:
http://www.markcassino.com
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