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Old Feb 23, 2009, 10:18 PM   #1
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I was given a brand new Bower 724AF TTL flash as a gift. The paperwork says it is compatable with Nikon F4, F5, F50, F55, F65, F70, F90, N90X,F401S, 601, Pronea 600, F801. It is a TTL unit. (Also fits Canon, Minolta, and Pentax)

Would this unit also be fully TTL compatable with a Nikon D40?

I tried the unit, and it seems to work, but it seems to have a limited TLL auto range, meaning that if I have my D40 set to manual and properly expose a subject about 15 feet away, it gives proper exposure if the subject moves 5 feet closer or 5 feet further away, about a 10 foot range, but it over exposes if the subject moves up to say 5 feet.

Perhaps the 10 foot exposure depth range is just the exposure latitude of the camera, but other auto flashes that I have worked with would always expose correctly from the maximum distance as close as a foot or two by quenching the flash duration to reduce light output.

This is why I wonder if the flash is actually functioning TTL, or does it just have a limited range?

Your thoughts and comments are MOST appreciated.

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Old Feb 24, 2009, 9:53 AM   #2
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It's probably not compatible with your camera.

Digital cameras use a different approach to flash metering, since the sensors in them are not well suited for metering from during an exposure (in the way you would using off the film metering during a flash exposure).

Flash systems for digital were redesigned to use a metering preflash instead (barely noticeable since it's very short and occurs very close to the main flash). Based on how much reflected light the camera sees from this metering preflash, it decides how long the main flash burst needs to be for proper exposure.

Flash systems must understand the newer commands in order to work properly with digital. Nikon refers to this as iTTL for their dSLR models.

Chances are, your flash is always firing at the same power level. So, you'll need to adjust your camera settings (ISO Speed, Aperture) to give you a brighter or darker exposure based on your distance to subject with that type of flash.

You'd be better off using an older Auto Thyristor type flash like a Sunpak 383 Super with Manual Exposure instead. At least the flash would have a sensor to measure reflected light during flash exposure and terminate the flash output when enough light is seen for the aperture and ISO speed being used (so that you wouldn't need to worry about changing camera settings with distance to subject like you would with a flash always firing at the same power level).

But, your best bet would be to get a Nikon flash that's fully compatible with your D40. If budget permits, the Nikon SB-600 is a very nice flash.

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