Why would one push or pull a film?

Discussion in 'B&W: Film, Paper, Chemistry' started by michielp, Sep 15, 2006.

  1. michielp

    michielp Member

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    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)?
     
  2. John Bragg

    John Bragg Member

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    Hi Michiel.

    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.

    Regards, John.

    http://www.barrythornton.com/
     
  3. Roger Hicks

    Roger Hicks Member

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    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.

    Tonality

    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

    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.

    Cheers,

    Roger
     
  4. reellis67

    reellis67 Subscriber

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    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.

    - Randy
     
  5. jnanian

    jnanian Advertiser Advertiser

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    thanks roger,
    that was great!

    all the best,
    john


     
  6. jstraw

    jstraw Member

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    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.
     
  7. John Bragg

    John Bragg Member

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    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.

    Regards, John.
     
  8. juan

    juan Subscriber

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    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.
    juan
     
  9. Roger Hicks

    Roger Hicks Member

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    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.

    Cheers,

    Roger
     
  10. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    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.
     
  11. jstraw

    jstraw Member

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    Good points. I should have stuck with a term like "personal film speed" and not ISO.

    My point about marketing is that a faster film has marketability that slower films lack. Or, I should say had. There's basically no such thing as a consumer market for B&W film anymore...or film at all for that matter.
     
  12. fhovie

    fhovie Subscriber

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    Really good and complete replies that all reflect what I have observed and practice - maybe for me it is a little less complicated:

    For large format, the issue is rarely speed, It is always to get the Scene Brightness Range (SBR) to make a negative with a Density Range (DR) to work with a particular paper (Grade 2). The DR needs to be 1.25 on my densitometer on the Ortho setting.

    If the SBR is 5 stops using a spot meter from detail shadow to detail highlight, I will likely push the film - normal development would give me a DR of 1.0 (Grade 3) (FP4+ selected - contrastier and better for pushing - and calibrated for a 5 stop range SBR - very common)

    If the SBR is 9 stops, I will use TRI X and develop it normal - TRI-X can suck up 12 stops or more if pulled.

    My processes including rating film speed, film choice, developer choice and developing time, are all calibrated for negative density ranges that are a good fit with the paper, enlarger style (condenser) and - Forte FB paper and the PC-TEA developer I use.

    For roll film, there are other considerations. I will likely not be using a tripod (If I can set up a tripod, I can use LF) so to me, roll film means hand held. Most of my hand held subjects are live and in less than contrasty light. Speed and greater contrast are both desired. I use TRI-X at 1600 developed in MYTOL (XTOL) which gives me very smooth grain (Easily enlarges 6x6cm to 16x20) and good sharpness. I also get an N+2 bunp in contrast which helps with the 3 to 5 stop typical SBR. I also shoot a lot of Delta 3200 (at 3200) and develop it in Microphen with very good results. I do not get the contrast push with the Delta and the base fog can be as much as .4. I do get some very good results overall with it though for all indoor low light shooting. Flash photography is a whole nuther thang - That gets back to tripods, slower film (FP4) and set up time etc. I like natural light for candid shots. My best results are from TRI-X but I never hesitate to keep the other film back handy with Delta 3200.

    If I do shoot handheld outside, I use TRI-X and develop in P'cat-P at ASA200 which will likley give me the DR I need. If the roll has a wide range of exposures on it from SBR of 3 to 9 all on one roll, I often use split D23. It is a compensating developer that will back off on the high contrast scenes and will work longer on the low contrast scenes, giving me very printable images thoughout the range. The cost is a little sharpness loss compared with the normal high accutance developers I use.
     
    Last edited by a moderator: Sep 15, 2006
  13. Roger Hicks

    Roger Hicks Member

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    Dear David,

    That used to be the case, but a friend who was until recently on the ISO committe assures me that the standard now allows the manufacturer to use any developer, provided he specifies what it is, hence my observation that ISO speeds do in fact change with the developer. This was precisely because, as you pointed out, the old ISO developer was far from ideal, as it flattered some films and showed others in a less favourable light.

