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Old August 4th 04, 06:10 PM
Alan Browne
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Default Ghosting Problem

Justin F. Knotzke wrote:


Cool shot.

This ghosting and complete white out appears to be happening because the
D-MAX of my film is being reached. Note that the arms of the rider in orange
appear where the tree nicely appears in the background.

They both have different color values (green/orange)... different
layers of color were used. Where the "white patch" shines
through is the same as the white sky in the BG. (all three color
layers react to white). (This is why when making multiple
exposure motion studies a black (or other dark) background is
usually used).

Just so everyone knows, this isn't the effect I was going for. ;-) I was
hoping to get some rear curtain sync blur going but not having my subject's
face rubbed out..

Well you do have some. Note that for a face to be well exposed
in a moving shot, the background must be dark. The lighter the
background, the less there is "left over" to record the flash
frozen subject.

If my assumption is correct, my thinking is that I need to decrease the
exposure by a stop or maybe more and then increase the flash output by a stop
or more.

Maybe. Notice how the redbrick buildings are already a bit
underexposed? Reducing the exposure will turn the buildings and
the trees to silhouettes. Flash? You can bring it down a stop
with the effect of the background bikers looking only like blurs
(no stop motion effect as is already evident in shot 13), and the
foreground bikers will maintain the strobe freeze). If you
increase the flash, you will get really high values and
reflections (note the skin highlights of the nearest biker on
13), but the background bikers will be more 'frozen'. Your choice.

The real issue here is the background needing to be dark enough
to not saturate the film where you want the bikers to be frozen.
If you reduce the exposure, then "white" sky will become greyer
and the trees/buildings will tend to silhouette. Solution:
capture the bikers where the BG is naturally dark.

Assuming this is all correct, is there a way I can figure out how many
stops I need to decreate exposure and increase flash exposure by?

As you're looking to have a "normal" looking BG, you need to
expose for it ... the flash will not help with it at all.

Since flash does not care about shutter time (as long as you make
sync speed), then think of it all in terms of where you want your
speed for the blur effect (about 1/30 to 1/15 in this case?)
and then set the aperture for that speed to expose the background

I was thinking of maybe metering the sky, then metering the subject and
using the difference as my compensation factor..

Slide film? If you meter a white sky, then open up 1.7 to 2
stops (of aperture as your speed is predtermined for blur in this
case), if you meter a blue sky, then 1 stop will do. That will
give you the non-flash portion of the image.

The flash portion of the image is dictated by the TTL flash
system. Assuming you're using the F5, this should be minimally
complex and there should be little reason to flash compensate
with these subjects... in your shots the jersey reds are nicely

I like your series of cycling shots, BTW!


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