IMAGE SPILLING OUT INTO FILM EDGE

greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread

I'm sort of new to this game and have noticed that areas of strong highlights - high density areas (?) - on my negatives (APX100 in Rodinal at Agfa recommended time/temp/agitation) had "leaked" into the film edge. It didn't show on the print (it was outside of the frame of course) but I was wondering whether this "leaking" is normal or indicative of a processing error on my part that is perhaps affecting the highlights actually in the frame? If the latter, suggestions for improvements please! Thanks.

-- Ian Hay (ianhay@aeolos.com), October 26, 1999

Answers

This is quite normal. You may also notice a spillage from highlight areas into shadows, especially over high-contrast boundaries. You can reduce this by giving less exposure, or reducing development.

-- Alan Gibson (Alan.Gibson@technologist.com), October 26, 1999.

The effect is called "piping." It is the result of the high intensity light which strikes highlight areas of the film bouncing back and forth off the front and back surfaces of the film (i.e., within the thickness of the film) in a kind of lateral zig-zag motion to adjacent areas of the film. to minimize it, take care not to overexpose. njb

-- Nacio Brown (njb@limn.net), October 26, 1999.

The film actually act like an optical waveguide, just like the fibres used in medical endoskopes. When a light ray passing through the film hits the film/air interface, a little light bounces back into the film following the rule angle incident = angle reflected. Film manufacturers provide their films with anti-halation backings to keep the amount of light reflected back small, because the reflected light impairs the image sharpness. (You can study the effect with Kodaks IR film. This one has no such backing, and the effect is so strong - and the film so sensitive - that you must not even put it in your camera w/o a changing bag, because the film acts like a waveguide to an extent that several negatives may be fogged.)

-- Thomas Wollstein (thomas_wollstein@web.de), October 28, 1999.

Moderation questions? read the FAQ