Test strip times and printing times

Discussion in 'Enlarging' started by Todd Barlow, Aug 4, 2006.

  1. Todd Barlow

    Todd Barlow Subscriber

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    I have seen the Fred Picker printing video where he makes a test strip using 3 second exposures and instead of selecting a 21 second print exposure he will use 7 x 3 second exposures.

    I have been trying the F-Stop method of making test strips (using a digital timer, not using technology like the RH Design products).

    If you are also using the F-Stop method:
    1) Do you make one expsoure for the total time? or
    2) Do you repeat the series of exposures that made up the test strip? or
    3) It doesn't really make a difference

    Todd
     
  2. Donald Miller

    Donald Miller Member

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    Todd, Let me begin by saying that seven three second exposures do not equal the same as a single twenty one second exposure. The reason is that lamp start up and dimming effects enter into the multiple exposures.

    In defense of Fred, F stop timing was not spoken of when he was with us. He also apparently did not understand the divergence from a total exposure in the method that he used.

    Thus it would be most accurate to make your test exposures in complete units of stops and fractions of a stop that you determine. In other words do not work from accumulations of multiple exposures.
     
  3. Joe Lipka

    Joe Lipka Member

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    Just a simple observation and a question. If I tested printing times and the result was 7 three second exposures, why would I want to make the print another way?

    Or another way, if you make a test (experiment) and it gives you a result you want why would you change it when you make the full print?

    It does not make sense to test one way and print another.
     
  4. Jim Jones

    Jim Jones Subscriber

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    I haven't seen the Fred Picker video, but assume he suggests incrementing the exposure in 3 second steps. Even Ansel Adams suggested this in one of his books. This sounds like the equivalent of bracketing film exposure times in steps of 1/7, 2/7, 3/7, 4,7, etc. I don't understand that logic. Film and paper respond logrighmatically to exposure. The difference between 1/7 and 2/7 is a full stop. The difference between 6/7 and 7/7 is a small fraction of a stop.

    If I must make test strips from a problem negative, instead of fighting against the dictates of an electronic gismo, I use a clock that ticks fairly loudly every second. I start the exposure. After 2 seconds, I cover part of it. After another 2 seconds, another part. After another 4 seconds, another part, etc. This gives a sequence of 2, 4, 8, etc. Some may prefer a sequence of half stops, like 2, 2.8, 4, 5.6, 8, etc., or even 1/3 stops. Usually full stops gives me a good enough idea to interpolate the exposure and paper grade for the first full image test print. However, a cheap enlarging meter calibrated for flesh tones or the equivalent almost always suffices for the first full image test print.
     
  5. Bruce Osgood

    Bruce Osgood Membership Council Council

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  6. PeterB

    PeterB Subscriber

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    Crikey.

    I am kicking myself

    After all these years it finally dawned on me as to why most of the time my test strips didn't match the density of my prints !!!! I'm so stupid. I knew about the enlarger bulb warm up time, but never thought to factor it in.......

    Arghhhhh!

    Is there anyone else out there who has made or is still making this mistake, I need moral support by knowing you at least exist !
     
  7. Jim Noel

    Jim Noel Member

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    Donald,
    FYI f-stop printing times have been around muchl onger than you think. That is the way I learned to make test strips almost 70 years ago, and the method I teach today. It is just that no one had written about them until Gene Nocon came out with his timer and book.
    Jim
     
  8. Jim Jones

    Jim Jones Subscriber

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    Somewhere I, too, adapted that way of making test prints long ago, but not quite 70 years back. My 7th edition (1967) of the once ubiquitous Lootens on Photographic Enlarging & Print Quality by J. Ghislain Lootens uses exactly the same system. So do Neblette, Brehm, and Priest in their Elementary Photography, 2nd ed., of 1942. I can't find earlier citations in my little library without too much searching, but suspect logarithmic test strips date back about as far as developing out paper. Why Ansel Adams persisted in advising equal, not logarithmic, steps as late as 1968 in The Print is a mystery, but it certainly worked for him.
     
