Hi: It seems to last for a while. So far I think I've preflashed film and shot it a week later and had good results.
I'm testing this now :) - Its getting too dark here for pinhole shots by 5:00 pm - Since I work till then I'm only shooting on weekends. Since I have young kids I'm very busy weekends :( . I have some film that was flahsed last month in a camera waiting to be shot. If the pre-flashing acts like a normal latent image - it could last for years. Last year I found some sheet film holders with film. Turned out to be shots taken 8 years ago. They turned out fine. :) Gord On Mon, 4 Nov 2002, andy schmitt wrote: > 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 > > > _______________________________________________ > Post to the list as PLAIN TEXT only - no HTML > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/ > --------------------------------------------------------- Gordon J. Holtslander Dept. of Biology hol...@duke.usask.ca 112 Science Place http://duke.usask.ca/~holtsg University of Saskatchewan Tel (306) 966-4433 Saskatoon, Saskatchewan Fax (306) 966-4461 Canada S7N 5E2 ---------------------------------------------------------
