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Thread: Personal Film Speed

  1. #1

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    Feb 2002
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    Personal Film Speed

    Hi, I have been looking at Barry Thornton's excellent web page and have performed th e speed test descibed there (summary: photograph grey card at zone I, bracket, p rint step wedge from blank frame to assess max black, match prints from brackete d zone I frames to max black) and found that I should be rating Ilford FP4+ at 2 /3 - 1 stop faster (ie: max 250 ASA).

    Barry Thornton says that he has personally overseen hundreds fo these tests and all of them result in a lower ASA rating, typically from 125 to 64.

    This has got me worried - have I done something wrong (I'm good at that) or has anyone else got a higher speed rating?

    Neil

  2. #2

    Join Date
    Jun 2000
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    193

    Personal Film Speed

    this is strange...

    with FP4+.. my negatives are better if rated at 100.. both in 4x5 and 120 sizes....in D76...

    btw.. I think something to do with shutter speed, developer, temperature, time, and agitation pattern...

    in my opinion that's your shutter.. if you find out some combination(s) worked well for YOU... stick with it and don't bother... only the results count..

  3. #3

    Join Date
    Apr 2000
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    149

    Personal Film Speed

    You are actually asking this question on the wrong forum, but in all my experience with testing film, I have only once or twice seen a film rated above its manufacturer's suggested film speed. One example is T-Max 400 developed in PMK+, which I rate at 640. I would note that 250 is twice the recommended speed for FP-4+, which is quite remarkable.

    That said, your particular camera, meter, lighting, water quality, developer formula, agitation technique, atmospheric pressure, and favorite beer may create the right conditions for you to successfully rate FP-4+ at 250. You don't say what developer you are using.

  4. #4

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    Apr 2000
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    Personal Film Speed

    Oops. Sorry about that "wrong forum" comment. I forgot which forum I was on...

  5. #5

    Personal Film Speed

    My experience is that subjective measurements such as "as dark as" are very difficult. It can be difficult to discern a small change is black levels. When I did my first film test I was surprised to find that I had a speed faster than the manufacturer. After the test strips dried and I looked at them in varying light conditions I was about a half stop less than manufacturer rating.

  6. #6

    Join Date
    Nov 2001
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    22

    Personal Film Speed

    in all the speed tests, including "the negative", phil davis' book, and in dealing with howard bond, densitometer measurements are the most accurate for determining the correct speed test. i am not familiar with the web page that you quote, but i'm sure you can borrow a densitometer for your speed tests. this is certainly the way to assess black since matching prints is very difficult. howard

  7. #7

    Join Date
    Jul 2001
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    60

    Personal Film Speed

    It could be your meter as well as the other variables mentioned. The EI's with one of my meters are always higher. As long as the negatives you get give you a full value range on a consistent basis, it really doesn't matter what EI you use. Just be aware that if you change equipment --shutter, meter, etc.-- your results may change.

  8. #8

    Personal Film Speed

    Hi! I just read Barry Thorntorn's article, and it's good. I've been changing darkroom lately and have started to recalibrate as I've changed my developing methods. (I've started to use my CombiPlan again, as I don't have access to a Jobo anymore.) This is in short the method that I use. It doesn't differ much from what Barry describes, but there are some points where it really differs and I'll point those out as I ramble along. First some commonground basics: The exposure point should be 0.10 (1/3 step) above base+fog. That exposure determins the film sensitivity. Load up three cassettes with 6 sheets of film. I use a grey card (as Barry), but I've seen receipies where a black piece of carton is used. Place the gray card in an open shadow where it is evenly lit. Use a good backlight hood and see to that there are no bright areas surrounding the gray card. Focus on infinity. Meter the gray card and note the exposure value. What we are looking for is an exposure that is 3 1/2 steps below what the meter says. I would personally set the ISO setting on the meter to 80 as a start when testing FP4+. (But that's me.) Now, we are not sure if our personal exposure index is at 80 ISO, so we want a reference. First we need a blank exposure, so there goes the first sheet of film. For sheet 2, expose 4 1/2 steps less than the meter indication. (Use sensible values. If you normally use f/22 - f/32, do so now as well, instead of f/90.) For sheet 3 open up 1/2 step so that you are at 4 steps less than the metered value. Sheet 4 should be at 3 1/2 steps below, sheet 5 at 3 steps and sheet 6 at 2 1/2 steps below. Keep notes of all the values that you used, as this makes the final evaluation easier. Now you got five exposed sheets and a blank sheet for the base+fog reference. Develop all the sheets, prefererly in the same run. Be sure to include the blank sheet in the process, as you need it to be in the same run. Develop at normal time with everything normal, as you should have done with those once-in-a-lifetime-pics. And do try to keep track of which sheet is which. There are three ways of evaluating the test exposures, namely with a densitometer, or comparing with the aid of an ND-filter with density of 0.10 and lastly with a good stable timer for your enlarger. Densitometer: With a calibrated densitometer you first meter the blank sheet for the base+fog value. Then you find the sheet that has 0.10 more density and you are done. Comparison with an 0.10 ND-filter: You obviously need a 0.10 ND- filter for this. And here is where this method really differs from Barry's. You should use the hardest grade paper that you can lay your hands on. Grade 5 is excellent, but hard to find. I use Ilford MG with filter 5. Why? Well, the hard paper makes it easier to spot the difference in between the slighly different exposures. It is much more visible than with a grade 2. First contact copy the blank sheet with the ND-filter on top. Find out which time is needed to produce a middle gray. Note that time and use it to contact copy the other 5 sheets, without the ND-filter. Now compare these 5 contact prints and find out which one it is that is the closest match to the base+fog+0.10 contact print. The third method does need a very good and stable (repeatable) timer: This method is somewhat more sensitive to stray light in the darkroom, so try to turn off as much darkroom light as possible. Now, with the blank negative in the enlarger, find a suitable height and aperture that produces a middle gray tone on a hard printing paper with a time of 10.0 seconds. Mark out this paper. (Cut a corner or something.) Now, with the same height and aperture, expose the other 5 negatives for 12.5 seconds. (The 25% is to simulate a density increase of 0.10.) Develop all the six papers at the same run. (It only needs to be e.g. a 8X10" sheet cut in six pieces.) When developed, fixed, washed and dried, you rank the 5 unmarked pieces from darkest to lightest. The darkest is the one that received 4 1/2 steps below your meter value when you shot the test sequence. The densitometer method is the fastest and best, followed by the ND- filter method. (I use the ND-filter method, as I don't own a densitometer.) The timer method works, but is a bit more tricky and depends upon a very reliable timer. Finally, what does these exposures give us. Say that I want to find the exposure index of FP4+. I started by guessing at 80 ISO. The first exposure was blank. The second was exposed at 4 1/2 steps below the metering point, i.e at 160 ISO. The third at 110 ISO, the fourth at 80 ISO, the fifth at 55 ISO and the sixth at 40 ISO. I learnt these methods from a swedish book written by Lars Kjellberg. He, in his turn gathered information from e.g. Phil Davies et.al. End of my longest post... Hope that this helps someone. And yes, it is easier to do with roll film. :-)

  9. #9

    Personal Film Speed

    The higher rating may be due to your meter. Some meters, like Pentax, are set to read higher than most other meters. My Pentax meter reads 1 1/3 stop over my Sekonic meter. My normal speed for HP-5+ is 500 with the Pentax, but 200 with the Sekonic.

  10. #10

    Join Date
    Feb 2002
    Location
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    Personal Film Speed

    Ed - do you think the difference could be attributed to English Real Ale?

    William - intersting, I do use a Pentax digital spot meter.

    Thanks to everyone else who has contributed a reply.

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