  9. RH Designs

    RH Designs Advertiser Advertiser

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    If you're using a colour or VC enlarger with a voltage stabiliser there's quite likely to be a "switch on delay" of up to half a second, and that can seriously affect the accuracy of exposures if you use the "cumulative" test strip method. With such enlargers for example four 5-sec exposures very definitely do not equate to one 20-sec exposure. Our timers can be set to compensate for this effect.
     
  10. Paul Howell

    Paul Howell Member

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    Thus it would be most accurate to make your test exposures in complete units of stops and fractions of a stop that you determine. In other words do not work from accumulations of multiple exposures.[/QUOTE]

    Donald is right, even the often maligned Kodak projection scale is designed for for a 1 mint exposure with times running from 2 to 60 seconds. I am under the impression that Ansal Adams set up controlled for blub warm up, I can get close with a tunston blub, but I still use the Kodak projection scale when using my cold light head.
     
  11. nlochner

    nlochner Member

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    I dont have any problems with making multiple 5 second exposures....


    Nlochner
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    Kodak used to recommend a single 60 second exposure with a cardboard covering the print for varying times. Thus the portion of the strip exposed for the full 60 seconds would be darkest and each of the sections would recieve 10 seconds less exposure.

    There are three reasons why you should not use multiple exposures.

    1. Light bulb on and off cycle is unpredictable. (timer error especially at short times)

    2. Light bulb on and off afterglow is uneven and startup changes as the cycles continue. The bulb filament is warmer each cycle and starts differently. Hue changes as well with heat.

    3. Less commonly known, some photo products don't respond evenly to multiple exposures. There is a kind of a reciprocity failure effect that is cumulative. This BTW, was a serious problem with earlier laser color papers as the overlapping scan lines got multiple exposures and the paper response was not the same as with regular white light exposure. That has now been corrected.

    PE
     
  13. fhovie

    fhovie Subscriber

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    I never use a strip - I make a test exposure - usually my first guess is within one stop - then I use the fstop chart to make the next - since film esposure is not linear - I do not use a linear exposure strip - fstop charts are the way to go. You could probably invent one - each stop is twice the exposure as the next - mine is broken down to 1/3 stop steps and goes several stops plus or minus for each exposure time out to about 30 seconds max. Past that - do it in your head - We use stops when exposing the negative - I never understood why we would stop using fstops when printing.
     
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  15. Edwardv

    Edwardv Member

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    Yes, me too. Now I got a headache. But would this be compensated by a Zone VI compensating timer?
     
  16. Dan Henderson

    Dan Henderson Member

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    f stop printing based on non-incremental test strips makes so much more sense to me now that I've adopted the methods. And the bear so much similarity to the way the aperture and shutter speeds work in the camera that they are (or should be) second nature to a photographer. I really don't understand why students are not taught that way from the beginning.
     
  17. Dan Henderson

    Dan Henderson Member

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    oh yeah, I also wanted to say that Ralph Lambert has excellent directions for a test strip printer in his even more excellent book, "Way Beyond Monochrome."
     
  18. Paul Howell

    Paul Howell Member

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    You can use a Kodak projection print scale, a pie shaped step wedge, place it over the print and set your timer for 60 seconds and read the print in seconds 2 to 48.
     
  19. nolindan

    nolindan Member

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    On the subject of multiple short exposures == one longer exposure and the accuracy of progressive test strips:

    With an incandescent enlarger, in my case a Beseler 45 and #212 enlarger bulb, several small exposures do indeed equal one long exposure.

    Using a grade 5 polycontrast filter ten 2-second exposures produce exactly the same shade of grey as one 20-second exposure. Ditto test strips of the sort where 1:1:2:4:8:16 ... second exposures are made as cardboard is used to progressively cover up the paper.

    If the total exposure time gets to be greater than 45 seconds then reciprocity failure will begin to factor in and short exposures won't sum
    in a linear fashion. At 45 seconds reciprocity failure is only just noticeable
    in normal printing.

    If you use a cold-light head this won't be the case unless you use a compensating timer [better known as an 'exposure integrator']. Even with a compensating timer errors will occur because the spectral sensitivity of the light sensor will not be the same as that of the paper: the spectrum of the light will change as the lamp warms up and a non-spectrally-matched sensor will not track the response of the paper.
     
