When you use B&W film, are you as obsessive with exposure as with a slide film. or do you expose a bit extra over the meter reading? I have read in Photo Technic that it may be Ok to overexpose even by a couple of stops!! I would appreciate any helpful suggestions. Hasan

-- Hasan Ali (Hasan2@msn.com), September 25, 1998

Answers

Exposing any negative film is different than exposing a positive film. Positive films subtract density with exposure, so too much exposure or not enough exposure will leave you with an unacceptable image. Negative films build density with increased exposure, so the important thing here is to make sure the needed detail makes it to the film. "Accurate exposure" is an industry developed standard for comparing films and getting a generally good result. If more exposure gives you a better negative or finished image, is it really overexposing?

-- Jeff White (zonie@computer-concepts.com), September 26, 1998.

I usually hear this sort of comment from slide shooters; that for print film your exposure can be off by X number of stops because you can make up for it during printing. I have always found this advice to be flawed since it encourages sloppy exposure. It is true that you can compensate somewhat to give 'acceptable' results but an accurately exposed negative will produce an exceptional print. There is no replacement for proper exposure no matter what the medium.

-- Andy Laycock (agl@intergate.bc.ca), September 26, 1998.

This topic keeps coming up, in various forums. I agree with Andy: the correct exposure is the best exposure.

For merely "ok" results, people talk about B&W negative latitude. If you meter a grey card, you will get good detail in shadows about 2 stops below that reading, and highlights about 6 stops above. (Speaking very loosely, the film has more latitude to overexposure than underexposure.) The exact numbers depend on the film and development. On that basis, if your subject has a contrast range of 8 stops, AND you meter shadows and highlights, AND you calculate the mid-point, AND you set your camera to that reading, you will capture all the tones. Depending on your meter, you *might* get the same result by setting the meter 1 or 2 stops slower than your film's ISO, and taking an average reading.

-- Alan Gibson (gibson.al@mail.dec.com), September 28, 1998.

It seems the question is "What is correct exposure?" Now if you follow Alan's analogy that your film will show detail for 2 stops below your exposure setting and maybe 6 stops above your exposure setting but to get a good exposure read the highlight and shadow and expose for the mid-point. Lets put some numbers in and see what happens: 100 ISO film, gray card reads EV 15, 2 stops below is EV 13 and 6 stops above is EV 21, that would give an exposure of 1/125 at F/16. If we find the mid-point that would be EV 17 with an exposure of 1/125 at F/32. If only 2 stops of exposure are held on the film below our exposure setting that would equate to EV 15 and everything that lived in the EV 13 & 14 range would be lost on the negative and never make it to the print. In a less contrasty photo this approach would work, in this situation it didn't. I think to sum up what most of the "Masters" have felt since the beginning of photography, those using the zone system and those using other exposure methods is DON'T underexpose and DON'T overdevelop.

-- Jeff White (zonie@computer-concepts.com), September 28, 1998.

Jeff, thanks for pointing out that error. I was trying to give an example when people might legitimately "overexpose", but my brain was going faster than my fingers, and I left out some important words. That paragraph should have read:

On that basis, if your subject has a contrast range of 8 stops, AND you set your meter to 2 stops slower than your film's ISO, AND you meter shadows and highlights, AND you calculate the mid-point, AND you set your camera to that reading, you will capture all the tones. Depending on your meter, you *might* get the same result by setting the meter 1 or 2 stops slower than your film's ISO, and taking an average reading.

Jeff also says: "DON'T underexpose and DON'T overdevelop." I only partly agree with this. I do believe that developing for more than normal is OK, when the intention is to increase contrast. In these circumstances, the film might neeed a slighty increased EI to compensate, at the shadow end of the characteristic curve. Adams calls this "N+1", or whatever. But overdeveloping in order to underexpose is only OK if we remember that we will also increase contrast.

-- Alan Gibson (gibson.al@mail.dec.com), September 28, 1998.

I agree with what Andy and Alan are saying that you should make the best exposure that you can. The point that I am trying to make is that exposure and development are relative. In a low contrast situation I would develop more than normal and probably expose less than normal if using sheet film or it is correct for the whole roll. For a high contrast subject I would expose more than normal and develop less than normal. When I suggest overexposing as a normal course of action, I am talking 1/3, 1/2 or maybe even 1 stop. Many people in my experience would be doing well if the could expose that accurately. The idea of "don't under expose and don't over develop" was written recently by David Vestal about discussions that occurred between Ansel Adams and Ralph Steiner also in an article by Howard Bond talking about the truths he has learned in B&W up til now. The idea is that if yout negative is too thin from under exposure or too thick from over development it will be difficult to get a good print, not impossible but difficult. An exposure that makes the best negative to make the best print should be all our goals. That information may not come on the side of a box or data sheet though.

-- Jeff White (zonie@computer-concepts.com), September 28, 1998.

I agree with Jeff, and here's an anecdote about "DON'T underexpose and DON'T overdevelop". My apologies if it is drifting somewhat from the topic.

When I was even younger than I am now, I used to believe that I could increase the effective speed of my film by stewing it for a long time in developer. What I didn't fully appreciate was that the major effect was to increase contrast. This raised the density of mid-tones appreciably, and I used to judge "correct" exposure as that which reproduced a grey card as grey on the negative. For some styles of photograhy, this is not a terribly bad definition of EI (Effective Index), although it is not the standard definition. However, I now normally judge "correct" exposure (and development) to be that which gives me good detail in whatever shadows I am interested.

Incidentally, the (dubious) definition of correct EI being defined as reproducing a grey card as mid-grey on the negative seems to be adopted by some manufacturers. Watch out for phrases like "you can expose at EI 3200 if you don't care what happens to the shadows".

-- Alan Gibson (gibson.al@mail.dec.com), September 29, 1998.

I have been a proffesional photographer for 18 years. I shoot tons of B&W film and still do all my own processing by hand. i have found that your exposure depends a little on how you process. My personal findings are: tri x 120 or tri x 35mm should be shot at about 320 ISO and tmax100 120 or 35mm should be shot at an ISO of 80. These both open up the shadows a little and still gives wonderful blacks.

I am a B&W lover and I think you should try a few combinations of exposures and processing procedures until you find a gray scale and density you like.....

-- john sibold (fotojohnny@aol.com), January 03, 1999.

The 'true' answer is, as in all things photographic, find a system, by experimentation, that suits your style of photography and, gives you the results you want. The only 'rule' in photography is...there are no rules!

-- "Ted" johnson (adryanj@hotmail.com), January 06, 1999.

Above----Very true I think There in NO correct exposure also, one just cannot mathch any scene to real sight of human eye, b'cos the eye can dynamically adjust to a large spectrum of intensities. the Correct expoure as you call it I think, should be decided so as to suit the Mood of the situation you want to portray. Ansel adams zone system helps a lot for visualizing the final mood of the print

thanks shreepad

-- Shreepad Joglekar (shreepadjoglekar@usa.net), July 13, 1999.