Pre-exposuregreenspun.com : LUSENET : Large format photography : One Thread
I am interested in using pre-exposure in order to control the overall contrast range of a 4x5 negative, and I want to check that my logic is correct......if the Zone V exposure is, say, f32 @ 1/15s, does that mean that a Zone 2 pre-exposure is f32 @ 1/125s? Could I effectively achieve this by using an 8x neutral density filter, with some plexiglass to diffuse the light evenly across the film?
-- fw (firstname.lastname@example.org), April 26, 2000
No need that I can see for the 8x filter. Just reset your exposure to zone 1 or 2 depending on what the shadow looks like and place a piece of frosted or white plexiglas over the lense. You can make a piece of frosted plex by sanding it with a fine sandpaper until it is uniform in it's light distribution. I would couple this pre-exposure to a minus development scheme. You don't say what the contrast range is for the subject you are pre-exposing. When I have a decent contrast range across most of the scene but have a small area or areas that are going to expose with too little density, that is when I use pre-exposure or when the SBR is just too great for minus development alone. Of course you can use it for chromes also, so your beginning assumption is correct though I wouldn't bring it up past zone 1 1/2. Let us know how it went. Others could use this proceedure and would benefit from your trials. james
-- james (email@example.com), April 27, 2000.
James, thanks for your reply. I don't have a specific problem right now, I'm just trying to get the logic right in order that I can develop a different approach to something like an N-2 contraction . At present, for such purposes, I would rate TMax 100 at something like ASA32, and give 40-50% reduced development. Although this works, it would be useful to be able to use a higher film speed, and still be able to manage a contrast range of 7+ zones, and I wanted to be sure that I had understood Adam's comments on pre-exposure in "The Negative". I must admit I hadn't thought of its application for reversal films - that could be very interesting! I had thought that it might be a way to tame the contrast of Technical Pan, and achieve a reasonable speed with this film - what do you think? Regards
-- fw (firstname.lastname@example.org), April 27, 2000.
I've pre-exposed by placing a grey card in front of the lens (but not focussing on it) and have had decent luck exposing as high as zone III. Local shadow contrast suffers (at least in comparison to zone I or II exposures) but in situations where that doesn't matter, it gives you a gratifying bit of substance in the shadows. I just reset my exposure to place the preexposure at the desired level. Good luck. DJ
-- N Dhananjay (email@example.com), April 27, 2000.
As far as taming Technical Pan film, shadows aren't what need taming. The density of the high values is where the problem lays. For the way I use pre-exposure I gain about 1/2 stop of substance in the deepest shadow areas. I don't use it for large areas or large changes in density in those areas. I use it for say forest scenes or rocky areas where a lot of the shadows are lit by blue skylight. These small areas are hard to get detail into but I feel look empty and unfinished without a hint of substance in them. I have an image taken at 12,000 ft in the White Mnts. of a cliff face with a wall of dead Bristle Cone Pines reaching for the sky. The trees are dead and look like flames of silver shooting up along the ridge line. The cliff face is composed of ledges of white rock jutting out one atop the other with lots of shadows underneath. This is where I mostly use pre-exposure. Without the pre-exposure all the tones are compressed and the mid tones become muddy. I lose the sparkle. The subtle highlights are compressed even further. With a Z1 pre-exposure that doesn't happen. There is a hint of something underneath the ledges without sacrificing the midtones and Z7.8-8.2 highlights. In deep forest it is the same thing. All shadows are lit by blue and green light and very little shadow detail is gotten unless you pre-expose. For city or urban scenes, I use it to get detail under cars and in deep doorways. Try it and you'll put it in the bag of tricks. And it works great on chromes as long as you keep it to Z1.5 or lower though I have used it at Z2 when a color shift didn't matter. James
-- james (firstname.lastname@example.org), April 28, 2000.
As for TechPan, the reason the speed is so low is for developing shadows in the first place. Techpan is a scientific film used for strictly extreme contrast. Line drawings and bringing out detail in faint images like microscopic images. Stained tumors and the like. It has extremely fine detail when used like that. What you are trying to get the film to do when using it as a pictorial film is flatten the curve. I think I have that right. A more than normal contrast scene is a hard but not impossible situation to deal with using Techpan. Extreme dilution is requiered and almost no agitation. That will give you an N-1 and pre-exposure will boost the shadow detail up from Z2 to Z2 1/3 to Z2 1/2. That's about as far as you can take it and still keep your midtones separated. All zones higher than Z6 are achieved through developer strength and agitation. Hope this answers your question. I'm better with a picture in my hand than words. Let me know if I can help you with this more. I use both Techpan and pre-exposure a lot in my landscape work. And I am now using Techpan for flowers and still life work. James
-- james (email@example.com), April 28, 2000.
I'd like to try the pre-exposure with sunrises on chrome film. You know the story...not enough range on the film to get the shadows adequately exposed if you put the sunrise on Z VII. Let me see here...I would pre-expose a gray card or rough plexiglass and place it on zone 1 or 1.5. I'd then place the sunrise highlight on VII as usual, without compensating for the pre-exposure? thanks...
-- John Sarsgard (Endive4U@aol.com), April 28, 2000.
You ignor the pre-exposure. It is boosting the shadows by getting the film to the threshold of exposure. James
-- james (firstname.lastname@example.org), April 29, 2000.
Thanks for your comments, which I have found very helpful. The situation you described, of sunlit scenes with quite hard shadows, in which you want to retain some detail, is pretty much what I had in mind as the generic "problem" scene, and I will try out some pre- exposure over the next few weeks.
I haven't replied earlier as I have been away for a week hiking in Haleakala, and I could have done with some tips on pre-exposure when photographing the crater! I mainly use TMax100 in 4x5, and Pan F+ in 120, and Velvia in both formats. Up till now, I have been developing in Rodinal, and altering both film speed and development time to suit various contrast situations. For the first time, I shot some duplicate negatives and developed them in PMK Pyro, using the film speeds I had already calibrated for Rodinal with these films. The results are truly breathtaking - Rodinal is very good, but it is obvious that the tonal range and local contrast available with Pyro is greater.
-- fw (email@example.com), May 07, 2000.