Preflashing film

[T3D Greg Erker <erker@xxxxxxxxxxxxxx>]

Suppose I want to pre (or post) flash my film to
reduce contrast slightly and bring out the shadow
details. How best to do it?

1) Probably the easiest way (if the camera is on
the tripod) is to place a diffuser over the lens(es)
of the camera and do a second exposure. Either stop
down the lens more or use a ND filter with the
diffuser.  Assuming no rapid changes in the scene
you are photographing you will end up with a "flash"
that is the average colour of the scene you just
photographed. Is this good, okay, bad?  Is a white
"flash" the best thing to do?

2) Use an electronic strobe with diffuser and
hold it over the lenses to make the "flash"
exposure. There would be some calibration required
to find the camera or flash settings (or ND filter)
to give the required small exposure.

3) Someone on P3D once talked about using a 45
degree beamsplitter (plain glass) in front of
the camera. The scene comes thru the glass virtually
unaffected and a diffused electronic strobe above
or below the camera simultaneously does the "flash"

[ ()\         (scene)
    *

Where [ is the back of the camera
() is the camera lens
\ is the plain glass BS
* is the diffused electronic strobe

  This still has the calibratio problems of 2
but allows one shot flashing if you rig up the
strobe and BS permanently.

4) On a medium format camera like a TLR or Sputnik
you could install small light bulb(s) which could
be wired to allow flashing to occur by connecting
up a battery for a certain length of time. Difficulties
include the colour temp of the bulbs (could use a
blue filter), evenness of the lighting, and
trial and error calibration to get the right
amount of "flash". (Saw this in Popular Science
a long time ago. At the time I wasn't into photography
and couldn't figure out how a light bulb would
help night photography.)

----
#1 is probably easy enough that I might actually do
it in the real world. As long as a non-white "flash"
is ok.  Hey, how about:

1a) Put pingpong ball halves over the lenses and let
the sun or ambient light strike them to give a white
"flash".

  I could almost picture myself doing 1a also.
---

Any other good ideas?

How much preflash is desirable?  I recall the number
of 5 or 6 stops below the exposure given to the film.

Thanks - Greg E.

(Just doing my part to keep this list alive :)



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