B&W exposure latitude

Discussion in 'Exposure Discussion' started by mingaun, Apr 12, 2011.

  1. mingaun

    mingaun Member

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    Hello,

    I have another newbie question. Almost everyone keeps saying that B&W is quite forgiving in terms of exposure. What does that actually mean? Does it mean that if the exposure is off a little we can still push and pull it back by developing the negatives differently? Because if thats the case then in my scenario this latitude flexibility will not help me because i am trying to develop the film myself and will only follow strictly to the 'rules'. Help anyone?

    Mark
     
  2. 2F/2F

    2F/2F Member

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    There is a lot you can do to print a b/w negative that is technically flawed. With b/w negs, you have the capability to make extreme manipulations fairly easily, and without having to have a ton of technical skill or experience. That is what is meant by "latitude" when used in a general sense. It's the ability to make use of something that is not ideal by way of various manipulative tools in the darkroom.

    In b/w, there are endless options in developing and printing, unlike with other processes. As far as exposure latitude specifically, and the ability to capture a wide brightness range on the film, I think color negs are superior. But you can do so much more, and so much more easily, in b/w developing and printing than you can with color developing and printing, so it is generally seen as the "easier" medium to work with.
     
  3. Steve Smith

    Steve Smith Subscriber

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    Latitude really refers to the amount you can get an exposure 'wrong' and correct for it at the printing stage.

    Wrong is a bit of a strong word to use as there are also artistic choices but if you produce a negative which is a bit too dense, it can be printed for a bit longer or a light negative can be printed for a shorter time to compensate.

    Transparency film does not have this latitude as the processed film is the finished product.


    Steve.
     
  4. polyglot

    polyglot Member

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    Say you underexpose by a stop and don't notice; you'll lose some shadow detail. If you do notice, you can correct by pushing (extending development) and get back a decent image. It will have a little more contrast if you push but you can just print it with a lower-grade filter in the enlarger. You really only get underexposure latitude by pushing, so it's not so much latitude as a deliberate decision to use the film in a different way. Don't underexpose if you can help it; the more light the better with negatives.

    You can overexpose most B&W films by at least three stops (i.e. 8x too long!) without causing any problem except additional grain. The negatives will be very dense but that just means they need to spend a little longer in the enlarger. That over-exposure latitude is what most people are referring to and it means you can select a conservative exposure setting and basically ignore the light levels until they change dramatically. If suddenly you end up with 2 stops more light, the image will still be completely fine for most purposes except the most exacting.

    Slide film with a 2 stop over- or under-exposure will come out nearly clear or nearly black; it'll be useless in comparison to what you can do with a B&W shot.

    Modern C-41 (colour neg) has as much overexposure latitude as B&W but it's more difficult to recover from because the saturation generally reduces with overexposure and some colours can go wonky, which is hard to correct for using only analogue techniques.
     
  5. ic-racer

    ic-racer Member

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    1) Film speed and development are independent
    2) ISO exposure is the minimum exposure needed for a quality print under controlled conditions.
    3) There is no ISO standard for the maximum exposure tolerable to make a quality print...therefore
    4) There is no ISO standard measure of film latitude
    5) Most all contemporary B&W films will exceed the range of the common 21 step wedge...therefore
    6) It is somewhat difficult to have a meaningful discussion of B&W film latitude
     
  6. mingaun

    mingaun Member

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    Thank you all so much. Now i feel much better. I guess in a nutshell, i should err on the side of overexposure rather than underexposure. At least then i know that i have the raw data that if anything could be 'corrected' at the printing stage. This is wonderful.

    Another side question is, digital black and white obviously does not have this latitude right? I used to take color shots in my D200 RAW and convert it to B&W. Is it correct to say that the dynamic range for digital is not as many stops as the film's B&W? If thats the case then would it be right to say that in this one area film is definitely better than digital??

    Mark
     
  7. RalphLambrecht

    RalphLambrecht Subscriber

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    Correct, when in doubt overexpose and underdevelop! B&W film has a huge latitude towards overexposure (10 stops and more) and almost none towards underexposure (see ice-racer's comments).

    Yes, digital is currently limited to an overall dynamic range of 9 to maybe 11 stops, but we don't discuss digital on APUG.
     
  8. polyglot

    polyglot Member

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    While B&W negative has overexposure and very little underexposure latitude, digital is the opposite. You can correct nearly any underexposure on digital but no overexposure.
     
