Hi Gordon How long does the effect last? Can I flash a bunch of film or do I have to do it pretty much just before I use it sort of like a wet plate? thanks andy
-----Original Message----- From: pinhole-discussion-admin@p at ??????? [mailto:pinhole-discussion-admin@p at ???????]On Behalf Of Gordon J. Holtslander Sent: Monday, November 04, 2002 11:16 AM To: pinhole-discussion@p at ??????? Subject: Re: [pinhole-discussion] large format ortho Hi: By providing a longer range and shorter exposure times, preflashing the film allows ortho to record shadow details much more effecctively. I use an enlarger, and an exposure timer to do this. Its just about the only thing I use an enlarger for now :) I set the enlarger so that it will expose an area larger than the film I use. I stop it down. To determine the flash duration I did a series of test exposures until I found the longest exposure that would NOT fog the film once it was developed. With my setup and developer its around 12 seconds. If you don't have an enlarger you may be able to do something like turn on a very dim light - a 7 watt nightlight or something like that for a few seconds. You essentially have to be able to illuminate the film under a very low light level for an accurate amount of time. The amount of time is determined by finding the longest exposure the film can tolerate without fogging. If you don't have a really accurate timer, you would have to use a dimmer light source and expose it longer. I could probably get away without using my timer, and use my wrist watch, or count to 10 etc. (all of this can be done under safelight) The film acts like it has a threshold of exposure. No latent image will be formed until the exposure level has surpassed this theshold. For pinhole this means that while taking the picture, some time is spent simply getting past the threshold without recording any image information. If this theshold is surpassed prior to exposure (by pre-flashing) the exposure times will be shorter - resulting in a "faster" film. ...snip
