B & W control strips

Discussion in 'B&W: Film, Paper, Chemistry' started by lamda, Jun 4, 2009.

  1. lamda

    lamda Member

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    I am setting up my darkroom after a lapse of many years. I'm planning to test how everything works, and maybe try some film/developer combinations with no published times. I understand that pre-exposed control strips are available for Kodak TMAX 400 (and I'm not up on the subtle differences made over the last few years as production facilities were changed) and Ilford FP4+.

    I've downloaded some guides from the manufacturers with lots of details on how to use the strips, but one thing still puzzles me: what is the relative exposure of the various patches, so I could plot them on an incomplete H&D curve?

    (If anyone knows of a sweet deal on a densitometer, I'd like to hear about that too.)
     
  2. ic-racer

    ic-racer Member

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    If its a 21 step then they are usually 0.15 log d or one-half stop apart.
     
  3. Mike Wilde

    Mike Wilde Member

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    While have not tried this yet, I have theorized on making my own control strips.

    It was going to involve figuring an even lighting scene, and then with a macro lens set, and compensating exposure for any bellows factor, expose 3 sucessive frames of 35mm film while placing different sections of a reflective step tablet of the sort found in Kodak old data guides. Then I would have a white, a black, and a grey exposure that were made of a paper chip printed to a given denisty known numbers of half stops apart.

    The idea could be expanded to take a picture of a constant intesity light source against a transluscent screen, and then meter to get middle grey, and open up the lens to meter white properly, and then close the lens aperture down to get a sucession of exposures a half stop apart.

    The 'home made test strip' film should be developed with the rest of the tank full of a section of film shot 'normally' or all middle grey, I suppose. The idea here is that you don't want all of the developer acting just on a few frames to set your time, and then when you develop a full roll, find that it poops out a bit faster when confronted with 36 exposures, say, rather than just 2 or 3.

    If you don't have a denitometer, then there is the possibility of using an enlarger as a light source (standardize the aperture, lens, head height, and no dichroic filtration) and then use a camera or light meter to measure the light falling on a white card placed on the base board lit only by the enlarger's output. If using a camera, or light meter, work up a jig so that it 'sees' the same thing every reading. Note the meter reading for the black, white, and any greys, and work out what the exposure product is, take it's log, and plot it.

    Not the easiest thing to do, but where circumstance demands, and the proper tool is not at hand, improvise.

    The other option to judging developed test film sections density is to buy a 1/3 stop (0.10 step) transmission step wedge, and use it to visually compare your greys and white and black to it's known denities while looking though both against an evenly lit translucent surface masked to only show you the step wedge one step at a time, and your test speciment immediaty adjacent to the step wedge window. You may be surprised with a calibrated reference how well your eye is able to match densities.
     
  4. ic-racer

    ic-racer Member

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    I made curves like you described and it does work OK. It is very tedious to make the 21 exposures. One mistake in matching up the appropriate the frame number and you are hosed (especially if the first 4 exposures show film-base-only) . However, there are lots of sensitometers for sale out there. Any with "white light" are good but I suspect the popular green-blue ones will probably work just fine for making control strips. One of these days I'm going to put a green filter in the filter drawer of the WEJEX and see if it corrupts its ability to make a control strip (I think not).
     
    Last edited by a moderator: Jun 5, 2009
  5. ic-racer

    ic-racer Member

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    FYI: here is a typical sensitometer for making control strips. It is simple but precise in construction. There is not much in the box except an incandescent bulb, diffuser and a stepper-motor shutter. (its all AC). You may be able to see the step wedge in the window. The enclosing box is high to provide enough distance from the light to the film to minimize 'cosine falloff.'

    [​IMG]
     
  6. Kirk Keyes

    Kirk Keyes Member

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    I use my enlarger to make B&W control strips. I contact print a Stouffer 21 step wedge onto film. I filter the enlarger light to correct it to daylight, and then I use my Minolta Flashmeter IV with a flat diffuser to measure the lux. I then use a digital timer to turn the enlarger on for 1 second. A setup like this is all you should need to make your own control strips.

    Densitometers - The Photographers Formulary in Montana carries B&W densitometers that are from the medical field and have been fully reconditioned. Email them and ask - I think they were in the $400 or so range. They do both reflected and transmitted, I believe.
     
  7. ic-racer

    ic-racer Member

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    Thats nice. Then you can be verify you have the same enlarger height, lens, focus, f-stop and baseboard position etc.
     
  8. Kirk Keyes

    Kirk Keyes Member

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    Yeah, the enlarger always is set to the same height, the lens is focused on the baseboard, and printing frame is put in the same place and the area that is occupied by the frame is measured with the meter to verify that the lighting is even and the amount of light is recorded. (The thickness of the printing frame is about the same as the meter.) I can use differing f/stops (lux amounts) for different speed films.