f-stop test strips

Discussion in 'Darkroom Developing and Printing' started by Rich Shepard, Jul 11, 2003.

  1. Rich Shepard

    Rich Shepard Guest

    I would like to make exposure test prints using f-stop intervals rather
    than constant intervals. Purchase of an RH Designs timer is not in the
    budget. I suspect that resetting the timer for the deltas between exposure
    steps is not the most efficient way.

    How do folks do this?

    Thanks,

    Rich
     
    Rich Shepard, Jul 11, 2003
    #1
    1. Advertisements


  2. I'm not sure entirely what you have in mind, but...

    To increase a time interval by 1 stop, double it.

    To increase a time interval by 1/2 stop, multiply it by 1.414 (the square
    root of 2).

    So you could go 5, 7, 10, 14, 20, 28 seconds... at half stop intervals.


    The stops on your lens are numbered 2, 2.8, 4, 5.6... and each transmits
    half as much light as the previous one, because light transmission depends
    on area, which is proportional to aperture squared.
     
    Michael A. Covington, Jul 11, 2003
    #2
    1. Advertisements

  3. Go buy a Kodak "Print Projection Scale". It is a
    step wedge designed to show exposures with about a
    8 stop range. Not looking at mine now so I am
    guessing. It works great.
    --
    73 es cul

    wb3fup
    a Salty Bear

    "Michael A. Covington"
    message
    multiply it by 1.414 (the square
     
    WB3FUP \(Mike Hall\), Jul 11, 2003
    #3
  4. Rich Shepard

    Rich Shepard Guest

    What I would like is a more efficient method than setting my first
    exposure strip at 2.8 seconds, the next strip at 1. seconds (for a total of
    4 seconds), the third strip at 1.6 seconds (for a total of 5.6), ... and so
    on.

    Rich
     
    Rich Shepard, Jul 11, 2003
    #4
  5. Rich Shepard

    Rich Shepard Guest

    I have the Souffer Graphic Arts exposure scales -- 1/3-stops and
    1/6-stops. Yes, they are exceptionally useful as I get to the proper
    exposure in 1-2 test exposures -- most of the time, anyway.

    However, in Tim Rudman's book (as well as two others) he illustrates the
    difference between a test print at arithmetic intervals versus one at f-stop
    intervals. All the books say, "It's easy! Do it.". But they don't provide
    more explicit instructions. I assume that calculating the time deltas and
    resetting the timer between each exposure is not the most efficient way to
    achieve this -- without the exposure scales.

    However, from the responses so far I guess there is no more efficient way.

    Thanks,

    Rich
     
    Rich Shepard, Jul 11, 2003
    #5
  6. Are you sure you are not over engineering the
    solution you think you want. A "f" stop is 2x's
    the one smaller, or 1/2 the one bigger. Trust me,
    I have done the math. I do not remember the wedge
    increments on the Kodak scale, forgive me it has
    been a while since I have used it. I do know that
    if the 60 second starting exposure did not produce
    a useful starting point 30 seconds (1 "f" stop
    less) or 120 sec (1 "f" stop more) put me right in
    the ball park for a starting point. Yes, the
    result was not the "exhibition" quality print.
    That print generally required selective exposure
    (dodging and burning) and area development (dektol
    at 1:6, dektol straight, dektol at 100 degrees) to
    capture what my eye saw when the camera went click
    (the Graphic) or "Crik" (the Ashai). You need a
    good straight print to start from, but that is not
    the ending point by any means.

    --
    73 es cul

    wb3fup
    a Salty Bear

    "Rich Shepard" <-ecosys.com>
    wrote in message
    I have the Souffer Graphic Arts exposure scales -- 1/3-stops and
    1/6-stops. Yes, they are exceptionally useful as I get to the proper
    exposure in 1-2 test exposures -- most of the time, anyway.

    However, in Tim Rudman's book (as well as two others) he illustrates the
    difference between a test print at arithmetic intervals versus one at f-stop
    intervals. All the books say, "It's easy! Do it.". But they don't provide
    more explicit instructions. I assume that[/QUOTE]
    calculating the time deltas and
    there is no more efficient way.
     
