How does this lightmeter work?

Discussion in 'Lighting' started by openbinary, Jun 7, 2012.

  1. openbinary

    openbinary Member

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    I recently received a very old light meter and I have no idea how it works. It took me a while to find out the make/model but I can't seem to find anywhere instructions on how I can use it. APUG is my last hope :smile:

    The light meter is called Exposimet and it was made by the Czech company Metra. Here's a picture of it:
    metra.jpg

    I've never used a light meter before but I assume that based on the input of 2 values and you find out the third e.g. you set ISO(marked DIN on the device) and Aperture and you find out the exposure time.

    The device is completely solid and the only moveable parts are the exterior ring (which contains the ISO values and Aperture as well as a series of numbers from 3 to 15) and the needle of the meter. There's a red arrow on the body pointing to the ring which indicates either a result or an input value.

    Does anyone have any idea on how to correlate the values? Any help is greatly appreciated.

    Thanks!
     
  2. Mike Wilde

    Mike Wilde Member

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    The meter reads EV's - a set of equivalent combinations of shutter speed and aperture all equate to one EV for a given film speed.

    Old Rolliflexes/Rolicords used this as an exposure setting means, I think - you lock the shutter and aperture setting rings together at a given EV, then as you move the shutter faster the aperute proceeds to also open wider, and vice versa.

    Fred Parker's 'ultimate exposure computer ' - look on the web- explains light and EV's well, if in a bit of a long winded maner.

    The meter you have is likely powered by a selenium cell, which can 'poop out' over the decades. Check that the results are reasonable before you start to rely on it.
     
  3. Jim Noel

    Jim Noel Member

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    ISO and DIN are not the same. Look up a chart which compares light value systems.
     
  4. Jim Noel

    Jim Noel Member

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  5. Bill Burk

    Bill Burk Subscriber

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    That's a really odd dial. Looks like you have to align the DIN to the needle every time. Then you get EV on the red triangle - and combinations of f/stop-shutter speed below.

    May be possible to rotate dial to place DIN across from the shutter speed you want to use, then read f/stop directly from the needle.
     
  6. Diapositivo

    Diapositivo Subscriber

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    Try to go outside in the sun. Let the sun at your back, point the light meter in front of you. That should read around 1/125@f/11 or 1/125@f/16 on a sunny day, with DIN 21.

    PROBABLY you must align the DIN number with the needle (or the "stripe" which the needle indicates). So for the case in your picture, you should turn the crown until (let's say you have a DIN 21° film, corresponding normally to ISO 100) the 21 is aligned to the white stripe indicated by the needle.
    This will give you an exposure index (the red arrow on the right pointing to a red figure) and a series of exposure couples on the lower part of the ring.

    So if you go outside on a sunny day, and you have a DIN 21° film, and you align the 21 with the stripe indicated by the needle, you should see e.g. EV 14* and the following exposure couples:
    30/22
    60/16
    125/11
    250/8
    500/5.6
    1000/4

    Fabrizio

    * Edited from the original EV 15. The exposure couples above correspond to EV 14 at 21° DIN.
     
    Last edited by a moderator: Jun 7, 2012
  7. Bertil

    Bertil Subscriber

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    Normally meters of this kind that I have used are such that the EV figures (the reds 3-15) correspond to the white/black stripes, such that if the needle points to a particular stripe you can follow the strip up to the corresponding EV number; which EV number you get for a particular needle reading will depend on the DIN you have set on the meter, and every EV number correspond to specific speed/aperture combinations; this is the normal.

    These scales look a little bit odd, but should as Bill says, work by correlating the DIN on your film to a stripe which the needle points to, and than read the EV number, or the speed/f-stop at the red triangle.

    A little bit confused by Fabrizio's EV 15 list. Hasselblads Zeiss lenses all have the EV scale and according to all these lenses EV 15 corresponds to the following list:
    EV 15:
    15/f:45
    30/f:32
    60/f:22
    125/f:16
    250/f:11
    500/f:8

    If the meter works properly and you point it to a normal contrast view you should get something like 1/125@f/11 or 1/125@f/16 on a sunny day, with DIN 21, as Fabrizio indicates. But that would be EV 14 or EV 15.
    /Bertil
     
  8. Diapositivo

    Diapositivo Subscriber

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    Correct, the exposure couples I gave correspond to EV 14, I'll edit the text.
     
  9. openbinary

    openbinary Member

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    Ah! So it was the EV that I was missing. By setting this value I can get the other correct readings and they correspond to the values you guys wrote in the above posts. Good thing I don't have to know the EV table values by heart :smile:

    Mike Wilde was right though, the meter seems to have lost some of its juice; the exposure time seems to be one mark lower than needed for a correct exposure. I cross-checked it with two different TTL meters from two cameras. It might not be the most accurate test but it shows that it's a bit off.

    Thank you fine gentlemen for your replies!
     
  10. Sirius Glass

    Sirius Glass Subscriber

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