  9. RalphLambrecht

    RalphLambrecht Subscriber

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    True, in this regard, digital is similar to slide film.
     
  10. dfoo

    dfoo Member

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    If you underexpose with digital you end up with noise (or nothing) in the shadows. Shooting B&W film is much easier... make sure you have sufficient exposure and you'll end up with something printable.
     
  11. Saganich

    Saganich Subscriber

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    I was shooting at a friends wedding and my shutter speed dial malfunctioned causing a 4 stop overexposure using TriX. The dresses were just white blobs. For fun I mixed up a proportional reducer and brought each roll to a normal development. I was impressed how well it worked. It is much harder to add density to negatives.
     
  12. keithwms

    keithwms Member

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    B&W print/negative film handles overexposure very well. That's the key point to understand, for someone new to this.

    The best overall dynamic range I have found in the (high end) digital world is about 12 stops. When you compare that to old panatomic x film developed in POTA... well there is no comparison. That combination has been shown to provide up to 20 stops of range!!! If I remember correctly, POTA was developed for blast imaging.

    But there is of course a lot more to this than dynamic range alone. What you will hear/read film photographers discussing is the toe and the knee of the tone curve (of film and also of photopaper). That tone curve provides a very different look, that many would say is more pleasing than the rather linear response you get from raw digital. In a nutshell, the tones ease into the highlights and the shadows quite gently- not abruptly and with posterization. Digital users must curve their linear scale to get that pleasing look; with film, it's built in. And every film has a different and characteristic 'look' with respect to knee and toe.

    But the main point is how b&w print (neg) film handles overexposure. You can record lots of highlight detail.

    P.S. I have an illustrative example from a few years ago that taught me a lot about this issue. I made a big mistake when shooting something on vacation. I had set up an infrared shot, using a deep infrared filter, and the (#87) filter cutoff was so deep that I needed a filter factor of many stops, 8 or 9 or so stops, as I recall. In other words, I timed the exposure to be 8-9 stops longer than sunny 16. And this was in high noon desert light, near Sedona, Arizona... virtually no clouds!

    Problem was... in my haste to get the shot, I forgot to put on the bloody IR filter when I actually took the shot! So I overexposed by a ridiculous amount. I got my negs back from the lab and they were black to the eye. I mean it: black. Then I held one neg up to a lightbulb and could barely make out a wee bit of detail, so I thought, okay, why not scan it and see if there's anything there before I bleach the hell out of it and try to get something. So scan it I did. And voila... here's what a ~8-9 stop overexposed b&w film shot looks like... actually not half bad! Not pretty but.. hey it's an image.

    http://s25.photobucket.com/albums/c76/keithwms/?action=view&current=tree-yuck-cr.jpg
     
  13. mingaun

    mingaun Member

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    Thank you all for your helpful comments.

    Keith in your example of severe overexposure, you said your negatives was almost black. In normal circumstances to salvage this you need to do some special printing procedures isn't it? But if you just scan it on the computer I presume it would be almost black with almost zero detail right? My understanding is that the latitude advantage of black and white film is manipulated in the traditional developing and printing process but not in the scanner procedure.
     
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  15. Sirius Glass

    Sirius Glass Subscriber

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    I took a photograph of Half Dome in Yosemite National Park just after a snow storm. Before I took the photograph, I checked the light readings with a spot meter and found that the Subject Brightness Range [SBR] was 12 f/stops. I used Kodak Tri-X at box speed and developed normally in XTOL replenished. The film easily captured the full range without blowing out the highlights and catching details in the darkest parts. The tones of the clouds were different than the tones of the snow on the top of Half Dome. I have been told that film can handle 14 f/stops and I could see film covering 20 f/stops.

    Steve
     
  16. keithwms

    keithwms Member

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    The latitude of b&w neg film is helpful in both workflows.

    In the traditional workflow, you just "print through" the thick neg, i.e. you do a longer exposure to the paper. You will also need to do a contrast adjustment, e.g. print to multigrade paper and fiddle with contrast and perhaps do split grade printing. This is because all the info you want is bunched up in a narrow range of optical densities.

