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  1. #21

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    To test for linearity ideally you need a single light source of known colour temperature, which is then attenuated with neutral density. And of course it must uniformly fill the field of view.

  2. #22
    David Lyga's Avatar
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    I guess we'll have to leave it at the 'pragmatic shortcoming', Michael, as I am hardly that sophisticated. But, you are most likely correct and maybe some will delve further into this. - David Lyga

  3. #23

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    I made comparison most of the time. I found many of the old timers camera meter response are non linear.
    I use the dichroic color head as light source. Dialing in equal amount of filters made neutral density. Monitoring the filtration tightly with a color analyzer keeps the color balance from shifting when adjusting the filters. Use a good reference spot met the to check light level.

  4. #24

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    Quote Originally Posted by David Lyga View Post
    I guess we'll have to leave it at the 'pragmatic shortcoming', Michael, as I am hardly that sophisticated. But, you are most likely correct and maybe some will delve further into this. - David Lyga
    Get Richard Henry's book if you are interested in this. However he was testing 1 degree spot meters so in the end it probably isn't directly applicable, although it still makes for interesting learning.

  5. #25
    fotch's Avatar
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    There is an old saying, something like a person with two watches (clocks) will never know the exact time. Just saying......
    Items for sale or trade at www.Camera35.com

  6. #26
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    "If a man has a clock he knows what the time is, if he has several he's not sure". The quickest ways I know of a photographer to drive himself crazy is to compare light meters, and thermometers.
    Ben

  7. #27

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    Well, thermometers are not as bad. Assuming you invest $100 in a certified/calibrated thermometer you can use it as a reference source. With light meters, there are many variables and many different ways in which they can give different readings. Everything from k-factor and other calibration issues (spectrum), to linearity, to measurement field, to optics (flare). Meters are a horribly complicated mess of variables. Fortunately our films etc. provide plenty of latitude, and "errors" may tend to offset eachother.

  8. #28
    RalphLambrecht's Avatar
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    in photographythere are countless varibles and everything depends on everything else.it is a real miacle we get any pictures at all.it is a wonderfultechnology.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  9. #29

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    Quote Originally Posted by fotch View Post
    There is an old saying, something like a person with two watches (clocks) will never know the exact time. Just saying......
    That saying is wrong. No timepiece keeps a perfect rate, therefore nobody knows exactly what time it is. The closest the average person can get is to listen via shortwave to the WWV time signal, but you'd better apply a correction to allow for the time it takes for the radio signal to propogate from the transmitter to your reciever, and then another correction for the distance between the radio's speaker and your ear (unless you're watching the signal on a 'scope).
    A watch or other timepiece that has stopped is at least correct twice per day (assuming it has a 12hr dial, once per day if a 24hr dial) but you'll never know precisely when.

  10. #30

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    I keep several matched meters. When one of them reads differently anywhere over the entire scale, I sent it in to Quality Light Metric for
    recalibration (about $100, but only needs to be done about once every 10 yrs).

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