    WB3FUP \(Mike Hall\), Jul 11, 2003
    #6
  7. What do you want to do, that you can't do with the Stouffer Exposure
    Guides? (Since they ARE f-stop, rather than arithmetic, it seems that
    they do exactly what Tim Rudman is suggesting.)

    Chris Ellinger
    Ann Arbor, MI
     
    Chris Ellinger, Jul 11, 2003
    #7
  8. Maybe not the most efficient, but I've been "resetting the deltas" for
    years with my old Gralab timer. Since I have to reset it for every
    exposure anyhow, I just vary the time I set it to. (e.g. about 5.5 sec
    for first exp. then about 2.5, then 3, then 5, then 6 to get approx
    eposures of 5.5, 8, 11, 16, 22 sec) I know they are only approximate,
    but it get me in the ballpark quickly and experience and guestimation
    take it to the next stage.

    I was always going to get a "better" timer, but this old beast keeps on
    ticking (the Gralab).

    Dave
     
    David Swinnard, Jul 12, 2003
    #8
  9. Rich,

    Start with a base exposure of 32 seconds for the first exposure. Cover it
    up.
    Total so far 32 seconds.
    Now work in quarter stops.

    Expose for 8 seconds that is 25 percent of 32, a quarter stop.
    Total so far 40 seconds.
    Expose for 10 seconds, 25 percent of 40, a quarter stop.
    Total so far 50 seconds.
    Expose for 12.5 seconds, and so on. Each exposure adding a quarter stop more
    exposure.

    You can use half or sixth stops in much the same way.

    rharrisa
     
    Robert Harris, Jul 12, 2003
    #9
  10. Rich Shepard

    Rich Shepard Guest

    Chris, et al.:

    I've not explained myself well. Let me try once more.

    I suppose that if one has an f-stop timer then it can be set for 1/2-stop
    intervals and will automatically expose test strips for the proper time.

    Not having a f-stop timer, I would create the test strip series thusly:
    for example, to produce test strips exposed for 2.0, 2.8, 4.0, 5.6, 8.0,
    11.0, 16.0 and 22.0 seconds I would set the timer for 6.0 seconds and expose
    the first strip (covering the rest of the paper). I would then uncover the
    second strip and expose that for 5.0 seconds. The third strip is uncovered
    and exposed for 3.0 seconds. This continues, with each stip uncoverd and the
    paper exposed for 2.4, 1.6, 1.2, 0.8 and 2.0 seconds.

    The purpose of my question was to learn if there was a more efficient way
    of generating this same series of exposures.

    Rich
     
    Rich Shepard, Jul 12, 2003
    #10
  11. Rich Shepard

    Rich Shepard Guest

    Thanks, Robert. This answers my question: there is no more efficient way
    than resetting the timer for each strip.

    There are two ways of exposing each strip. You start with the least
    exposed and cover each succeeding one at the end of the time interval. I've
    started with the most exposed and uncover each succeeding one at the end of
    the time interval. Seems to me that in either case, the most-exposed strip
    is still the product of several independent exposures rather than one
    continuous one so whatever error that causes is relatively constant.

    My curiousity is satisfied, thank you all very much.

    I will continue to use my Stouffer Graphic Arts exposure strips because
    they're much quicker and easier.

    However, on occasion I will cut a sheet of 8x10 paper into 1-inch strips,
    mark the time on the back with pencil, then expose each strip on the same
    part of the negative using f-stop time intervals. This lets me assess
    exposure time on the same important highlight area of the negative and
    that's why I asked about the timing procedure.

    Rich
     
    Rich Shepard, Jul 12, 2003
    #11
  12. Did someone just reinvent all the rules of
    photography. The marked number of an f-stop is
    the result of a mathematical calculation of the
    aperture (hole) that the light comes though and
    the focal length of the lens. The ratio is
    constant over focal length. That is why it is
    used. A f 2.8 35mm lens admits as much light to
    the camera as a f 2.8 135mm. The ratio, if you do
    the math, produces an area 50%, or 200%, of the
    preceding, or succeeding number in the series.

    To accomplish this with a timer is a royal pain in
    the tush. Place the test strip on the easel,
    uncovered and make the minimum exposure of the
    series, say 4 seconds. Cover a portion of the
    strip and expose for the total time that preceded
    the step, 4 seconds. Cover a portion and expose
    for 8 seconds, cover a portion and expose for 16
    seconds. Let's leave it at that. You now have a
    strip that has sections exposed for 4, 8, 16, and
    32 seconds. Each of the exposures is one stop
    away from the other.

    The step wedges that have bee referred to in this
    thread simplify life, and result in more accurate
    test prints. They make life simple by making one
    exposure for a fixed amount of time. I do not
    have to remember was the last exposure 4 seconds
    for a total of 8 etc. They improve the testing
    process by allowing you to place the step wedge to
    cove the critical point of interest, and determine
    a trial exposure there, not over a wide portion of
    the print that may or not be representative of the
    exposure desired at the point of interest.

    Just one man's opinion though, It has worked well
    me for more than 50 years, you have to make your
    own mistakes to decide what works best for you.
    --
    73 es cul

    wb3fup
    a Salty Bear

    "Rich Shepard" <-ecosys.com>
    wrote in message
    Thanks, Robert. This answers my question: there is no more efficient way
    than resetting the timer for each strip.

    There are two ways of exposing each strip. You start with the least
    exposed and cover each succeeding one at the end of the time interval. I've
    started with the most exposed and uncover each succeeding one at the end of
    the time interval. Seems to me that in either case, the most-exposed strip
    is still the product of several independent exposures rather than one
    continuous one so whatever error that causes is relatively constant.

    My curiousity is satisfied, thank you all very much.

    I will continue to use my Stouffer Graphic Arts exposure strips because
    they're much quicker and easier.

    However, on occasion I will cut a sheet of 8x10 paper into 1-inch strips,
    mark the time on the back with pencil, then expose each strip on the same
    part of the negative using f-stop time intervals. This lets me assess
    exposure time on the same important highlight area of the negative and
    that's why I asked about the timing procedure.

    Rich
    [/QUOTE]
     
    WB3FUP \(Mike Hall\), Jul 12, 2003
    #12
  13. Rich Shepard

    G.P Guest

    So 50 seconds + 12.5 seconds = 62.5 seconds, which is almost double the
    base exposure of 32 seconds, that means there are only about 3 quarter
    stops - instead of 4 -separating an exposure of 32 seconds and another of 64
    seconds, which is obviously incorrect. Full stop exposure times increase or
    decrease exponentially (1,2,4,8,16,32.....), it follows then that fraction
    of stops increase or decrease exponentially, also. one quarter stop above
    32 seconds would be an extra exposure of 6 seconds (aprox) and the factor to
    find and exposure 1/4 stops higher that 32 is: 2^0.25 = 1.1892. In
    general, the factor for "n" stops more time exposure is: 2^n , where "n" can
    be whole or fractional (1/2 stop n=0.5 factor being 2^0.5 = 1.414, 1/3 stop
    n=0.333 factor being 2^0.333 = 1.2596, 1/4 stop n=0.25 factor = 1.1892,
    etc).

    The above example then should be:

    32 seconds base exposure + 6.054 seconds, + quarter stop
    Total = 38.054 seconds (approximate according to the timer in use)
    expose for 7.2 extra seconds, + quarter stop
    Total = 45.254 seconds
    expose for 8.56 extra seconds, another + quarter stop
    Total = 53.816 seconds
    expose for 10.184 extra seconds, + quarter stop
    Total 64 seconds, just what we expect after exposing for 4 quarter stops
    above the base exposure of 32 seconds.

    And that is the reason fractional f/stops test strips are cumbersome to do
    dialing increments of time with the timer.

    Guillermo
     
    G.P, Jul 13, 2003
    #13
  14. Rich Shepard

    Nige Guest

    I was wondering if everyone was making it more difficult than needed to be.

    If I have no idea when looking at the neg, I'll do a 2sec timer step for 4
    steps that gets me 2,4,6,8 secs, then with the last one (using a Paterson
    test strip thingy) I'll either just give it another 2sec zap or change the
    timer to 4secs to have the last one at 12secs. The majority of the time
    I'll do 5sec then 1sec zaps for 5,6,7,8,9 cause I know it will be in that
    range.

    Doing 4-5 stop exposure ranges tells me you need to contentrate a bit more
    on exposure and development.

    Cheers, Nige
     
    Nige, Jul 13, 2003
    #14
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.