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Thread: how to do the math for speed film test

  1. #21

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    Re: how to do the math for speed film test

    Quote Originally Posted by fralexis View Post
    So on a 4x5 view camera that means extending the bellows all the way to it's maximum?
    No the exact opposite is what they mean... to focus at infinity, you aim at a distant object. You will find the 4x5 view camera bellows is closed up most of the way when you are at the right focus position for a speed test.

    Then without changing the focus position, fill the ground glass with the blurry test target.

    If you did it the other way, and you stretched out the bellows... that could explain why your test seems to indicate 32 speed.

    --- There isn't one cheat sheet reference for film speed testing because everyone does it differently and everyone has their own write-up they like ---

    I have my own ideas too, but I don't want to make things complicated for you right now.

    If the bellows extension was your problem, you might test again focused at infinity.

    Otherwise, you could do no harm shooting a 200 speed film at 32. I once had a test problem and found 64 speed for a 400 speed film. I went around for a year shooting that film at 64 and got some of the best pictures of my life.

  2. #22
    Drew Bedo's Avatar
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    Re: how to do the math for speed film test

    Many years ago I got ahold of some medical imaging film, EktascaB. We used it at work to image CRT traces . To use it in an 8x10 camera at home I loaded a few film holders and did some test shots of the swing set in our back yard.

    I figured it was pretty fast to capture fleeting spots on a CRT. I set up a series of exposures by choosing a shutter speed and aperature correct for the lighting assuming a film speed of 50 and pulled the slide for one exposure. Then inserted the slide 1/3 in and made the same exposure. Next the slide was pushed in to the 2/4 position (about) and another exposure was made at half the first shutter speed.

    The one sheet of film had been exposed at an assumed ISO 50, 100 and 200. Iflipped the film holder did did the same at 200, 400 and 800. When the film was developed, it seemed to be good if rated at ISO 200, and that is where I shot it for several years.

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  3. #23

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    Re: how to do the math for speed film test

    I want to thank all those who offered suggestions and advice. Each post had something important for me. I had a very kind private message that gave me some good directions. I followed this directions and determined tat my film speed should be between 64 and 100 iso. The resulting negatives were just what I wanted. I stuck with the 100 iso for convenience sake. I am attaching a partial scan of one negative to show you what I came up with. Perhaps it isn't perfect, but it is a far cry better than what I had.

    Now a problem I have has to do with printing. The scan looks great, but my print comes out very grey and muddy. There is no "punch" or contrast to the print. There are no deep rich darks as in the scan. I opened a new box of paper. I am using Arista edu glossy RC paper on a Beseler 45s enlarger with a color head. I have the contrast at level 2. The exposure was at f22 with 22 seconds. I am developing with Arista paper developer. My safelight is a Thomas Duplex Super Safe Light. I am sticking with the basic recommendations from the manufacturer until I get a handle on it. It obviously is my technique at printing. Any ideas?

    Thanks again!

    Click image for larger version. 

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    Alexis

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  4. #24
    David Schaller
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    Re: how to do the math for speed film test

    Less time, higher filter. Increase the magenta in the filter head. Try the equivalent of a 3. Don't feel that everything has to be aimed for 2 or 2.5.

  5. #25

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    Re: how to do the math for speed film test

    Quote Originally Posted by Bill Burk View Post
    No the exact opposite is what they mean... to focus at infinity, you aim at a distant object. You will find the 4x5 view camera bellows is closed up most of the way when you are at the right focus position for a speed test.
    Or you can measure the distance from the lens board to the film plane and set it for the lens' focal length........L

  6. #26

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    Re: how to do the math for speed film test

    I just wanted to give an update. I followed all your suggestions and carefully made tests, experimented and still was unable to get a print that was not muddy and lacked deep black shadows. I was ready to just about give up. Then I though that it could nt hurt to make another experiment.

    I am shooting 4X5 Arista EDU ultra asa 200. I found my personal speed should be about asa 100. I was developing my paper, also Arista Ultra EDU in Arista paper developer 1:9 for 1.5 minutes and the rest as usual

    I made one change, and began using Ilford Multigrade paper developer and magic happened. Now I am getting beautiful deep shadows, wonderful mid-tones and good highlights. So rather than formulas and negative work, exposure and so forth, all along it was using a paper developer that didn't produce good results for me. So I learned something. Thanks for your input.

    Alexis
    Alexis

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  7. #27

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    Re: how to do the math for speed film test

    Following Michael R's point about 1/3 stops, could it be that you actually increased exposure 1/3 stop each time, but mistakenly counted whole stops when getting to your Z-I neg? If so, would that have actually been f32 you set and result in a 100 speed?

  8. #28

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    Re: how to do the math for speed film test

    Quote Originally Posted by fralexis View Post
    I truly appreciate all your great answers and advice. However, my brain doesn't think in an analytical manner and all the information is confusing to me. In the end, I suppose I just need a simple yet clear method for determining my film speed. I know there are endless variables, but I can't process all that at my present stage of learning. All of you are far advanced in this process and I am just a newbie at the technical side of things.

    Does anyone have a very simple and clear method for getting film speed? Then perhaps I can experiment and start thinking about the variables. Thank you so much!

    Alexis


    Years ago I learned an excellent method to find the correct developing time and EI for any film. I think the 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), now Ilfotec HC (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 through the film base plus fog negative rebate area. 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 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 or now HP5+ out to one minute.
    Last edited by Neal Chaves; 30-Aug-2017 at 12:05.

  9. #29

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    Re: how to do the math for speed film test

    A little late to the game, but my personal EI for Arista 200 is 40. Works well. Thanks for the tip on the developer, I'm going to try it.

  10. #30

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    Re: how to do the math for speed film test

    Quote Originally Posted by fralexis View Post

    Does anyone have a very simple and clear method for getting film speed?

    Alexis

    - metering a pair of black socks, with box speed
    - exposing 4 stops less than given by the meter ( not to forget adding bellows factor)
    - developing to recommended time

    Should give nearly white socks with little drawings in the negative (zone 1, correct filmspeed)); if not - same procedure with slightly corrected film speed (longer or shorter exposure).

    Finding zone 8 (correct development):
    exposing a white t-shirt with 3 stops plus than given by the meter will do the simple but somehow clear trick and should give a black shirt with some drawings in the negative..

    Ritchie

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