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rydolan
03-05-2012, 09:22 PM
I was wondering if anyone could shed some light (groan) on the internal workings of the top part of most sheet film holders. I'm talking about the part that holds the mechanism which keeps the holder light tight while the dark slide is being removed. Do they have a little spring loaded door of some kind? Are they built redundantly to help with light tightness? I'm sure every company has their own little nuanced way theirs works, but I'm just curious about the general concept.

Thanks much

Oh, one more thing... Why do they have that characteristic notch in the frame around the film? The one you can see whenever you develop the film.

JoeVanCleave
03-05-2012, 10:15 PM
Someone can correct me if I'm wrong, but my understanding about how the light seal on the dark slide slot works is that it uses a double row of felt material. Basically, there are two rows of felt-like stuff that pinch the dark slide front and back, one behind the other, such that when the dark slide is partially inserted there's at least one double row of material that's always sealing off the insides from external light.

As for the notch in the film, I'm not sure of its origin, but it's used these days to tell by feel which side of the film is the emulsion side (with the film oriented in the portrait direction, the emulsion side is facing you if the notch is in the upper right or lower left corner). The notch was also coded by a particular arrangement, used typically by Kodak, whereby the style of the notch could identify the particular film emulsion. You can see these notch codes listed in old film processing books. I believe Ilford and Fuji films still use notch codes, but not sure about some of the eastern European films (they still have notches identifying the emulsion side, but may not be coded to identify particular emulsions).

~Joe

jon.oman
03-06-2012, 10:46 AM
I had a broken 8x10 inch Lisco holder. There is an inverted V of springy metal at the top center. This is covered by black felt. The metal puts pressure onto the dark slide as it is moved in and out. The opposite side has a felt covering.

rydolan
03-06-2012, 01:15 PM
thanks for the info.