Why would one push or pull a film?
Why would one push or pull a film? I can see three reasons:
1) To compensate for certain extreme light conditions (snow, night, etc).
2) When pushing, one can use the film in less light circumstances. So the need for a flash is circumvented.
Drawback: the film generally has a worse performance.
3) If one wants special characteristics, grain, etc. But what are these special characteristics?
Any info on point 3)?
Another reason for pulling film speed is to produce more manageable negatives in everyday circumstances, and not just the extremes of lighting conditions. Many downrate their films as a matter of course to give better shadow rendition, and then give a reduced development to control highlights. If properly done this gives a tonaly rich negative which prints easily onto "NORMAL" grade paper with a minimum of fuss.
The following link is useful, and goes into great detail about establishing your own personal optimum film speed. This is from an acknowledged master of monochrome.
People commonly conflate three things: tonality, speed adjustment and contrast control. The latter two are less closely related than many people believe, at least across what one might call a 'normal' range of film contrast (gamma) of about 0,55 to 0,70.
There's also the point of metering technique. The only way to ensure adequate shadow detail without unnecessary overexposure is to meter the shadows directly, preferably with a spot meter. Ansel Adams reputedly said that when he got a spot meter, his exposures increased by a stop.
Extra exposure seldom harms tonality, and in the eyes of most, it improves it. This is why many photographers prefer to give anything from 1/3 stop to 1 stop extra exposure. I prefer just 1/3 stop when using a spot meter, but with a through-lens meter (normally designed to give optimum exposure with slide films) I generally give 1 full stop more than the meter indicates. This is neither 'pushing' nor 'pulling', but merely giving extra exposure.
Extra exposure also reduces sharpness and increases grain size, which is obviously a bigger problem with 35mm than with larger formats.
Increasing shadow detail via increased development
Speed adjustment via extended development gives extra shadow detail at the expense of higher contrast. The point at which the increase in contrast becomes unacceptable depends on the subject and the photographer's preferences.
Contrast control is a means of fitting the subject contrast onto the printing paper and is most easily discussed via logarithms.
Let's say that a given paper requires a log exposure range of 0.90 (3 stops, 8:1) to give the full density range of which it is capable: anything outside this range will read either as paper-base white or maximum black. Allow for an enlarger flare factor of 2x (1 stop, log density 0,3) and your negative density range needs to be 1,2 (4 stops, 16:1).
This is regardless of the subject brightness range. Let's say this is 256:1, 8 stops, log range 2.4, and that (once again) your camera/lens flare factor is 2, so the projected image has a brightness range of 128:1, 7 stops, log range 2.1.
Obviously if you map this 1:1 onto the negative, its brightness range will be too long. You therefore develop for as long as you need to in order to reduce 2.1 to 1.2. Divide 2.1 into 1.2 and you get 0.57, a fairly typical negative contrast or gamma.
Slot different figures into the equations -- more or less subject brightness range, different flare factors, different paper grades -- and you get different required gammas. For example, start out with a lower subject brightness range of just 128:1 and leave all the other variables constant and you end up with a projected image brightness range of 64:1, 6 stops, log range 1.8, and the required gamma is 1.2/1.8 or 0.67.
Or leave all the other variables constant but change the flare factor to 1 (a new LF camera with very well blacked bellows and a multicoated lens can approach this) and you end up with 1.2/2.4 or 0,50.
A lot depends, obviously, on your subject matter, camera, lens, enlarger and materials, and changing development time so that your negatives print on your preferred paper is nothing to do with pushing or pulling. Because of the ingenious 'Delta X' criterion built into the ISO standard, effective film speed changes less than most people think. And because the whole system is so flexible -- an extra stop of exposure really doesn't matter much, except in terms of grain and sharpness -- a lot of people who think they are being super-precise are merely taking advantage of this simple truth. Under-exposure, on the other hand, results in a swift loss of tonality.
To sum up
Give whatever exposure you need to get the tonality you like. For most people, this means overexposing -- which is nothing to do with 'pulling'.
Give whatever development you need so that your negative (or with roll and 35mm film, the majority of your negative) will print on your preferred grade of paper. Again, this isn't 'pushing' or 'pulling'.
For what it's worth, I find that with my technique, enlargers, etc., I generally prefer about 10 per cent more development than the manufacturers recommend, in order to print on grade 2. Again, this is not pushing or pulling, merely developing to get the negatives to print the way I like.
You might also care to take a look at some of the free modules in the Photo School at www.rogerandfrances.com, such as subject brightness ranges and ISO film speeds. These are not just spur-of-the-moment answers like this one, and probably contain fewer errors. They are also illustrated.
I'm one of those many. I found that far less effort is needed to get a good print using this method. It's been around for a long, long time and it works well. I can't add anything to pushing film other than my experience with Diafine, which allows you to shoot Tri-X 400 at 1200 and great results. I don't have much occasion to do this myself, but I have done it on occasion.
that was great!
all the best,
Originally Posted by Roger Hicks
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Originally Posted by John Bragg
One could argue (rightly, in my opinion) that if you do a Zone System personal film speed test and find that say, Tri-X in HC110 has an optimal film speed (for you) of something considerably less than ISO 400, (and most people will), that it's Kodak that's pushing the film, not you pulling it.
You're setting your ISO to maximize the film's capability to record tonality. Kodak is setting it to maximize latitude (and marketability). It's not that you've discovered something that Kodak doesn't know.
Good point. I guess a lot depends on how you meter ? I only know that generous exposure works better for me. I rate Tri-X at iso 200.
Originally Posted by jstraw
I find the whole concept of pushing and pulling to be photo magazine malarkey. The idea, as Roger explains, is to get the correct exposure and development for a particular negative or roll.
Originally Posted by jstraw
Umm... No. On two counts.
First count: ISO is not a matter of opinion. It is a replicable speed system with specified density and contrast criteria. Anyone who knows what they are doing and has the right equipment can test any film and get a true ISO speed which will be very close to the manufacturer's ISO speed in the manufacturer's stated developer. This does not mean that the ISO speed is necessarily the best for you, or the best for anyone, but it is a replicable standard.
Change developers, and the ISO speed may or may not change. Typically, a speed increasing developer will give at most about 2/3 stop extra (ISO 125 > ISO 200), at the cost of coarser grain, while fine-grain developers will wipe off anything from 1/3 stop upwards (ISO 125 > ISO 100 or less). Change speed point and/or contrast, and you are no longer using ISO, which is, by definition, a standard.
The personal speed you choose may well work better for you, but it is fairly unlikely to be an ISO (International Standards Organization) speed and you really should use the term EI (Exposure Index).
It is open to any manufacturer to use a speed-increasing developer for their ISO speed, but the only manufacturer I know who does so is Foma with their 200-speed film, which is indeed ISO 200 (or close enough to it) in most speed-increasibg developers but more like ISO 125-160 in (for example) D76; exactly the same speed as Ilford FP4 Plus, nominal ISO 125.
Second count: If Kodak were manipulating film speeds to maximize latitude, they would set a LOWER ISO speed, not higher. Think about it: with ISO speeds, over-exposure carries very few penalties, while under-exposure incurs a very rapid loss of quality. Until 1959/60, B+W film speeds had a one-stop 'safety factor' built in, i.e. an ASA 32 film could be exposed at ASA 64 with little or no loss of quality given competent metering. Many photographers did exactly this, complaining that ASA speeds were far too conservative. The ASA standard (forerunner of ISO) was therefore changed. You can't please all of the people, all of the time.
A small quibble about terminology (which I'm sure Roger is aware of, but I mention just to avoid confusion)--It is my impression that ISO speed does not change no matter what you do, because ISO is a specification requiring the developer specified by the ISO (that you wouldn't likely use for pictorial photography--I believe it's in Haist's _Modern Photographic Processing_), method of agitation (as I recall, it involves a machine that rotates a tank on a specific angle at a certain speed), stop, fix, and measurement.
Film speeds in developers other than the one used for ISO testing are referred to as "EI" or "exposure index." So you might find that a film which has an ISO speed of 100 has an EI of 50 in one developer, 80 in another, and 200 in another.