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  1. #1
    kwmullet's Avatar
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    spot meter as a REFLECTION densitometer on the cheap

    There's a good handful of descriptions at various places on the net as to how to use a spot meter as a substitute for a transmission densitometer in measuring negatives. I've looked all over the place and haven't yet found any descriptions of a good method for using a spot meter as a cheap REFLECTION densitometer for measuring prints. I tried measuring contact prints of a step wedge, but as the angle of measurement changed as I measured different spots in the same step, the EV value changed.

    Has anyone come up with a good method for doing reflective densitometry with a spot meter?

    scratching my head...

    -KwM-

  2. #2
    Bob F.'s Avatar
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    Quote Originally Posted by kwmullet
    There's a good handful of descriptions at various places on the net as to how to use a spot meter as a substitute for a transmission densitometer in measuring negatives. I've looked all over the place and haven't yet found any descriptions of a good method for using a spot meter as a cheap REFLECTION densitometer for measuring prints. I tried measuring contact prints of a step wedge, but as the angle of measurement changed as I measured different spots in the same step, the EV value changed.

    Has anyone come up with a good method for doing reflective densitometry with a spot meter?

    scratching my head...

    -KwM-
    Not tried it, but making a foamcore or thick card (or plywood if you want something more permanent) holder for the meter so it is always at the same angle should do it. Keep it on the holder with a couple of elastic bands. As long as the light source is constant, with the holder keeping the meter at the same angle, it should work. The BTZS book shows a similar, but more substantial idea.

    Cheers, Bob.

  3. #3

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    Quote Originally Posted by kwmullet
    Has anyone come up with a good method for doing reflective densitometry with a spot meter?
    I took a class 10+ years ago that was based on Davis's BTZS principles. All the sensitometry work was performed using a Pentax analog spot meter. The meter was mounted in a hand fabricated plastic cradle. The cradle also held a closeup filter so that step wedge sections were in focus when you read them. A work lamp provided the illumination and the collar that held the lens of the meter had a rotating section that either opened or blocked a port that allowed for reflected metering. You then converted EV to log D by referencing a chart. I'm pretty sure that all this was modeled after the directions in the workbook that came with the first edition of BTZS.
    Some options:
    1)find a copy of the BTZS workbook which I'm pretty sure is out of print, (maybe try on the BTZS board)
    2)failing that I'm pretty sure that the doohicky that I'm describing still exists and I could probably get you a photo
    3)buy a used xrite reflection desitometer from a print shop that is going out of business or going digital. This was my option. The densitometer was very cheap, less of a pain to use and required no construction labor. YMMV.
    Good luck.

  4. #4

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    I don't think that a spot meter will give the degree of precision that I would want to determine reflection density. For instance, the Pentax digital that I have will only get as near as 1/3 stop. If I missed the reflection density by 1/3 stop at the low value and missed it by 1/3 stop at the highlight end then this would translate to .20 in exposure scale variance under the best of circumstances.

    To take this a step further, I think that this best case scenario is unrealistically ambitious.

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    Phil Davis Beyond the Zone System (my copy is 4th edition) has an Appendix section on building a reflection/transmission densitometer with a Pentax spot meter. The working drawings are quite detailed.
    van Huyck Photo
    "Progress is only a direction, and it's often the wrong direction"

  6. #6
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    Spot meters have been known to suffer from flare, which will tend to "smear" the measurements. This is more likely the cause of variation of readins along a step of constant reflectivity than the angle, especially if the step is on a diffusely reflecting material. Some years ago there was an article in Photo Techniques that showed that flare, but I can't remember when, or who wrote it.
    Gadget Gainer

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    Quote Originally Posted by pelerin
    find a copy of the BTZS workbook which I'm pretty sure is out of print
    No it's not.
    The latest edition of Beyond The Zone System can still be ordered at www.focalpress.com. "Beyond the Zone System (4th Edition), Phil Davis, £37.99, ISBN 0-240-80343-4".
    Wilbert
    http://www.photovergne.com
    Cours photo en Auvergne

  8. #8

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    Our own Dr Bob wrote a very good article on using a spotmeter to measure density.

    Here is the link: Spotmeter Article

    I was getting usable results using a spotmeter with a light table. I used a series of adapters on the meter to get it to fit on a reverse mounted Pentax 80mm lens. I added a rear lens protector then drilled a hole in the center of the lens protector. The reverse mounted lens was to get it to focus closely.

    I hope it helps,
    Regards,
    John

  9. #9

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    How about using a different piece of hardware for densitometry--a scanner? I have not done anything like formal testing, but I use SilverFast software when scanning prints. If you use the straight line algorithm when scanning, with no manipulation, you should get an accurate representation of your print. SilverFast SE 6.0.2 has a densitometer. I have played with this, and it seems useful. Does anyone have experience using a scanner to formally analyze your dried-down prints?

  10. #10
    kwmullet's Avatar
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    Quote Originally Posted by JHannon
    Our own Dr Bob wrote a very good article on using a spotmeter to measure density.

    Here is the link: Spotmeter Article [...]
    John,

    Great article recommendation. I'll certainly go through it in more detail when measuring negs, but in this particular instance, I'm looking for a way to do REFLECTION densitometry of a print, not TRANSMISSION densitometry of a negative.

    -KwM-

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