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Thread: How to Develop Characteristic Curves in Large Format...Cheaply

  1. #11

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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    Quote Originally Posted by sperdynamite View Post
    I'm looking for a Densitometer
    While you dont have it...

    just scan (16 bits per channel) an stouffer T2115 transmission wedge alongside with your negative, at the same time with all image enhancing disabled, then in Ps just compare the gray values in a spot in the gegative with the patches in the scanned wedge.

    perhaps not as convenient than a densitometer, but perfectly accurate. I've a densitometer but I use that way.

  2. #12
    Drew Wiley
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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    Poor man's densitometer : Take a sheet of black cardboard and an ordinary hole punch. Punch the holes a few inches apart. Place your step wedge atop a light box adjacent to the sheet film neg you're trying to measure, then the black cardboard atop both. One hole should be over the part of the negative you're trying to read, and then shift your step wedge until the patch on it which most closely visually matches the area on your neg matches. It's called visual densitometry, and is quite adequate for basic purposes or elementary plotting, including the Zone System. For high-quality plotting, get a real b&w transmission densitometer and appropriate graphing sheets, or else a program that accepts your reading and plots the curve for you.

  3. #13
    ic-racer's Avatar
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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    In graduate school, before I obtained a real densitometer, I placed my samples between my spot meter and a light bulb to make the H&D curves. When I got a 'real' densitometer, the curves I made were pretty much the same.

  4. #14
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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    Quote Originally Posted by ic-racer View Post
    In graduate school, before I obtained a real densitometer, I placed my samples between my spot meter and a light bulb to make the H&D curves. When I got a 'real' densitometer, the curves I made were pretty much the same.
    Phil Davis's BTZS book, or at least the third edition which I have, has an appendix with some guidance on using a spot meter as a makeshift densitometer.

  5. #15

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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    Also... On a light table, we may check exposure with the spot meter of a dslr in a point of the negative, and later finding the matching patch in the Stouffer, also with the spot meter.

  6. #16

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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    The worst thing to no information is incorrect information. Use a densitometer!

  7. #17

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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    Quote Originally Posted by Luis-F-S View Post
    The worst thing to no information is incorrect information. Use a densitometer!
    This is very good advice, no doubt.

    Anyway let me point that the greatest errors sometimes come from the best instruments.

    Today we can access used great densitometers at low price, I got my very good one for $25, but the important thing both in new and used gear is checking accuracy.

    Fortunately we may use calibrated wedges that allow to check used and new gear, and very pro or DIY made devices.

    As always in any kind of lab, it is important to check accuracy in instruments because a reading is never perfect, and even a very good instrument may end in a pitfall because some dirt is in the sensor.

    A Calibrated wedge (or even a regular one) it is what in fact what we need to know what we are doing.

  8. #18

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    Re: How to Develop Characteristic Curves in Large Format...Cheaply

    I thought I'd pitch my book... I think I've sold one copy. Oh yeah I didn't really sell it. One day a Photrio member 'peoplemerge' came by my local coffee shop and I gave it to him along with a GE light meter. Yes you can make a densitometer out of a GE light meter.

    http://beefalobill.com/imgs/20150812...dAttention.pdf


    Here's an excerpt from the book relevant to this thread... echo's of Pere Casal's advice... buy a T2115 for the price of one sheet of film. If you like get the calibrated T2115C for about the price of three sheets of film.


    Recommended: Stouffer Step Wedge T2115
    ( http://www.stouffer.net/TransPage.htm )
    You can set this scale on top of a piece of film, cover it with a piece of glass, as for contact printing, and
    expose under an enlarger. Although this isn’t highly accurate, it is easy to setup and will be much better
    than most other test methods. There are two important flaws in the test: reciprocity law failure may
    occur due to a few seconds exposure and the light source of the enlarger is different than the spectrum
    of light you would probably use when taking pictures. The advantages of contact printing outweighs
    the significance of these flaws.

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