On 8/12/2005 9:58 PM Mike spake thus:

Pretty much the obvious places, if you think about it a second or two: the end
flap and all edges. The least likely place is the dark slide.

The paper-fogging test isn't a bad idea if you can't trust your holders.

I've had light leaks as a results of not inserting one of my 4x5 holders far
enough until its ridge dropped into the location slot.

I have only Graphmatics that do not leak light, though there is a potential
for leakage if the felt that traps light where the dark-slide goes wears
out. Mine are quite old, and if they were going to leak there, I suspect
they already would have.

My Fidelity Elite holders would leak only where the dark slide goes in.
Unless the flap at the other end just plain falls off, I would expect no
leakage there. The tape is just a hinge. The ridges in the flap and holders
keep the dark from leaking out. I.e., pinholes in the tape would not matter
other than as a warning that you should replace the tape after a while.

If you do not insert the film holder all the way into the camera, with the
ridge on the holder fitting in the groove in the camera, light will leak there.

I find I fog the film most because those little hooks that retain the dark
slide are too loose and they move so when I pull the holder from the camera
bag, the dark slide comes out a little bit, and that little bit is too much.

The only place that I've ever had a film holder leak light was at the foam
where the dark slide enters the holder.

Why are you filling them with paper? They leak at the tape or sometimes
the dark slides get a small fracture. Or the inner surfaces develop a
pin sized scratch that you can blacken with a sharpie.

P.S.: I cut little notches with an XActo knife in the edge of my holders
(between dark slide and film) so they are numbered 1 to N in binary. That
way if there is fog, I can tell what holder and what side has the problem.

  The most common leak is at the light valve for the dark
slide. To check this use a flashlight. Remove the dark slide
and open the loading flap so you can look straight at the
slot for the dark slide. Even with a strong flashlight you
should not see light through the slot.
  Another source is a poorly fitting loading flap. The flap
has rebates in it that match those on the end of the holder
to form a light trap. When the dark slide is in place it
locks the flap. When the holder is in the camera pressure
from the back plate keeps the holder locked when the dark
slide is removed. If something has gotten under the flap, or
if the tape hinge is worn enough the flap may not close
properly. That can sometimes keep the holder from seating
correctly in the camera or keep the dark slide from going in
all the way. I have had this happen but its pretty rare. As
long as the tape hinge allows the loading flap to move
around lengthwise, it is not a source of trouble. Its only
function is as a hinge, its not supposed to be a lightproof
seal.
  Calumet has original hinge tape available but nearly any
fabric tape will do.
  It is also possible (but rare) for a badly warped holder
to cause a leak but such an extreme warp will be visible
especially if you sight along the holder.
  Another problem is failure of the holder to seat
correctly due to some problem in the camera. The best way to
find this sort of leak is to put some white paper in the
holder and put it in the camera. Then remove the lens board
and shine a light all around the back. If here is a leak
this will usually show it up.
  Note that there may be other leaks in the camera
mimicking a holder leak. Check for pin holes in the bellows
or leaks in the lensboard. Sometimes putting the light
inside the camera will show up leaks that do not show by
inspecting the inside.