Exposure and contrast: the big confusion.

Discussion in 'B&W: Film, Paper, Chemistry' started by daniele_vittorio, Jul 16, 2012.

  1. daniele_vittorio

    daniele_vittorio Member

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    Hi out there,

    sometimes my negatives turn out a bit flat, and i would like to get more contrast.

    Now here comes the confusion:

    Some people advise me to OVER-expose the film and then develop it regularly.

    Other people say, more contrast is reached by UNDER-exposing the film and then push-processing it.

    So where does the truth lie?! Or is both correct?
     
  2. Prof_Pixel

    Prof_Pixel Member

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    It all depends....

    With your B&W film, if you are underexposed you will be in the low contrast toe of the Characteristic Curve; giving more exposure will move you to the higher contrast portion of the curve.

    If you are already correctly exposed, you will need to underexpose slightly and push-process it.
     
  3. haryanto

    haryanto Member

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    there's rule in zone system, exposed for shadow develop for highlight, so you can control your overal contrast, u place shadow in zone III or IV then you give more time indevelop to rise the highlight
     
  4. Doremus Scudder

    Doremus Scudder Member

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    Ciao Daniele,

    Neither is exactly correct. Remember the age-old adage: Expose for the shadows, develop for the highlights.

    One could reformulate it like this: Expose for the shadow detail you want, develop for the contrast you want.

    The problem is, it is often hard to tell the difference between an underexposed negative and an underdeveloped one; both will have less contrast than ideal to make a pleasing print.

    Here are some guidelines:

    If your negatives are flat, but you have adequate detail in the shadows, you need to develop longer. (underdeveloped neg.)

    If you have bad shadow detail and less contrast than you want, you may get where you need by simply exposing more. (underexposed, but correctly developed neg.)

    If you have less shadow detail than you want, but whites and blacks in the print, you should expose more and develop a bit less. (underexposed and overdeveloped neg. Note: this is what happens with traditional "push processing")


    Also, keep in mind that different scenes require different contrast controls. If you print on paper, then much of your contrast control will come from changing paper grades. Unless you shoot sheet film and use the Zone System or one of the other methods that determines development for each negative individually, you will want to aim for your most common situation and middle ground, and use the contrast controls of paper grade change to deal with unusual situations.


    Hope this helps some,

    Doremus

    www.DoremusScudder.com
     
  5. Gerald C Koch

    Gerald C Koch Member

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    Exposure does not determine contrast but rather density. Development determines contrast. If your negatives are consistly flat then decrease your exposure and increase your development time. Try changing each by 15% to start.

    Read a book like Ansel Adams' The Negative rather than asking people.
     
    Last edited by a moderator: Jul 16, 2012
  6. tkamiya

    tkamiya Member

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    If you are using your film correctly and developing correctly, your images should not be flat. It should be about right. It should print OK with grade 2 or 3 filter. If this is not the case, something is wrong. Before using various techniques to enhance your contrast, you should investigate where and what is going wrong and correct it.

    First place to check is, if you are exposing it correctly. You can kind of sort of tell this by looking at your negative. Is it overly thin or overly dense? Second place to check is, is it being developed correctly. Are you able to develop it at specified time at specified temperature? Are you agitating it correctly?

    Can you tell us how you are judging contrast?
    Can you tell us what your negative look like?
     
  7. smieglitz

    smieglitz Subscriber

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    A verbose restatement of some things previously shared:

    A normal image with a fixed subject brightness range depicts a set of objects in print tones from black to white = normal contrast.

    If you overexpose, the stuff that is supposed to be black on the print is now dark gray and the same objects in the shot now go from dark gray to white (where some of what should be light gray tones are now blocked up but may still be printed by burning in) = loss of contrast.

    If you underexpose, the stuff that is supposed to be white on the print is now light gray and the same objects in the shot now go from light gray to black (where some of what should be darker gray tones are now gone forever beneath the exposure threshold) = loss of contrast. This is why you should expose properly for the shadows. If the shadow exposure falls below the threshold, you can't print what is no longer there.

    If you underdevelop, the stuff that is supposed to be white on the print is now light gray (or darker) and all the other grays (except the black stuff) are darker than they should be and the same objects in the shot now go from black to light (or darker) gray = loss of contrast.

    If you overdevelop, the stuff that is supposed to be black on the print becomes just slightly lighter and the lighter grays have become lighter or white because development affects the areas that have received more exposure on the negative to a greater degree that those areas receiving less exposure. That's why you develop for the highlights. Increased development doesn't change the shadow tones very much but has a great effect on the midtones and highlights. So, with overdevelopment the same objects in the shot can now go from almost black to white = loss of contrast, but not as much as with the other three variables.

