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Thread: Calibration vs. Consistency

  1. #11

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    Re: Calibration vs. Consistency

    Calibration is important if more than one person uses this meter or if you use more than one meter. I use a spot meter and an incident (flash) meter, both Sekonic. Both have their own purpose, but it is good to have one as backup for the other. Then I want to be sure to get accurate readings at the same film speed setting.

    Michael

  2. #12
    Drew Wiley
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    Re: Calibration vs. Consistency

    These meters are not only calibrated to an objective standard, but to internal linearity as well. They periodically need to be tested and recalibrated. You might just
    get accustomed to a certain reading error; but if the linearity is appreciably off, so too is your Zone System assumptions or whatever. My custom was to keep a
    brand new Pentax digital spotmeter in the lab which was never used for anything other than checking my user ones. Once one of these showed a discrepancy with
    any of the others, over their entire range, it was time to send them in for recalibration, which averaged about once a decade. Eventually in the not too distant
    future I'll have to enlist that spare meter into regular duty, cause one of my old ones is getting pretty rickety, even though it still reads true. Or maybe I'll find a deal on another new one - but ya already know, these things don't go cheaply these days. Even when I also used a Minolta Spotmeter F in the studio, it exactly
    matched the Pentax meters over the full range. I found Pentax more convenient to use in general. But at least this demonstrated that these two brands were
    originally calibrated to the same strict standard.

  3. #13

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    Re: Calibration vs. Consistency

    Drew, that's a good point about "internal linearity." I do occasionally check my three meters--Gossen Luna Pro F, Minolta Flashmeter V, and the Pentax--against each other, both in absolute measurement and in relative terms. Not very scientific, I know, but if all three agree within half a stop or so (which they usually do) I figure I'm doing OK.

    Calibration also opens up a huge rabbit hole in my case because so many of my shutters are not functioning at 100%. Even if my meters were magically made perfectly accurate, I would then feed those readings into a given shutter that might be off 20-30% at certain speeds (not to mention my use of the "Galli shutter" which introduces human error into the equation). If I were to have my meters calibrated I would also need to have my shutters cleaned and tested, and that seems a fool's errand with all of the old Compurs and Ilexes I have. If I shot transparencies I might be singing a different tune, but LF B&W has a generous amount of exposure latitude built-in, or at least enough to smooth out the ripples caused by my uncalibrated gear.

    J.

  4. #14
    Drew Wiley
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    Re: Calibration vs. Consistency

    I keep a shutter tester on hand in the lab too. But my own habits were standardized around transparencies and I've kinda stuck with it. I find that kind of precision
    very useful when dealing with Ektar too, which is a bit more finicky than most color neg films. It's also helpful when trying to squeeze in the bottom rung of shadow
    detail using steep-toed films, which I often find myself doing, given the extreme contrasts of lighting I often encounter in the mtns, desert, or even in the redwoods
    when the sun comes out. But black and white work is a lot more forgiving in general. I will admit that.

  5. #15
    Resident Heretic Bruce Watson's Avatar
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    Re: Calibration vs. Consistency

    Quote Originally Posted by jcoldslabs View Post
    Since I use the same meter for all my exposures and have determined my own exposure indexes and development times for various films based on this meter's readings, what good would getting it calibrated do?
    Calibrating your meter would probably be of little value to you, and it would necessitate retesting for your personal EI and development times again.

    What you've found is the difference between accuracy and precision. They aren't interchangeable concepts as you've shown.

    This is why I run my Jobo at 19.4 degrees. Because it needs calibrating; it's not accurate. But it's quite precise. Every batch of film I run comes out just like the last batch. Since it's not really broken...

    Bruce Watson

  6. #16
    Drew Wiley
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    Re: Calibration vs. Consistency

    Why calibrate, Bruce? Because if it has already started drifting from its original setting, it's going to gradually keep drifting. If it ever needs actual repair, it will have
    to recalibrated anyway. And if someone happens to need a spare meter, it's important to match them. And as meters drift, they might not do it symmetrically. It
    might remain accurate at one point and not somewhere else in the overall range. One damn box of color sheet film can cost more than the price of recalibrating a
    Pentax meter.

  7. #17
    Kirk Gittings's Avatar
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    Re: Calibration vs. Consistency

    If you are going to recalibrate make sure you do a reading off of a consistently lit subject before you send it in so you can compare it when it comes back. Then your exp/dev processes may just need a film ASA adjustment in exposure to keep rolling. I have it done every few years whether I have noticed a problem or not.
    Thanks,
    Kirk

    at age 73:
    "The woods are lovely, dark and deep,
    But I have promises to keep,
    And miles to go before I sleep,
    And miles to go before I sleep"

  8. #18

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    Re: Calibration vs. Consistency

    I had a very similar conversation with someone I bought a lens off. When I received it the times were off, you could tell without having it tested. I sent an email to him complaining he did not mention this in his listing. He wrote back and said that each photographer gets to know their lens initmately and adjusts exposure settings accordingly to get the desired result. This is the same theory to your point about your light meter.

    I minimise the use of my light meter, often taking just one reading then putting it away and tend to be guided intuitively from that point based on what I know from experience. This was recommended by F.C.Tilney, a fine arts historian and pictorialist photographer from the early 20th century.

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