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Thread: Exposing at non-box ISOs: Why?

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  1. #1

    Join Date
    Mar 2017

    Exposing at non-box ISOs: Why?

    I'm doing my best to get started in LF B&W, and have nearly completed acquiring what I need to get started. I plan to develop my own 5x7 film, and -- for now -- scan the images. Later, I'd like to try contact printing. I see myself doing landscape almost exclusively, and am planning a trip to the western US later this summer (Grand Tetons, Yellowstone, Glacier, Rainier, Crater Lake, Oregon coast, Redwoods; all are possible).

    I've decided that FP4 is the film I want (again, for now), and I've read a fair amount about it and other B&W films. One thing I've come across is lots of folks saying they shoot it at ISO 80, or 64. Others say to shoot it at box speed.

    I have two questions:

    1. What is the reason to expose the film to more light than the maker recommends? Just what will this do, and why would you want to do it?

    2. If one does expose at a different ISO, should one then develop the film based on that ISO, or develop for the box speed?

    I know that experienced folks might respond, 'just get out there and see for yourself', and I do intend to do that, but I like to understand the why of things, and besides, I'm likely to screw up my first attempts, so would like to know what the images are supposed to look like!

    If this topic has already been discussed ad nauseum, a link to one of those discussions would be appreciated. I will say, though, that one reason I'm making my own post about it is that, as a less-than-even-a-novice, I've already read some discussion of it, and found much of it contradictory, or at least unclear. I realize that so much of photography is subjective, but the subjectivity is based on something real, and I'd like to understand that reality when it comes to this topic.

    Some of the confusion on my part comes from what seems to be a clash between those who swear by the Zone system, and those who do not. While I don't want to start a debate on that, I am wondering if this use of more exposure has to do with that debate. Or am I off on that?


  2. #2

    Join Date
    Sep 1998
    Oregon now (formerly Austria)

    Re: Exposing at non-box ISOs: Why?

    Hi Paul,

    I'll take a shot at answering your questions.

    People rate film speed differently than ISO for several reasons, usually related to their meter, metering technique, developer, developing technique or equipment variances.

    Zone System users employ a metering system that is based on a speed point that is slightly different than "box speed." Usually it lies about 2/3-stop slower than box speed. My Zone System testing usually always yields an E.I. (exposure index) that is 1/3-stop slower than box speed.

    Metering technique or the meter itself can make a difference, as do the type of scenes you choose to photograph and the feeling you want in a print. Often, people get better results (usually more satisfying shadow detail) by rating the film slower than box speed.

    The choice of developer and the contrast gradient one develops to also makes a difference. Some developers just don't yield box speed (e.g., Kodak gives different E.I.s for its films in different developers). Those who use condenser enlargers often develop to a lower contrast gradient than those using diffuse light sources. This can slow down the film a bit.

    Black-and-white film is very, very forgiving of overexposure, but shadow detail disappears quickly with even slight underexposure. Many rate their film slower than box speed simply as a safety measure. With 5x7 film, grain from a bit of overexposure is a non-problem, but loss of shadow detail due to underexposure is an ever-present danger. Have half or two-thirds of a stop safety margin is not a bad idea.

    More on metering: Those who use averaging metering or simple incident metering aren't directly measuring the shadows. In many situations, especially contrasty or high-key situations, an average or incident reading will give an exposure that underexposes the shadows. We are supposed to recognize those situations and give exposure compensation, but many don't and not all situations are that easy to assess. So, a safety margin is a good thing.

    FWIW, I have great prints from negatives overexposed by two stops or more. The information is all there; one just has to print through the extra density. For scanning, you'll want to try to avoid gross overexposure, but a stop over will simply not make a noticeable difference.

    Now to your second question, which is based on a misconception. There is no different development required that is directly related to a change in E.I. Development time has to do with contrast gradient, i.e., how much difference there is between tones of given exposures on the film. Many simply think of this "negative contrast" and are aware that more development = more contrast (more difference between tones) and less development = less contrast. Ideally, the development time should be tailored to the brightness range in the subject; low-contrast scenes get more development, high contrast scenes, less. This is exactly what systems like the Zone System or BTZS are based on.

    However, with today's post-processing contrast controls (paper contrast or PS), many just standardize on one development for "average" scenes and use the controls to deal with things than require more or less contrast. This, in essence, is what the manufacturers' recommended development times are based on: the film is developed to a contrast gradient that works for the vast majority of scenes given the changes you can make printing or image processing.

    Confusion enters when we talk of "pushing" or "pulling" film. Pushing is basically intentionally underexposing the film with the awareness that shadow detail will be lost (sometimes that is the goal, sometimes it's a necessary compromise for a low-light situation). The resulting negatives will have no deep shadow detail, mid-tones low on the scale and highlights exposed somewhere in the mid-tone range of the negative exposure scale. To achieve more contrast on the negative in order to make better prints, more tonal separation (contrast) is required. Hence, more development is required to get the highlights up to the negative density they should have. That's why you see things like, "two-stop push development time," etc. Pulling is the opposite: overexposing and underdeveloping. This is used much less than pushing, and usually to tame high-contrast situations or materials. For example, many FP4 users find the film contrasty, and give more exposure and less development than recommended in order to get less contrast overall.

    If you're just starting out, my recommendation would be to rate your film a bit slower than box speed just for safety's sake (5x7 film ain't cheap) and develop using a developer and time recommended by the manufacturer. Things like the Massive Development Chart and other second-party recommendations are notoriously inaccurate and highly-individual. They serve as a starting point only.

    Perhaps the best advice is still Kodak's: If your negatives are consistently too thin (underexposed), then give more exposure (rate the film slower). If your negatives are consistently too contrasty (overdeveloped), then reduce development time. And, of course, vice-versa for both of the above. Some good field notes and a bit of experience and you'll consistently be producing printable negs in no time.

    Hope this helps,


  3. #3

    Join Date
    Sep 2003
    Massachusetts USA

    Re: Exposing at non-box ISOs: Why?

    Quote Originally Posted by Doremus Scudder View Post
    I'll take a shot at answering your questions.
    Superbly done

  4. #4

    Join Date
    Feb 2012
    Yorkshire, England

    Re: Exposing at non-box ISOs: Why?

    I am starting to get impressed by the amount of time that some established members invest in answering question such as this.
    You are a credit to the forum, DS, and much appreciated by novices such as me.


  5. #5

    Join Date
    Sep 2012
    Mt. Pleasant, Wisconsin USA

    Re: Exposing at non-box ISOs: Why?

    +1 re the discussion offered by Doremus!
    ... JMOwens (Mt. Pleasant, Wisc. USA)

    "If people only knew how hard I work to gain my mastery, it wouldn't seem so wonderful at all." ...Michelangelo

  6. #6

    Join Date
    May 2015
    SooooCal/LA USA

    Re: Exposing at non-box ISOs: Why?

    Test following your slight overexposure (usually 1/2 to 1 stop over), with a very slight underdevelopment (about 10% of the time off/convert it into seconds and calculate) where you will not hit Dmax density of your film, and you will be able to print well into the highlights, with a well exposed shadow region... This is usually a sweet spot for many combinations...

    Look for a well exposed shadow area, and the max highlights on your developed film will be very slightly past greyish to black, (but only black enough that you can just see through if you held the neg up to a bright light...) Develop/process a fogged sheet and see if it looks black, but if you can see the shadow of your finger in front of the film in the direct light, you are about there...

    Test this with your film/developer combination well before your trip...

    Steve K

  7. #7
    multi format
    Join Date
    Feb 2001

    Re: Exposing at non-box ISOs: Why?

    hi paul

    i really can not add much to what doremus or steve said
    but i will suggest that you do a little film test .. you don't
    need to burn 5 or 6 or 8 sheets of film, but only a couple
    and use your darkslide to block off your negative and
    make negative as you would a test strip when making a print
    don't change your metering technique for the exposures just do as you do whenever you make a photograph ...
    do this with 3 exposures 3 sheets of film maybe ..
    1 as your meter reads it/ box speed, one over exposed 1 stop and 1 under exposed one stop
    then process the film the way you normally process your film ... 1 as the developer suggests
    your film for "box speed" 1 for 30% more than the time, one for 30% less that time.
    and make a print or scan or whatever it is you do for your negative..
    then ...
    make an exposure with a full sheet of film the combination you liked the best.
    and if you want to tweek it still, or want to see what happens in different light conditions ..
    do another "test strip"

    good luck !
    Last edited by jnantz; 5-Jun-2017 at 11:59.
    enjoy your coffee

  8. #8

    Join Date
    Sep 2014
    Montreal, Canada

    Re: Exposing at non-box ISOs: Why?


    Without getting into too much theory, to address the first question, this usually has to do with Zone System (and similar) test methods, which target a speed point 2/3 stop slower than the ISO speed. All other things being equal, the Zone System speed gives you a larger safety factor.

    Why would you want to use a lower speed (Exposure Index) than ISO? There are several possible reasons. The most valid reason would be experience. An exposure index has mostly to do with metering and printing (or digital processing) techniques. If you set your meter to ISO speed or some other exposure index, and consistently find that your negatives are under/overexposed, based on results and print quality, change the exposure index. Hard to argue with that. Other reasons for deviating from ISO speed are more flimsy: Zone System or other tests (which are generally poorly understood), tradition, equipment etc. It follows that one should probably begin with ISO speed, and deviate if required - and this should be based on the evaluation of results (note that ISO speeds are rooted in print quality). Or, begin using a lower speed which gives you a larger safety factor - but understand that is why you are doing it. Understanding why you're doing what you're doing is good. It can simplify all this, and enable you to disregard the noise.

    Also, don't get too hung up on precision. For a variety of reasons, it doesn't exist in the photographic process to the extent many people think it does.

    To answer the second question, one should generally begin by targeting a normal contrast gradient (try the manufacturer instructions as a starting point) and refine this based on how the negatives print, scan etc. This would be essentially independent of the exposure index you decide to use.


  9. #9

    Join Date
    Sep 2010

    Re: Exposing at non-box ISOs: Why?

    It has been my experience with the black and white films I have used, Plus X, Tri X, and HP5+, that they can have several usable "Normal (N)" speeds depending on development times, some more usable than others. Seek and you will find that Tri X was originally rated at 200 by Kodak, and then later, without changing the emulsion at all, only the normal development time, it was re-rated to 400. You can study all Phil Davis's excellent Beyond the Zone System writings and learn to work his Wonder Wheel, but all you really need to see there is in his chart of Tri X film speed and development times. He derived the speed of Tri X in HC 110 B at 68* for 5:00 as 64 (which does produce an excellent normal negative).

    Ansel Adams shows curves and development times for Tri X in his book The Negative and suggests that 5:00 as above yields a 160 speed but then disclaims it and says that in certain situations the "shadows need extra support" and he "places them on Zone III rather than Zone IV". This, of course, is like rating the film at 80. Fred Picker insisted on a 5:00 minute time as well, claiming that Kodak didn't know its ass from its ASA, and offered to give you your own "personal" film speed for $5 if you sent him a test neg. This was when $5 really bought something. I'm glad I studied a little Kendo and read Musashi's Book of Five Rings when I was trying to dope all this out. You need a samurai sword to cut through all the bull shit!

    I have posted this before several times and never had anyone seriously challenge my findings. Good Luck and Good Hunting!

    Years ago I learned an excellent method to find the correct developing time and EI for any film. I source was an article by William Mortensen. Mortensen wrote some excellent books and articles about basic sensitometry. The last time I did this test was when I abandoned Tri-X and switched to HP5+ due to cost about five years ago. I proceed as follows.

    I set up my trays with my favorite developer HC110B (1:31). I pull out a sheet from the package in the dark. and then when the package is sealed again I turn on the room lights. This part of the test is done under the lights. I cut the sheet into five strips and mark them 1-5 by punching holes with a paper punch. Lets say the recommended time is 5:00. I want to see 3:00, 4:00, 5:00, 6:00 and 7:00, so I throw all the strips into the developer and agitate as usual until 3:00 when I move the No.1 strip over to the stop bath. Then I pull No.2 at 4:00, No.3 at 5:00, etc. I fix, wash and dry the strips as usual. What we are looking for is the best usable film DMax value. Obviously the film has been fully exposed! When strips dry lay down a page of news print on a table in good light. Find the strip through which the news print is barely visible. That's your developing time. Now to find the film speed.

    Go outside in unchanging light conditions and expose five sheets and expose one at the manufacturers rating and then the other four at one half a stop and one stop less and one half a stop and one stop more. In the dark, develop them all together for your newly derived time. Contact print them together exposing and developing the paper for maximum usable paper DMax value. Pick out the best-looking contact print and you have your film speed.

    Because my 7:00 negative looked the best on the first test, I did the test again with 7:00 as the central developing time and found that 8:00 was indeed too dense. This HP5+ time was the same as the as the developing time I had been using for Tri-X and film speed was also the same, EI400. I have also switched to Ilfotec HC developer due to cost and availability and find it to be a clone of HC110.

    Many of the last generation of B&W gurus favored a development time of 5:00 for Tri-X and suggested an EI of 64-100. You can do the above test backwards, developing for 5:00 minutes and finding the film speed. I like 100. The image quality difference between negatives exposed at 100 and developed for 5:00 and those exposed at 400 and developed for 7:00 is quite subtle. Both could be considered "normal" or N negatives. The 100 negative has slightly greater shadow and highlight detail that only a careful, knowledgeable viewer could detect. This slight improvement might not be worthwhile trading for two stops in the field. I do routinely rate HP5+ at 100 under powerful strobe light in the studio and it produces beautiful skin tones.

    From here, if you are still with me, you can derive expansion and contraction schemes for both the 100 and 400 "normal negs". I do this by changing dilution rather than time. Make sure you have at least 1 oz. of the concentrated sauce for each 8X10 sheet or equivalent. For contractions I found that 3/4 oz. concentrate to 31 1/4 ozs. H20 yields an N-1 neg at a one stop loss in film speed and 1/2 oz. concentrate to 31 1/2 ozs. H20 yields an N-2 neg at a two stop loss in film speed. For expensions, 1 1/4 oz. of concentrate to 30 3/4 ozs. H20 yields an N+1 neg at a one stop gain in speed and 1 1/2 ozs. concentrate to 30 1/2 ozs. H20 produces an N+2 negative with a two stop gain in speed.

    If you look at the chart of Tri-X film speed in Phil Davis' BTZS book you can easily pick out the film speed in HC110B 5:00 as EI 64.

    Don't apply reciprosity exposure and development corrections for long exposures (1/2 sec. +) based on published data. Test for yourself and you may be surprised. I wasted a lot of time and effort producing long exposure negatives that were thick and flat. When I finally tested, I found no compensation was required for TXP out to one minute.

  10. #10
    Resident Heretic Bruce Watson's Avatar
    Join Date
    Sep 2003
    USA, North Carolina

    Re: Exposing at non-box ISOs: Why?

    Quote Originally Posted by Paul Kinzer View Post
    1. What is the reason to expose the film to more light than the maker recommends? Just what will this do, and why would you want to do it?
    The reason to expose to a different ISO is that the vast majority of us don't use the laboratory techniques used to determine ISO in our workflow. We don't work the way that ISO is determined, so the ISO number is just a guide. It's a starting point.

    While that's nice when you're starting out (it's always nice to be pointed in the right direction, yes?), if you want to get the most from your film you'll need to run tests to customize your exposure to work with your own personal workflow. This is why people run tests ala The Zone System to determine their own personal exposure index (PEI or just EI). And what they want from it is to know how much exposure they have to give to get a shadow density on film that they expect. What most of us want from this exercise is both control and repeatability.

    The PEI tests nail down the shadow detail end of the response curve.

    Quote Originally Posted by Paul Kinzer View Post
    2. If one does expose at a different ISO, should one then develop the film based on that ISO, or develop for the box speed?
    Neither. One should develop film to generate the highlight density that one needs. This is a separate issue from PEI, and needs separate testing to determine. In Zone System terms, after you've found your PEI, you then need to determine your N (normal) development time. And any other development times you might need, like N-1 (normal minus one stop), N-2, N+1, N+2, etc. All of this is to tune your development workflow so that, again, you can control it, and make it repeatable.

    The N development time tests nail down the highlight detail end of the response curve. Once you have both you have considerably more control of your image creation.

    All of this is just a very fancy way (and a highly accurate and precise way) to express the ancient old saw that is just as valid now as when it was first thought of:

    Expose for the shadows and develop for the highlights.

    Bruce Watson

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