    You will get an increase in contrast from the set subject brightness range only with overdevelopment. If the subject tones only go from black to light gray, and there is nothing truly white, overdevelopment can increase the density of those areas in the negative to make them print as white = increase in contrast. The shadows will get a bit lighter, but not much. If you just very slightly decrease the exposure to compensate (by shooting at an ISO 1/3 stop lower for example) and then overdevelop, you'll end up with pretty much everything still recorded on the negative but with an increase in contrast.

    The combination of intentionally underexposing slightly and then overdeveloping to raise the contrast is known as "pushing" (or "expansion" in Zone System lingo). "Pulling" or ("contraction") is the opposite condition. (OE + UD)

    Pulling (contraction) and pushing (expansion) are intentional, and tools that can be used to tailor contrast and tonal range in the negative and print.

    Underexposure, overexposure, underdevelopment, and overdevelopment when not intentional are simply mistakes and to be avoided.
     
  8. Pioneer

    Pioneer Subscriber

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    Art of Photography

    Go find a copy of the "Art of Photography." I am still learning and am already on my 3rd read through that book, particularly the exposure and developing chapters, but it has already helped my understanding immensely.
     
  9. markbarendt

    markbarendt Subscriber

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    +1
     
  10. LJH

    LJH Member

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    If you're putting he shadows in Zone IV, wouldn't you need to give less development time to control the (now) overexposed highlights' density?
     
  11. johnielvis

    johnielvis Member

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    you can get high contrast prints with flat negatives---use the higher grade filters or a higher paper grade

    for real contrast you want to push the hell out of the film--then when you print you'll only be printing black and white with no shades of grey inbetween, since there won't be any

    for reversal black and white you get lower contrast by overexposing and higher contrast by pushing

    you can also try to use intensifier on the film or bleach if you "overdevelop"...that's the best maybe ---overdevelop and then bleach by inspection...try print...if too little contrast, the bleach the neg more and have another go....this is how you can gradually increase the contrast
     
  12. Bill Burk

    Bill Burk Subscriber

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    LJH,

    When you place shadows in Zone IV, you print them down to Zone II. The highlights, for example if they fell on Zone XI, should follow down to Zone IX on the print.

    daniele_vittorio,

    Hope you got answers you can use...

    If you can't see detail in the shadow of the negative then I recommend exposing more, whether you plan to develop longer or not.

    If you get detail on the neg, you can always use higher contrast paper to get more contrast when you print.

    If you still think the negatives are flat you can develop the film longer. You can tell the lab to push the film if you aren't developing it yourself.

    I'd recommend making one change at a time.
     
  13. Gerald C Koch

    Gerald C Koch Member

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    I don't think that the OP is at the stage where any discussion of the Zone System is going to be anything but incomprehensible to him. So mentioning it is really not helpful. Then too it is only practical for LF photography and not 35mm which he shoots.
     
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  15. Bill Burk

    Bill Burk Subscriber

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    daniele vittorio,

    Gerald's right, Zones are not what you want to be thinking...

    Tell the lab to push one more stop than you really shot.

    If you shoot at twice the film's rated speed, tell the lab to push your film 2 stops.
     
  16. c6h6o3

    c6h6o3 Member

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    How do you know they're flat? Have you printed them?

    A little story: I once sent a slightly underexposed and very underdeveloped (and I mean wafer thin) negative to Michael A. Smith. I never bothered to print it, thin as it was. Either he or Paula printed it and sent me back 4 stunning prints from it made on grade 3 paper. That was a real eye opener. Since I often use staining developers, many negatives really surprise me with how much contrast they convey to the print. I never pre-judge any more. I always make the best print I can from a negative before I judge it.

    In any case I would start with pinning down the shadow density first, then worrying about the contrast. Shoot a roll of an average scene during the day at box speed (maybe put a gray card in the scene to meter on), and expose -1,-2,-3,0,+1,+2,+3. Develop according to the directions with the developer and then print them all. Make the best print you can of each negative. The one with shadow detail the way you want it tells you what your film speed should be. In my case I expose HP5+ roll film at 100. (Box speed is 400.) I use an incident meter for a handheld roll film camera. In my view camera I expose sheet film at 200 speed, but I place the shadows on Zone IV. So Zone System purists who put their shadows on Zone III would say that I'm really exposing the film at 100. Whatever, I get negatives that print the way I want them to. Similar trial and error with development yields contrast the way I want it.

