Re: [APML] Pre-Flashing Slide Film

["Jeffrey C. Schotland" <jcsphoto@qni.com>]

Chuck Vaugn wrote:
> Pre-flashing has been known for a long time but was basically given
> up on when gas hypering came along, in part because it is more difficult
> to do correctly than gas hypering. If I remember correctly, it also didn't
> show any particular advantage over gas hypering. If pre-flashing had a
> real advantage over gas hypering we'd all have setups to efficiently
> pre-flash our film. Lumicon would be selling preflash equipment instead
> of hypering tanks.

Well if Lumicon held a patent on preflashing, then they would be selling
that equipment. :)


Using fluorescent to preflash is a bad idea. The idea of preflashing is to
add a NEUTRAL base density to the film. Fluorescent light (cool-white) is
green and requires a color correction of 30cc of magenta to correct.

Fluorescent is an intermittent light source rather than continuous, it
cycles on and off 120 times per second. For approximately 30-40 percent of
it's cycle it generates little light and this light changes color
temperature as it reaches peak output.

Any shutter speed higher than 1/120 of a second is only going to capture a
portion of the cycle. You could actually end up grossly over or
underexposing your film depending on the moment of exposure during the
output cycle. 

A better choice would be to use a portable flash unit. It is color balanced
for daylight film. If you cannot adjust the output of your flash you can add
neutral density filters to the flash unit to reduce it's output.

Jeff

______________________________
     Schotland Photography

    Jeff@SchotlandPhoto.com
______________________________


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