Pre-exposure techniquesgreenspun.com : LUSENET : Large format photography : One Thread
I have been using LF for a short time, and I have been reading a few articles concerning pre-exposure for transparency film. Two methods have been proposed: a white card or white plexiglass. Any preferences? Mention has been made of pre-exposing for Zone II or III on some film before leaving home, and others have done the pre-exposure on-site with the camera in the position needed for the shot. Which is the better alternative? If one decides to pre-expose on site, what is a good step by step procedure? Specifically,should you pre-expose focused at infinity before setting up any needed camera movements, or is it ok to set all movements and then pre-expose before the final exposure. Thanks
-- Winston Chaffin (firstname.lastname@example.org), March 08, 1999
I don't shoot transparency film so keep this in mind. I use pre- exposure when needed but for me it is always a post-exposure. At least with black and white film, the film remembers all of the exposure it has teceived even it is below the exposure threshold. So when you add the exposure later, all of the details show up. This may work in color, it is certainly more convenient to be able to work under controlled conditions.
-- Jeff White (email@example.com), March 08, 1999.
This technique is called 'flashing'...to (in B&W) suppress the upper end of the film curve. In color...? Just make sure (fer sure) that whatever light source you use matches the color balance of the film, if you don't want special effects. I believe..(if I recall correctly) that I used to flash B&W under my enlarger with each sheet loaded in a holder. I had a system worked out where I used a fairly heavy ND filter over the open holder..and a certain time @ a certain aperture. The idea is to build up just a little bit of base density (fog).
I once shot a job with Ektachrome all loaded in my darkroom with my new stereo blasting. The little red 'on' light on the amp didn't bother me until I looked at the film later. Interesting red color cast all over everything..jewlery, as I recall. The highlights had a lot of detail, though.
-- C Matter (firstname.lastname@example.org), March 09, 1999.
I've used pre-exposure with Velvia to cut down the contrast. It works quite well up to about 1 stop of reduced brightness. On the occasions that I use it, I set up the camera with all movements, focused properly and simply adjust the shutter speed so that the pre-exposure is done at 4 stops under. I have read of others using 3 stops so you might want to experiment in this area. I use a white card now but simply used the white side of my darkcloth before I switched to the BTZS cloth. Don't worry about being focused at infinity as you can hold the darkcloth or card fairly close to the lens (in front enough so that light hits the card) and this will render it as an out of focus subject. If you were shooting a macro subject, then, naturally, you would want to focus to infinity before pre-exposing.
-- Mike Long (Mike-Long@excite.com), March 09, 1999.
I use Velvia in 4x5 and set up for the shot in the normal way. I then take my gray card and meter it. This gives you a zone 5. stop down 3 1/2 stops, which now gives you zone 1 1/2, hold your gray card as close to the lens as you can without casting a shadow. Boink. Now shoot your shot as you normally would. I don't flash in the darkroom whether pre or post because I want to do the adjustments in the field to tailor the pre-exposure to the lighting situation. Sometimes it only takes 1/2 stop and sometimes it takes 2 stops. And if you have one of those guchi translucent filters (cokin or lee) it helps with color balance real well. You can even pre-expose at 3 stops and under develope the film and make a 7 stop scene printable. But you need to experiment with your equipment and shooting style. Practice makes perfect. Try it. James
-- james (email@example.com), March 12, 1999.