reading negative density without a ...

Discussion in 'Exposure Discussion' started by ilfordrapid, Sep 27, 2005.

  1. ilfordrapid

    ilfordrapid Member

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    Is there a way to read negative density without a densitometer. For rating film speed, and development times. I suspect that a spot meter and enlarger will come into play here. I have a diffusion enlarger and a spot meter, but it does not accept attachments.
     
  2. L Gebhardt

    L Gebhardt Subscriber

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    The book Beyond the Zone System has a simple looking setup that uses a spot meter and a light table. I haven't tried it, but think this would work fine. and give you about 1/3 of a stop accuracy. Some darkroom exposure meters, like the RH Designs Analyser, also can be used as densitometers.

    Used densitometers are going for a not much money these days on ebay, so you may just want to save some trouble and get one.
     
  3. Loose Gravel

    Loose Gravel Member

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    I understand this can be done with a film scanner. If not, go with one from ebay. I got a nice one for $30. It was sold as broken, but it only needed a fuse.
     
  4. dancqu

    dancqu Member

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    Ilford's EM-10 spot enlarging meter can be used.
    Calibrate against a step wedge. Dan
     
  5. modafoto

    modafoto Subscriber

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    Any info on this approach? I own a nice film scanner and would love to be able to use it as a densitometer, too. Any special software?
     
  6. Lee L

    Lee L Member

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    I've had very usable results using a Minolta Spotmeter M (that reads to 1/10 stop) and a diffused lightbox. I've also had good results using a diffused light source (a 5000K flourescent bulb in a reflector) and the film placed over the aperture of a Gossen enlarging attachment on a Luna Pro F.

    I don't know the procedure using a scanner, but I'd presume you need to start with a decent step wedge and software that allows you to set and maintain specific manual settings, i.e. no autocorrection of exposure, gamma, etc.

    Lee
     
  7. Tach

    Tach Member

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    FWIW, I use a cheap CdS cell and a digital multimeter. Details in this thread:
    Homebrewed densitometer

    Accuracy against a calibrated transmission tablet from Stouffer is good, and overkill for film development.
     
  8. seadrive

    seadrive Member

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    I've been using my Adorama spot meter with one of those cheap, battery-operated lights that you put on a wall in your closet, and push the dome to turn on. If you're careful, you can read density differences down to about a 1/6 of a stop (is it on 10 1/3, 10 2/3, or between the two?), which is plenty fine enough for basic film exposure ratings and development time tests.

    You need a piece of film that has been developed with no exposure, to give you your film base + fog reading. Then, it's just a matter of measuring the increasing density of sheets of film rated at different EI's, compared to your FB+F base.

    Seems to work well...
     
  9. Flotsam

    Flotsam Member

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    I seem to remember that there is an article on APUG that covers this.
     
  10. dancqu

    dancqu Member

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    The EM-10's non linearity and 0 to 100 dial are it's
    short comings. It does present a Very tight spot
    when used on the baseboard.

    To calibrate use a 21 step step wedge. To read,
    interpolate. Use a middle range as most negatives
    fall within a density range of less than 1.5.

    BTW, off eBay I purchased a Tobias TB+ in near
    new condition and with instructions and all the
    extras for under $80. Dan
     
  11. modafoto

    modafoto Subscriber

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    I tried to find it...I couldn't :sad:
     
  12. JHannon

    JHannon Member

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  13. modafoto

    modafoto Subscriber

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  14. Photographica

    Photographica Member

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    I've had the notion that a color analyzer and something to calibrate with (step tablet) would make a good densitometry arrangement. The idea occurred when at an auction recently I witnessed 3 analyzers sold as a lot for $5.00
     
  15. Dan Henderson

    Dan Henderson Member

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    The latest edition of Photo Techniques magazine has an article describing how to use a film scanner to read negative densities. You also need a transmission step wedge and a program that you can download free from the internet. I just read it and haven't had time to try it yet, but will as soon as I can get my hands on a step wedge.
     
  16. smieglitz

    smieglitz Subscriber

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    The cheapest way to do this is to pick up a Stouffer 21-step transmission density tablet for about $9 from a graphic arts supplier or Bostick & Sullivan. Surround the thing with black opaque paper and place that over a piece of blank film (unexposed but developed) of the type you're testing. Take it to a light box and along with your test negative(s) and a couple 3x5 cards with paper-punched holes in them, and visually compare the density on your test negative to the steps on the tablet.

    This is remarkably accurate. The steps of the tablet increase in an increment of 0.15 and usually have a base density of for step 1 of about 0.05. By placing the tablet over a piece of blank film having only fbf density, you can read net densities very easily with this method.

    Another way to achieve the density comparison inexpensively is to purchase a 0.10 wratten neutral density filter and use it on a blank piece of film to compare visually to a test film. This is less versatile however since it will only allow you to identify the speed point density of 0.10 above fbf.

    Henry Horenstein's basic photography text goes over the latter test and Sullivan & Weese's New Platinum Print book outlines the former. IIRC, I believe S&W originally got the idea from an early issue of The World Journal of Post-Factory Photography.

    Joe