    It's all about how you want your pictures to look. Just never forget that you're making negatives to print. Always ask yourself "How will this negative print?" There's only one way to get the answer.
     
  17. LJH

    LJH Member

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    I'm pretty sure that the highlights at XI will be blocked up if you don't reduce the Dev time, let alone add to it as haryanto suggested.
     
  18. Leigh B

    Leigh B Member

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    Exposure controls shadow detail. If underexposed, there is none.

    Development controls highlight density. More development = greater highlight density without changing shadow density significantly.

    - Leigh
     
  19. Bill Burk

    Bill Burk Subscriber

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    I don't want to risk confusing the original poster by continuing Zone System terms in this thread, and I want to reasonably simplify. This applies "within reason" as long as you don't start with a high contrast scene.

    Contrast is basically the difference between dark and light. Overexposing won't increase the contrast, it bumps up the shadows and highlights equally. Yes the highlights go where you might worry about them. But you print longer because shadows are overexposed just as much, so highlights come back down.

    Pushing (developing longer) bumps up contrast. Then the difference between dark and light spreads. Then you have to be careful not to block highlights.
     
  20. dehk

    dehk Member

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    With a flat neg you can print it in high contrast while the neg actually still has all the details if you change your mind. Like some suggested, how do you know they are flat?
     
  21. ooze

    ooze Member

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    As far as I know, this is not the complete picture. Development does indeed change the contrast curve with more development raising the curve. However, if you have already developed your negative then you're stuck with whatever curve you get and your exposure further determines the contrast characteristics of your negative. You could have exposed your negative such that all density values fall on the straight line of the curve, but it's also possible that you've exposed too little and the dark tones are on the toe of the curve, resulting in lower shadow contrast and also lower overall contrast (difference between lowest and highest density values).
     
  22. David Allen

    David Allen Member

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    The concepts of the Zone System are not hard to grasp and the associated testing is simply a way of eliminating the variables that the OP is currently confronted with. Also, I have never understood why people believe that the Zone System is only practical for large format users.

    The simple answer to the OP's question is that, in practice, exposure controls the amount of shadow detail and development controls the contrast:

    If you have flat negatives with detail in the shadows then you are not processing for long enough (increase by 20% in the first instance).

    If you have flat negatives with too little detail in the shadows then you need to give more exposure and develop for longer.

    If you pin down your exposure technique and processing then you can get on with the real business of enjoying your photography. For details of how to do this, you can read my detailed instructions in this thread:

    http://www.apug.org/forums/archive/index.php/t-106488.html

    Best,

    David
    www.dsallen.de
     
  23. pdeeh

    pdeeh Member

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    it is not hard to grasp for those people who do not find it hard to grasp ... others find it extremely difficult to conceptualise, however much we read, and could easily become a stumbling block if we feel that we cannot progress without understanding something which we may be unequipped to understand.

    threads like this are useful "seminars" for others like the OP (me for instance) who are starting out, and much can be learned
    from them.

    However, I suspect that for some people (I'm thinking of myself of course) the Zone System may be learned as a later refinement of technique, rather than as a foundation step.

    Keeping things (explanations, suggestions) simple are key to helping those new to home developing and printing ...
     
  24. Michael R 1974

    Michael R 1974 Subscriber

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  25. Diapositivo

    Diapositivo Member

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    I am not a printer myself, but I understand that because the Zone System asks that for every frame a decision is made regarding exposure and development time in order to compress or expand contrast so that the final picture corresponds to the image visualized by the photographer, this makes it impractical with small format and medium format because you cannot develop each frame differently and so the ZS proper cannot work unless you carry 5 cameras with you so that in each camera you have frames that will have to be developed the same way for the same effect.

    If one uses variable contrast paper, or different papers of different contrast, then this is not any more the Zone System strictly speaking. As far as I gather at the time of Ansel Adams the contrast of the paper was basically fixed, so his problem was to expand or contract contrast while manoeuvring only on the negative lever. That requires fiddling with a different development for each frame.

    I side with those saying that talking about the ZS is overkill here. I think the OP should rather give details about film - developer - development time - development temperature and his exposure technique. Maybe there is an obvious mistake somewhere in his workflow.
     
  26. markbarendt

    markbarendt Subscriber

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    Actually Fabrizio, I'll suggest that you actually use the some of the zone system's basic principles yourself.

    Spot metering, unless you always use a mid-tone as your target, requires applying an offset to find camera exposure.

    Finding exposure by measuring highlights or shadows or faces or whatever is essentially zone system work.

    Adams himself even taught the use of zone system principles for roll film shooters.