    On the subject of agitation, I am not sure, but as far as I am aware the only requirements are the speed point of 0,10 above fb+f and the rather strange-seeming contrast criteria which, as Steve Benskin's brilliant paper on the Delta X criterion argues, effectively re-create the old Kodak fractional gradient criterion. Increased agitation (implying a higher toe speed) is, as far as I am aware, now permissible too. I could be wrong on this but I am pretty confident about the developer. I do not recall how long the rules have been changed but it is a few years now.

    Cheers,

    Roger
     
  14. Roger Hicks

    Roger Hicks Member

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    Absolutely true -- which is, of course, why ISO was so welcome, being based on the ISO standard which in turn was a Kodak standard in about 1940. This was far better than the old days when the marketing department had more to do with film speed than the sensitometry department.

    I apologize, incidentally, if I came across as unnecessarily pedantic and schoolmasterish in my last post.

    Cheers,

    Roger
     
  15. gainer

    gainer Subscriber

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    I do a lot of pushing and pulling, but I do it in the enlarger. Sometimes I push my film through the negative carrier, and other times I pull it.
    [I hope I don't get fired for that.]
     
  16. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Thanks, Roger, for your reply. You are probably more up to date on the ISO spec than I am, though I would still call any kind of individually tested speed an EI.

    The real issue for the original poster, of course, is what gets the desired result, and the "box speed" is always only a guideline or a starting point.
     
  17. Roger Hicks

    Roger Hicks Member

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    Dear David,

    I would not argue for a moment with your latter observation, and the only quibble I would have with the former is that there are one or two individuals -- I am certainly not among them, and I take it you are not either -- who do have the capacity to do actual ISO testing; Geoffrey Crawley, for example.

    The only claim I would dare make for 'ISO' testing on my part is that if one of my film curves precisely matches another -- as, for example, my curves for Ilford FP4 Plus and Paterson Acupan 200/Fomapan 200 did -- then I can fairly say that the ISO speed is the same, even if I cannot say exactly what it was.

    The vast majority of my ISO information comes from Ilford, and specifically from Mike Gristwood, late of Ilford and also late of the ISO standards committee. Ilford tested ISO speeds in various developers and -- most importantly -- habitually give different EIs, not ISO speeds, for their different films in different developers.

    This is perhaps the most important part. It means that while the true ISO speed for (let us say) Pan F in Perceptol, ID-11 and Microphen may vary from about 32-40 to a good 80, the development times are all given for EI 50 and will therefore relate to slight overdevelopment (in Perceptol) to slight underdevelopment (in Microphen). All three will give a usable EI 50 with a nominal ISO 50 film -- thereby elegantly demonstrating your points about the difference between EI and ISO and the way in which ISO is a starting point.

    Cheers,

    Roger
     
  18. Bob Carnie

    Bob Carnie Subscriber

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    I push process all my film that is slated for lith printing and solarization. the added contrast in the negative is good for both these processes.
     
  19. JBrunner

    JBrunner Moderator Staff Member Moderator

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    I generally over expose, but develop normal. Not really a push, but it gets me the negatives that print well for my particular idiom. I concur with the personal film speed concept.
     
  20. Roger Hicks

    Roger Hicks Member

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    Indeed, the ill-informed would regard that as a 'pull', and not a push or (as you so correctly say) 'normal'.

    Cheers,

    R.
     
  21. JBrunner

    JBrunner Moderator Staff Member Moderator

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    I should have written "push or pull" as the terms refer to over or under development based on under or over exposure, respectivly.
     
  22. Roger Hicks

    Roger Hicks Member

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    Sorry, I didn't mean to imply otherwise; my intention was simply to agree with your separation of exposure and development.

    Cheers,

    R.
     
  23. JBrunner

    JBrunner Moderator Staff Member Moderator

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    I just felt that in retrospect, I was not clear in my statement. No implication on your part was meant to be inferred. :smile: