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Thread: Testing film? Using a densitometer?

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    Testing film? Using a densitometer?

    Newbie question. Getting ready to shoot my first LF 8x10. Using HP5 film. Most likely using Ilford Ilfotec HC developer. Reading about calibrating film and and using a Densitometer. Is this still necessary if I am using the same developer and Film? I don't have a densitometer and my head exploded when I tried to understand the process. I also have access to a 4x5 camera and HP5 film for testing.(cost) Is there a easier way to test? thanks

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    Randy Moe's Avatar
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    Re: Testing film? Using a densitometer?

    You are new here. Good question and by asking you trigger the automatic site search for similar results.

    They are listed at the bottom of this page.

    Shoot some 4x5 first...

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    bob carnie's Avatar
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    Re: Testing film? Using a densitometer?

    Kodak had a nice tip for evaluating your negatives.

    Place your negative over top of a newspaper. If you can just read the type through the highlight area, and there is detail in you shadow area you pretty much have a good negative.

    After 40 years of printing for others I still find this to be good advice.

    Bob

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    Peter De Smidt's Avatar
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    Re: Testing film? Using a densitometer?

    If you have access to a densitometer, then it's really not that hard to simple exposure/development tests. Fred Picker's Zone VI Workshop, probably available at your local library, lays out a good method, although he works in 1/2 stops, while I prefer 1/3 stops, as that mirrors available film speeds.

    It's important to know that exposure has the greatest effect on darker areas of your scene. If you don't give enough exposure, they won't have any detail. Conversely, development time/temp/agitation affects the brighter areas of your scene more than the darker ones. As a result, you want to give your film enough exposure to get detail in your scenes darker areas, and you want to develop such that you have good tonal separation in your negative, and that the highest densities are appropriate for the medium you're going to print with. For instance, many alternative processes need more negative density than does printing on silver gelatin paper.

    Assuming you're going to be taking landscape photos, and have a spot meter, do the following. Load some film holders. Set up a black mat card in shade, as you're gong to test film speed first. A standard black poster board works well. Meter the card, making sure that it is evenly lit. Make sure that there is nothing too bright in the background of the photo. Focus your camera on infinity, and aim it so that the card is in the center of the frame. You focus on infinity so that bellows extension doesn't affect the results. It doesn't matter that the card will be a little fuzzy. Set your meter reading for box speed, i.e. set it at ISO 100 for a 100 speed film. Measure the card. Let's say it gives f/8 at 1/60th of a second. Exposing at that setting would give a middle gray, known as Zone V in Zone System parlance. In this case, though, we're looking for Zone I, the lowest amount of light that'll still record well on the negative. To place the card on Zone I, you have to close down the aperture 4 stops, give 4 stops less exposure time, or a mixture. I prefer to work in aperture stops. Thus if the card reads f/8 at 1/60th with the meter, you'd set f/32 at 1/60th on your lens, placing the card on Zone I. Expose your negative. Now expose a couple more negatives opening the aperture by 1/3 stop each time.

    Develop the film according to your best guess at the proper development. Read the film base + fog, the unexposed area of the film. Now read the densities of the card for each of the negatives. The negative shot at box speed will have the least density. You're looking for the negative that gives a Zone I density of at least .1 above film base plus fog. (That's traditional zone system practice. I prefer 0.15.) If the card shot with your first negative gives the proper density, then your film speed is what the manufacture says. Congratulations! That's not all that common. Usually the true film speed is about 1/2 of the advertised one. But if the desity is to low, move to the next negative, which should be slightly more dense. Since you gave 1/3 stop more exposure, this negative represents rating your film 1/3 stop slower than box speed. (So if box speed is 100, this negative would represent 80.) Keep reading negatives until you get the proper speed. Each one represent your film being 1/3 stop slower than the one before it.

    Now you know your normal film speed. The next step is to fine tune your development time.

    Set up a matte white card in sun. Meter the card. You want to place it on Zone VIII, a bright area with detail. Focus on infinity and take a meter reading, using the ISO setting that you determined in the earlier test. Setting the shutter at that setting would give a middle gray, Zone V. To get to Zone VIII, open up 3 stops from the meter reading. Expose 3 negatives at that setting. Now develop the sheet of film. If you're printing with a diffusion enlarger onto silver gelatin paper, you want a Zone VIII density to be about 1.3 above film base plus fog. If the negative density is to low, try developing another sheet for 20% more time. If the negative density is too high, develop for 20% less time. Use more sheets of film to narrow it down, if needed. After awhile, you'll get pretty good at guessing the proper development time from using one sheet of film.

