How to fix a handheld light meter?

Discussion in 'Collector's Corner' started by Aquarium Dreams, Jul 17, 2007.

  1. Aquarium Dreams

    Aquarium Dreams TPF Noob!

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    I have a beautiful Bertram light meter (reflective), but unfortunately it doesn't work. The needle just bounces between 0 and 2. I was thinking about opening it up and poking around inside, but I don't know anything about how the guts work in a light meter. Does anyone have any experience with this, or know of a link that points in the right direction? I'd rather do it myself than send it out, if at all possible. Thanks.
     
  2. Mitica100

    Mitica100 Moderator Staff Member Supporting Member

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    AD, what model of Bertram is your lightmeter? Is it a Selenium cell based or does it take a battery? Can you post a picture?

    I know cameras but not lightmeters. My opinion, before knowing what model you have and all that, is that you might need to get a new one. I've been very happy with Sekonics and Minoltas.
     
  3. Hertz van Rental

    Hertz van Rental TPF Noob!

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    I think it is most probably a Selenium cell meter.
    These things consist of a Selenium cell, shunt resistor and a galvanometer.
    The cell generates electricity in proportion to the amount of light falling on it. This voltage is then measured by the galvanometer to give a calibrated reading.
    Most have a variable resistor as well which is used for calibration.
    There is not much that can go wrong with one of these. The most probable are:
    Damaged wiring: these could be caused by a 'dry' joint, corrosion or mechanical stress. Usually stops the thing working altogether.
    Calibration issues: if you get a reading that changes with light intensity but not accurately then the calibration may have gone. Adjust using the VR and another light meter.
    Most common: Selenium cell failure. These only have a limited life and this is dictated by the amount of exposure to light. The more the meter is used the quicker it will fail.
    Indications are repeated innacuracy despite calibration followed by decreasing response to light. Then 'death'.
    You can get cells replaced but it is not cheap. You can do it yourself but it's not easy.
    Selenium wafers have to be cut to the correct size and thickness so they will fit - if you can find somewhere to do it.
     
  4. Aquarium Dreams

    Aquarium Dreams TPF Noob!

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    It's the Chronos model and looks pretty similar to this one:

    [​IMG]

    I umm... dismembered it, and yes, it has a thin selenium cell in it. I read that acetone sometimes revives them, but that didn't work. It looks like a shop in the UK called Megatron customs cuts selenium cells, but like Hertz says, it's not cheap. Well, it's a pretty paper weight, anyway. Next time I'll try a Sekonic. Thanks guys.
     
  5. dustyroads

    dustyroads TPF Noob!

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    I have never seen a red Bertram Chronos Light Meter. It looks very nice. Did you paint it yourself? Do you want to sell it? Thank you for your time.
    Regards
    dustyroads
    silver-lobo@live.com
     

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