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What does it mean to set your flash -1 or -2 ?

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July 13, 2004

How (or if) you can control flash output level is dependent on the make/model of flash and camera. With non-dedicated automatic flash you can simply set ISO on the flash higher (- FEC) or lower (+ FEC) relative to the camera and film ISO. With dedicated TTL flash you may not be able to adjust it directly, or it may be adjusted by a control on the camera.

Typical indoor flash snapshot is taken with relatively high shutter speed (often the default of full program exposure modes), so the subject is well exposed, but the background is dark - underexposed 1 or more stops relative to the flash subject. In effect, flash compensation is 0 and the background gets -1 or -2 (or whatever) stops of exposure compensation.

With balanced flash or fill-flash, the aperture and flash output are set to properly expose the near subject, and the shutter speed (combined with the aperture) is set to properly expose the background. ==> 0 compensation to both flash and ambient exposures. In the well-lit outdoors, many people prefer less fill-flash on the subject, applying -1 or -2 flash exposure compensation. This is a more "natural" look as the subject is already well lit by the ambient light and the small amount of flash subtely opens shadows. This is done by decreasing the flash output, or by adjusting the aperture if flash output is manual and fixed. In Nikon-world I believe this must be set manually, but with Canon (and other makers?) TTL/A-TTL/E-TTL flash algorithms default to automatically apply negative flash compensation in bright settings (EV 10+). Pro-level Canons have a custom function to defeat auto fill flash reduction so users can set theri own level.

This all assumes typical average 18% gray toned scene. Just as with regular exposure compensation, you may feel compelled to apply additional +/- flash exposure compensation if the flash-lit subject is predominantly lighter (white wedding dress) or darker (black tuxedo), especially if you are shooting slide film rather than wide latitude print film.

I'm probably not explaining it as well as is done here, a site detailing the features and use of Canon's flash system : http://photonotes.org/articles/eos-flash/ (assuming you are the same Cindy who asked another question regarding dark wedding pics taken with a Canon Rebel and 420EX).

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July 13, 2004

Thanks again.

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July 14, 2004