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  1. #21

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    Roger! As far as I know CdS has a spectral response fairly close to that of the human eye. It's most sensitive to green light. Sillicon however is extremely sensitive to infra red as well as red light. When used in an exposure meter a blue filter has to be used to correct this problem and thus the term Sillicon Blue Cell.

  2. #22
    Roger Cole's Avatar
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    You're right. My mistake.

    I should have said is that CdS cells are much less linear in their response WRT intensity, making meter design more difficult.

  3. #23

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    Yes in that case it's true. Besides the design of most CdS based meter do not use a logarithmic amplifier and thus even if the response of the CdS cell is fairly linear its output isn't linear to the EV readout. I have done some experiment by copying the design of some CdS meter and found that without such an amplifier (a circuit that only has resistors, a power source and a galvanometer) can be made linear to a range of about 7 or 8 stops. And then I would have to put neutral density in front of the cell to switch to higher range.

  4. #24

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    Quote Originally Posted by Roger Cole View Post
    My mistake.
    I've never seen that before. This is so shocking that I think I'll write it down in my diary!

  5. #25

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    Quote Originally Posted by Roger Cole View Post
    You're right. My mistake.

    I should have said is that CdS cells are much less linear in their response WRT intensity, making meter design more difficult.
    Selenium, or more properly iron selenide, cells are photovoltaic cells. They actually generate an EMF when light falls on them. All the other 'cells' you mention are photoresistive, that is the rseistance changes according to the intensity of illumination.
    The Gossen LunaPro (LunaSix, LunaSix 3) was indeed a CDS meter, and the battery problem isn't a problem if you use #675 hearing aid cells with 3 of the 4 airholes blocked for longer life (up to a year).

  6. #26
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    Quote Originally Posted by Roger Cole View Post
    Totally agree but that needn't mean new or modern. I like my Luna Pro SBC too - same meter with an updated cell and uses an available-anywhere 9v battery.
    I have a Gossen Profisix (Luna Pro SBC) I retired to my sock draw about two years ago because modern digital light meters also have Silicon Blue Cells, often 2 and are much quicker and simpler to operate, can read the light to 1/10th of a stop, are much less cumbersome, and more versatile can read a mixture of ambient light and flash and balance them, have a built in 1º spot meter and remember up to 9 meter readings and average them if required. The Lunapro S.B.C was a cutting edge meter more than twenty years ago but in my humble opinion the modern digital meters are much better and my Kenko KFM 2100 runs off a single AA battery which is even more common than a 9Volt PP3.
    Ben

  7. #27
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    Suit yourself - I like mine. And there's something vaguely heretical about using a digital meter with my Yashocamat anyway.

    And for the whatever number time I certainly KNOW that selenium generates a current on light exposure and doesn't need batteries. Anyone who ever tinkered with electronics knows that. And anyone who didn't would have still learned it earlier in this thread.
    Last edited by Roger Cole; 08-11-2012 at 10:56 AM. Click to view previous post history.

  8. #28
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    Quote Originally Posted by Roger Cole View Post
    Suit yourself - I like mine. And there's something vaguely heretical about using a digital meter with my Yashocamat anyway.

    And for the whatever number time I certainly KNOW that selenium generates a current on light exposure and doesn't need batteries. Anyone who ever tinkered with electronics knows that. And anyone who didn't would have still learned it earlier in this thread.
    Even at the age of seventy three I don't understand why some people in the 21st century have such a adversity to equipment that is battery dependant carrying spare batteries in your bag isn't heavy or difficult and speaking personally I've had only two new Lithium batteries in my Canon A1 in over twenty years and only one AA battery in nearly three years I have owned my digital light meter.
    Ben

  9. #29

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    Quote Originally Posted by benjiboy View Post
    Even at the age of seventy three I don't understand why some people in the 21st century have such a adversity to equipment that is battery dependant carrying spare batteries in your bag isn't heavy or difficult and speaking personally I've had only two new Lithium batteries in my Canon A1 in over twenty years and only one AA battery in nearly three years I have owned my digital light meter.
    Oh, there's just something nice about having to depend only upon the sun for power. One less thing to think of.

  10. #30
    Leigh B's Avatar
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    Quote Originally Posted by benjiboy View Post
    ... I don't understand why some people in the 21st century have such a adversity to ...
    Why should you?

    People are stating their opinions and preferences.

    They do not invite nor require your evaluation.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

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