    You now have your Normal (N) film speed and development time.
    "Why can't we all just get along?" President Dale, Mars Attacks

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    Re: Testing film? Using a densitometer?

    Quote Originally Posted by AndyL View Post
    I don't have a densitometer and my head exploded when I tried to understand the process.
    Me too. You might find this article helpful: Testing B&W Film

    Note that "almost everyone" who does rigorous film testing ends up shooting at one f/stop slower than box speed: 200 for HP5+ and TMY, 50 for FP4+ and TMX, etc. The more important issue is determining the development times which work for you.

    If you don't care to load the Zone System into your brain, you might also find this even more helpful: A Simpler Approach. It's what I use after many decades.

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    Re: Testing film? Using a densitometer?

    Quote Originally Posted by Ken Lee View Post

    Note that "almost everyone" who does rigorous film testing ends up shooting at one f/stop slower than box speed: 200 for HP5+ and TMY, 50 for FP4+ and TMX, etc.
    And there is a simple reason for that, which almost nobody wants to know about, unfortunately. Suffice it to say if you plan on finding an EI using a Zone System-type test, you can skip that part and simply reduce film speed by 2/3 stop (or round it to either 1/2 stop of 1 stop).

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    Randy Moe's Avatar
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    Re: Testing film? Using a densitometer?

    Quote Originally Posted by Michael R View Post
    And there is a very simple reason for that, which almost nobody wants to know about, unfortunately. Suffice it to say if you plan on finding an EI using a Zone System-type test, you can skip that part and simply reduce film speed by 2/3 stop (or round it to either 1/2 stop of 1 stop).
    Well we are curious now. Do tell!

    I simply go by the rule to overexpose film and underexpose digital.

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    Peter De Smidt's Avatar
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    Re: Testing film? Using a densitometer?

    Quote Originally Posted by Michael R View Post
    And there is a simple reason for that, which almost nobody wants to know about, unfortunately. Suffice it to say if you plan on finding an EI using a Zone System-type test, you can skip that part and simply reduce film speed by 2/3 stop (or round it to either 1/2 stop of 1 stop).
    Often that works, but with TMY in my system it doesn't. My EI using Zone System testing is 500.
    "Why can't we all just get along?" President Dale, Mars Attacks

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    Re: Testing film? Using a densitometer?

    Correct me please if I am wrong, but one reason (according to Phil Davis) is that a standard gray card is not middle gray or Zone V under typical lighting conditions. See The Myth of the 18% Gray Card

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    Re: Testing film? Using a densitometer?

    Randy:

    The Zone System speed point is based on the pre-1960 ANSI/ISO standard that included an extra 2/3 stop "safety factor". The safety factor in the standard at that time was larger because historically meters, shutters etc. were less precise. The safety factor was then revised downward by 2/3 stop to account for improvements in equipment, and the increased popularity of smaller film formats. The Zone System was never updated. It is important to note the safety factor is just that. It is not, in and of itself, based on print quality.

    Since the Zone System speed point includes the larger safety factor than current ISO ("box" speed), all you're doing when you do a Zone System EI test, is confirming the difference in the safety factor. This is important, because it means most people actually misunderstand the Zone System EI test, and therefore misinterpret the results. When you do a Zone System EI test, you're not actually revealing new information. You're not finding a "better" speed in terms of tone reproduction quality, you're not finding a "truer" speed, and also importantly, you're not finding a speed based on your own working methods (which most Zone System books would have us believe).

    There's some more theory on this, and flare is important too, but I'll stop there pending attacks (that's usually what happens).

    All this to say, barring extreme procedures and special purpose developers, 9 times out of 10 people will find personal ZS EIs in the range of 1/2 to 1 stop slower than ISO speed. Now you know why.

    Peter's example is good to show there can be exceptions, although his case does seem odd to me. When I ran ZS tests on TMY-2 I got exactly what the theory predicts.

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