F-Stop Meathod of Timing Exposure

Discussion in 'Enlarging' started by bmac, Nov 1, 2002.

  1. bmac

    bmac Member

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    There has been a little discussion about this meathod of printing. Can someone give a bonehead sleep deprived new dad a basic explanation?
     
  2. Jorge

    Jorge Inactive

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    There are two ways to measure exposure, one by the amount of time the paper is exposed and the other by the amount of light the paper is exposed to. In the f stop methid you keep constant the time and you vary the "amount" of light. I tried it and found very confusing and complicated. Since I am old school I learned to judge manipulations by time...ei, lets burn 3 more sec here, dodge 5 sec there....for the life of me I could not figure out what a 1/4 f stop would do....but some people seem to like the method.
     
  3. Jim Chinn

    Jim Chinn Member

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    If you can find a copy of Eddie Ephraums "Creative Elements- Darkroom Techniques for Landscape Photography", he goes into depth about using this method and includes an F.Stop exposure table which allows you to determine time in 1/4 stops. Of course this asumes that you are using a timer that can operate in tenths and hundreths of a second.

    It is really much more precise, and as you use it you begin to look at test strips and prints and it bcomes easy to determine burning and dodging times and adjustments in exposure.

    I believe it is still available there was a timer called a Nocon that could be programmed to adjust the exposure time based on initial time and the desired f-stop change that was entered.

    More modern F-stop timers adjust can adjust the light as well as the time.

    I use the more cumbersome method of going to the table and inputting the new time in a digital timer. The formula is also in the book.
     
  4. Les McLean

    Les McLean Subscriber

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    RH Designs, a UK company, manufacture an excellent fstop timer that is simple to use and offers a dry down factor, two channels for split grade printing and a compensating feature for those who use cold cathode enlargers. I have used this companies products since the mid 90's and can certainly recommend them
     
  5. ann

    ann Subscriber

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    Several years ago I began teaching my students to burn and dodge using the conspect of f stops. This is how our cameras work and it seemed logical to use the same logic in the darkroom. i.e. in the field with snow we open up 1 to 2 f stops to insure we had white snow, not gray. White highlights on a print would be burned down using the same logic. Paper white highlights would reguire about 2fstops more light than the inital exposure to bring them to middle gray. How much is an artistic decision.
    It may sound more involved than it really is, once people start thinking that way it is amazing how quickly they catch on.
    Check out Eddie's book, if I remember Tim Rudman also talks about f stop printing in his Master Photograhpers book. ( I thought I was so clever, until i found out in Europe they make a timer and this method is not so strange). Works just as easily with dodging.
    The biggest stumbling block is doing the math in your head, however, after awhile it becomes second nature.
     
  6. Doremus Scudder

    Doremus Scudder Member

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    Time for my two-cents worth: I have for years used a hybrid of the f-stop and time methods: I figure exposures by percentages. For me, the log and square-root-of-2 calculations that one has to do for the f-stop method are superfluous. I find it much easier to alter exposure and figure dodging and burning by increasing or decreasing exposure by a percentage. Of course, a 100% increase is a one-stop increase. Conversely, a 50% decrease is a one-stop decrease. Intermediate values are easily figured, and with just a little practice, one learns to estimate the effect of, say, a 10% decrease in exposure.

    Test strips can be made to approximate, for example, a progression of 20% increases. For example, 10 sec. (+20% =), 12 sec. (+20% = approx), 14 sec. (+20% = approx.), 17 sec. (+20% = approx.), 20 sec.... etc. Ten per cent strips are just as easy to figure. No logs, no square roots, no problems. I use a metronome as a printing timer and, when making the above test strip, would simply count 10 sec, cover the first stripe, count 2 sec., cover the next stripe, count 2 mor sec., cover the third stripe; count 3 sec..... The progression is then 10+2+2+3+3+4+5.... Easy to remember, and, if need be, post close to the enlarger for reference.

    This method is also extremely helpful when making a different size of a print already made. Once the basic exposure has been arrived at, all manipulations can be converted to percentages and refigured for the new print. If the original print has a basic exposure of, say 30 sec. and I burned an area for 6 sec., that would be 20%. If the new print has a basic exposure of 20 sec., then 20% of that would be 4 sec. Easy

    Frankly, I'm surprised people go to all the trouble of figuring, making charts and computer programs to compensate for the unwieldy f-stop numbers and the inverse square law when simple percentages accomplish the same thing with a minumum of calculation. After all, it is the final image we are interested in, right...

    Regards, ;^D)
     
  7. edbuffaloe

    edbuffaloe Member

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  8. bmac

    bmac Member

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    Thanks for the link Ed. I am getting about 35 sec main exposures on my D2 with a El Nikkor at F11 making 11X14 prints from 6X7 negs...
     
  9. LD Horricks

    LD Horricks Member

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    I second the recommendation for RH Designs f-stop timer, its a pleasure to work with... Yes, Tim Rudman does speak about his use of this method in his book and on several other photo forums...in addition Robert Mann also discusses a version of this method on his <www.parisdarkroom.com> site. For me it has always made more sense to think in terms of f-stops, and with the introduction of the f-stop timers life is much easier for me in the darkroom.

    LD Horricks
    Prague, Czech Republic
     
  10. LD Horricks

    LD Horricks Member

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    Robert Mann's site is www.parisdarkroom.com

    For some reason my prior post didnt include thid info even though I typed it in...maybe because of the parenthesis I used...I'm a computer luddite.
     
  11. Stuart

    Stuart Member

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    I third the rcommendation for RH Designs Stop Clock.I picked one up six months ago and it has made a hugh improvment to my printing,especeily when it come to split grage printing.
    Go to www.rhdesigns.co.uk have a look,you won´t look back.
     
  12. Kirk Keyes

    Kirk Keyes Member

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    It's not "more precise", it's just a different way to measure the light light Jorge points out. It may be more intuitive for some, but it is not more precise.
     
  13. Dave Miller

    Dave Miller Member

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    It's basicly the same way that we control the light when we expose our film in a camera, anyway is there another way to print?
     
  14. thefizz

    thefizz Subscriber

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    I will admit that when I first tried f-stop printing it seemed too much trouble but I persevered at it and now I am very happy I did.

    When making a certain size print, I will do a few test strips in f-stops and find a good base time along with dodging/burning times. Then for example if I wanted to do a larger size print I find a new base time which will be longer but I can easily calculate the dodging/burning times as I already know how many + or - f-stops are needed. I found it saved on paper.

    Hope that makes sense.

    Peter
     
  15. BradS

    BradS Subscriber

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    Hi Brian,
    I don't know anything about the f-stop method. Just wanted to say, hi and welcome back.


    Oh...and...ah, what's this about "sleep deprived new father"? Sounds like congrats are in order. Congratulations!
     
  16. Paul Howell

    Paul Howell Member

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    For those who may to try an exposure meter and you don't to pay for a RH meter until you have a chance to try one find an old Spoto Matic meter. As already noted you find the time for max black for your paper and then you meter for shadow details. I have a unit that I bought in the 70s, it meters for both shadow details and paper grade. Although not very sensitive it will give you a good working print. I seldom use mine, I tend to prefer to set my F stop and work with time for print control, but I use it when I am making 5X7 proof prints from 35mm. Very basic unit, certainly not as senstive nor the features of an RE or other modern meters.
     
  17. John Cook

    John Cook Member

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    Presuming (1) that you work mostly in similar light (daylight, nice weather, geographically near your hometown), (2) that either you can operate an exposure meter or have an automatic camera, and (3) that your materials and processing are fresh and consistent, always using the same film, paper and developers, your negatives will all have nearly the same density.

    Full-frame prints of the same paper size will therefore all print at about the same enlarger exposure.

    If you have a good memory or keep notes, the approximate enlarger f/stop and exposure time should be known before you begin printing. Therefore, your test strip experimentation need be only very narrow, just to fine-tune the image.

    This can be done by making three or five bracketed small partial prints. For example, if your final print size will be 8x10, cut up a sheet into four 4x5's and expose one at a time in the same spot on the 8x10 easel at the same enlarger timer setting but a different half or third f/stop.

    This technique does not lend itself to the traditional additive method of moving an opaque cardboard along a single test strip for sequential exposures.

    The major point of this f/stop method is that the enlarger bulb takes a moment to warm up and begin to glow after the timer is activated. It then takes another moment to cool down and extinguish after the current is shut off.

    Therefore, a series of ten 1-second exposures does not add up to one 10-second exposure. Rocking the f/stop eliminates this discrepancy and is much more accurate.
     
  18. dancqu

    dancqu Member

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  19. Nicole

    Nicole Member

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  20. Dan Henderson

    Dan Henderson Member

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    I've had good success determining the basic exposure time using a scheme I read in Black and White Photography by, I believe, Julien Buselle. The exposure times are 5, 2, 3, 4, 6, and 10 seconds. This works out to total exposure times for each strip of 5, 7, 10, 15, 20, and 30 seconds, which are (approximately in a couple of cases) 1/2 stop apart. I dry the test strip and evaluate the basic exposure time by eye. The differences are enough that if one seems too light and the other too dark I can go to the 1/4 stop time between the two. The progression was easy for me to memorize, and as other posters have observed, the logic of f/stop printing is in harmony with how we evaluate light when exposing film. Now to get my hands on one of those great sounding f/stop timers from England...
     
  21. Dave Miller

    Dave Miller Member

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    I think that what we may be missing in this discussion is the acknowledgement that with an f-stop timer the system is extremely easy to operate, whereas without one it is quite cumbersome, requiring reference to tables, and/or calculations. I felt that since I was going to stop counting elephants and purchase an electronic enlarger lamp switch, it might just as well be an f-stop timer.

    My method is to standardise on a 10 second base exposure, and to vary the lens aperture to control the light required to obtain my base exposure. I define this base exposure as that minimum exposure required by most of the print. I may dodge very small areas to reduce localised exposure further. I then add further exposure to those areas that need it, in fractions, or multiples of the base exposure, that is in f-stops. In other words I think in f-stops, not seconds.

    Should I choose to reprint at a different print size, (or onto a different paper), then a simple calculation is used to establish the new base exposure, and then all other exposures of the burning and dodging regime follow exactly the same f-stop sequence as the original print. I expect to get an identical print from this method on my 3 inch RC test print as I do on a 20 inch finished Fibre print. It is this ease and flexibility that is the attraction of this printing method for me.

    Whilst I see little point in an established and successful printer struggling to adapt to this method, I would advocate those new to printing to adopt it from the start of their training.