  20. Mr_Rocketkiller

    Mr_Rocketkiller Member

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    Chalk one up for stupidity on me! My only excuse is I just started in a darkroom class about a month ago, and we were taught to use multiple exposures for test strips. Now I see why my test strips were always slightly off... :tongue:
     
  21. Ray Heath

    Ray Heath Member

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    beause Joe, 7x3sec is harder to control than 1x21sec, ie once you start the exposure you'll lose count of how many 3secs you've done

    it is correct, and easily demonstrable, that 7x3 is a lot shorter than 1x21, my procedure in such a situation is to redo the test strip as say 15+5+5, so if the 'correct' exposure is actually something like 18 the new test will soon prove it, then 1x18 is much more accurate

    don't worry about wasting paper on test strips, better to waste strips than waste whole sheets, do as many tests as you need to be confident of a good result

    a further consideration si not to change aperture to alter time, because when enlarging it's more important to have the lens stopped down to the middle of it's aperture range than it is to keep to a particular range of times
     
  22. Ray Heath

    Ray Heath Member

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    i would suggest there are problems of control and accuracy with any procedure, for istance in the above 60sec scenario, can the printer accurately cover the paper each 10 secs, what if one segment was actually 10.5 and the next was 9.5

    as for f stop printing, it sounds logical, but at some stage you have to decide on fractions of a stop, half a stop more than 20 is 28.3, not 30, but what if you did 30, who'd notice, 1.7 secs in 20 is not gonna make any appreciable density difference
     
  23. Don Grindstaff

    Don Grindstaff Member

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    I use a Kodak step wedge to get close and use an Ilford em-10 for the rest of the roll, Well worth the 20 dollars I paid for it you can easily change enlargement ratio and the adjust the f-stop to match the same metered area. I own a Color Star 2000 for color but for black and white the em-10 is all you need.
     
  24. jstraw

    jstraw Member

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    I became familiar with f-stop printing yesterday, via this thread. I'm doing the forehead-slap now too. Duh. I will be using this table:

    (One full stop separates each column.)

    5.0 seconds 10.0 seconds 20.0 seconds 40.0 seconds 80.0 seconds
    5.9 seconds 11.9 seconds 23.8 seconds 47.6 seconds 95.2 seconds
    7.1 seconds 14.1 seconds 28.2 seconds 56.4 seconds 112.8 seconds
    8.4 seconds 16.8 seconds 33.6 seconds 67.2 seconds 134.4 seconds


    And when I'm satisfied, I may invest in an f-stop timer.
     
  25. Nige

    Nige Subscriber

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    trouble with a table like that one is the steps are too great... bit like the Kodak exposure pie (although you can expose this for 30 secs and get closer segments). Ok for someone who has absolutely no idea of what exposure they'll need.

    I'm a seat of the pants, two step printer. I wouldn't recommend this to anyone! I look at the neg and proof sheet to guestimate a starting point then do a test strip concentrating on highlights at the starting point and 1 or 2 second segments depending on how confident I am of my reading of the neg. Occasionly I'll use a sequence like 3,1.5,1.5,3,3. Sometimes I'll check with the exposure meter (Colorstar 2000) to see I'm in the ballpark (it's pretty accurate but I like to run the test strip anyway). Once I've processed the test strip I pick the segment I like, set the timer and do another test print, usually with a bigger piece of paper. I may or may not alter contrast and get the altered time (when using my colour enlarger) I usually use the exposure meter to get the altered time as it seems to get that spot on. My 4x5 is a VCCE head so I just alter the filter dial. Might do another one of these, then use a full sheet of paper. While that's exposing I might decide to dodge and burn... on the fly. If I'm using RC paper I'll let the print air dry, fiber gets nuked in the microwave (although I'm not a big fan of this as I reckon the gloss level ends up different to air dried FB). I then decide if that is the final print I want or make further changes... something like that :smile:
     
  26. jstraw

    jstraw Member

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    1/4 stop steps are too big for you?