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Monday, April 27

Pre-exposure follow-up


Being an inquisitive sort, I went on to Google+ and the Analogue Photography Users Group and posed much the same question on the topic of Bruce Barnbaum and Barry Thornton, who's right and who's wrong, as I featured in my last post.

Cutting to the chase, the consensus seems to be that Barry and Ansel Adams, both of whom believed in the efficacy of pre-exposure as a way of improving shadow detail, are right and Bruce Barnbaum isn't.

Just to recap, Barry and Ansel were proponents of pre-flashing negative material in camera to improve its response to deep shadows and Bruce thought it was bunkum (Is that still a word? Haven't heard it for ages. I hate it when perfectly good words fall out of usage whilst others are introduced to the language and accepted. "Alright" is one example and it's about as all right as alwrong is).

Brutal!

There were a few comments left after the blog post that seemed supportive of Barry/Ansel and a whole lot more on APUG. One commenter there was straight to the point. "Just another case of Barnbaum being wrong," he wrote. Ouch!

The APUG thread makes for interesting reading if you like that sort of thing. It's now ten pages and 96 comments long and is beginning to get quite technical. Here's the APUG link. I'd say a big majority of the comments were supportive of Barry/Ansel but I haven't actually counted them. See what you think yourself. There isn't much being written that backs up Bruce's forthright claim that, "Some well-intentioned practitioners advocate the use of this technique. In large part, they are wrong."

I posted about the same subject on some Google+ groups and the discussion went much the same way. No one really sides with Bruce but there are more than a few who think that it's all a bit too much of a bother. I sympathise with that opinion but I was interested in the issue from a technical point.

When flashing, does length matter?

One Google+ member, Oshi Shikigami said he was working from memory but had this to say, "One thing not mentioned is the length of time between flash and exposure. Film will work to some extent pre-flashed, IF it is not too long between the two exposures.

"The film will eventually "recover" from the pre-flash, if it is not then exposed. Think of a static charge on a piece of plastic. It slowly dissipates until it is essentially like it was before any exposure. (This comparison is not literally true, just a way of understanding the concept)." Very interesting.

Ansel moments after pre-flashing a sheet of film - well, could be...

So, based on all these replies from photographers with an opinion, others who have read the same books I have and those who have actually done some testing, I think it's fair to say that pre-exposure or pre-flashing is a useful tool to have at your disposal if you're a roll film user and can't give individual frames bespoke exposure and development.

No bother

As pondered earlier, just how useful it might be and whether it's worth the trouble is up to the individual photographer to decide. Certainly, from a practical point of view it doesn't really seem like much of an effort to make.

If your camera is on a tripod and has a multi-exposure facility then it's the work of just a minute to pre-flash a frame before making the actual exposure. You can always do one without the pre-flash just in case you're worried it might not work properly.

Will I be using it? I might, I suppose. A little, plastic diffusion disc takes up virtually no room and adds no noticeable weight so it wouldn't do any harm to at least carry one so that I have the option should the mood - and the light - take me.

4 comments :

Petros Gkotsis said...
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Petros Gkotsis said...

I have both Ansel’s and Bruce’s books and have been puzzled with this although I never really tried testing myself. Bruce also advocates the use of zone 4 for zone system photography instead of zone 3- it seems in general that he is a firm believer of overexposing films to get dense negatives in order to be able to “print texture and not just tones”. He says for example that when determining your “personal” film speed it is good practice to always take as final speed half the iso you have calculated from testing to err to the safe side, while others say that when unsure just keep the lowest of the values you get. I don’t know if this is the reason for his different views on the issue of pre-exposure. I also have the darkroom cookbook by Steve Anchell where he presents 4 methods to increase film speed: by exposing to forming gas before exposure, by exposing to a green lamp for 40 min after exposure, by using special cameras with LEDs flashing the film during exposure, by exposing to hydrogen peroxide fumes during development and finally by using additives in the developer- although he refutes the efficiency of this method. Could LEDs provide a similar effect to pre exposing the film to light? I don’t know. I guess only testing can provide evidence to clarify this.

DavidM said...

Michael Langford's Advanced book recommends the neg flashing on page 166, but give no details.

DavidM said...

By coincidence, I came across a friend's copy of Beyond the Zone System (Phil Davies). The books printing is not really good enough to illustrate some of his points, alas, but he does describe juggling exposure, paper grade and flashing for a print.
About film flashing, he points out that not enough has no effect, but too much has the effect of greatly reducing contrast in the shadows. He seems to be implying that there's a very narrow window for the optimum effect with film flashing. Perhaps this is the origin of the idea that it doesn't work – an improvement in shadow detail being swamped by a loss of shadow contrast. He also claims that it gives a small increase in film speed, but this is by reference to the resulting shape of the toe rather than by examining rival prints.
Of course, he writes before digital imaging became so common. Today, careful scanning might rescue the low-contrast shadow detail, but this will not please the darkroom purists.