    In the scan workflow, the optical density of the thickest (=most overexposed) negative is well within what most scanners can handle. A good flatbed can manage close to DMax 4 - about as dense as Velvia can get. Even a wildly overexposed b&w neg reaches nowhere near that optical density. So what happens is you scan the neg and find that the tones are all bunched up, but then you 'auto-level' the tones to try and get the right contrast. It is very easy. Actually easier than traditional route, I daresay... but not necessarily better :wink: Anyway that is a topic for DPUG.

    So... either way, the latitude of film real shines.

    There are, of course, consequences of overexposure. But the point is that you can overexpose a neg film quite severely and still get a usable image. And even if you don't overexpose wholesale, another point is that little specular highlights will be held in detail, e.g. highlights on jewelry or a wedding dress, chrome on a car, reflections on water, etc...
     
  17. polyglot

    polyglot Member

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    When shots are overexposed like Keith's (I've done the same thing with IR820 and leaving the filter off, I seem to do it once every couple of rolls), you just need to use a longer exposure in the enlarger. The very dense negative lets the light through slowly, so it just takes longer for an image to form on the paper. Same principle in scanning - a film scanner has an exposure control which controls how long the scanner's CCD is exposed to the negative. Dense negatives just need more exposure.

    As you can see, it's become very grainy and of poor contrast, particularly in the highlights, but you can tell what is there. If you did that much overexposure (even 4 stops = 16x, not even the 8 stops = 256x here) with digital or slide film, you would have a perfect white field from which absolutely nothing was recoverable.
     
  18. mingaun

    mingaun Member

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    Thank you all for your helpful information. Things are getting much clearer now to me. Also now i realise how important a spot meter is for black and white. I can at lest ensure the darkest scene with detail will be exposed correctly. Too bad there is no small spot meter in the market.

    Mark
     
  19. MattKing

    MattKing Subscriber

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    Mark:
    With respect, you are over-thinking this. You won't see most of the benefit from a spot meter until you are a lot more experienced with film and your camera. As a beginner, I would strongly suggest that you concentrate first on getting the correct exposure for mid-tones and highlights, because they will have the biggest influence on how your photographs look. Incident meters or averaging reflected light meters are fine for that purpose.
     
  20. BetterSense

    BetterSense Member

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    Last summer I had my Canonet set for indoor conditions at f/1.7 and 1/60th of a second. I accidentally left it on that setting and took a picture of a fish I caught outdoors during the day. By my calculations that's at least 8 stops of overexposure. I figured it was a lost cause but when I attempted to print it, I did get a picture that was recognizably a fish... I wouldn't recommend it unless you know what you are asking for; the picture was pretty grainy with cooked highlights but honestly a lay person would probably think it was fine.
     
  21. RalphLambrecht

    RalphLambrecht Subscriber

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    Here is a little bit more info on B&W negative film latitude, demonstrating the film's insensitivity to overexposure as well as its sensitivity to underexposure.
     

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  22. Steve Smith

    Steve Smith Subscriber

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    Ralph's second graph shows in a clear and easily understood way, something which I have been trying to put into words. I don't need to bother now!


    Steve.
     
  23. ic-racer

    ic-racer Member

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    The only thing I would think different is that the negative is not "overexposed" until it the high values start to fall off the shoulder and print quality has degraded. So, the dark gray box in the second diagram (nice diagrams by the way) I'd say "more than needed, but still OK exposure" rather than "overexposed."

    In fact in large format photography (where high shutter speed is not needed), dense negatives show less dust when printing and in my hands, are preferred.
     
  24. RalphLambrecht

    RalphLambrecht Subscriber

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    ic-racer

    Some people have an issue with the term 'overexposure', and I can understand why, because overexposed negatives print just fine and often better than normally exposed negatives. If we free ourselves from connecting 'overexposure' with 'bad exposure', the term gets is to digest. 'More exposure than needed, but still OK exposure' it a bit too lengthy for something we do so frequently. I prefer to stick to 'underexposure', 'normal or minimum exposure', 'overexposure' and maybe 'nuked'.
    :D
     
  25. mingaun

    mingaun Member

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    Ralph, thanks for those images which speaks very clearly.

    Mark
     
  26. fralexis

    fralexis Member

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    So it IS a good practice to shoot at one half the rated ISO? I'm also struggling at getting consistently good exposures. With my spot meter, I find it hard to determine what is middle grey in a landscape. I want to try just placing a dark shadow in zone III. Otherwise, I'll use my digital meter :smile: