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  1. #61
    Helen B's Avatar
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    It was a very badly made wheel to begin with, and should have been recalled a long time ago.

    Best,
    Helen

  2. #62

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    Quote Originally Posted by Helen B
    "... It was a very badly made wheel to begin with, and should have been recalled a long time ago..."
    That's good to hear. All these years I thought it was something I had done to the photopic optic -- probably something having to do with its non-linearity or its spectral intensity. But now that you mention it, the rubber was kinda hard. And the lux flux was all rusted.

    Thanks for clearing that up. ;-)

  3. #63
    Helen B's Avatar
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    I hope that the graph is legible. It compares the CIE photopic luminous efficacy (in lumens/watt) with the spectral sensitivity of 400TMY and P3200TMZ (reciprocal of exposure in ergs/cm² to reach 0.3 above D-min, not a tungsten wedge spectrogram as used by Ilford for example). You can see the big difference at the blue end of the spectrum. (edit: I attached the wrong graph - this one is part log, part linear on the y-axes. I'll fix it later)

    If incident (illuminance) readings were being used you could calibrate an industrial light meter for use with film if the light source was fairly consistent in terms of spectral distribution. You probably couldn't use the calibration in other lighting conditions.

    Best,
    Helen
    Attached Thumbnails Attached Thumbnails photopic.gif  
    Last edited by Helen B; 06-30-2006 at 08:35 PM. Click to view previous post history.

  4. #64
    Helen B's Avatar
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    Too late to edit and replace the graph. Here is a version with both vertical scales linear.

    Out of interest I decided to have a look at what the ISO have to say about the spectral response of photographic lightmeters because I knew that they specify the calibration factor in terms of lux or cd/m², whichever is appropriate, not in terms of radiant power.

    The ISO suggest that the calibration should be made at a correlated colour temperature of about 4700 kelvins – a ‘reasonable compromise’ between daylight and tungsten. The spectral behaviour of the meter is determined by comparing the meter with a meter conforming to the CIE standard (photopic) observer under two CCT conditions: 2855.6 kelvins and 4700 kelvins.

    These are just ISO suggestions and not requirements and there is no need for manufacturers to follow them.

    Best,
    Helen
    Attached Thumbnails Attached Thumbnails linearphotopics.gif  

  5. #65
    Lee L's Avatar
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    Thanks Helen.

    Lee

  6. #66

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    I did not read what other have said, but I find my Pocket Spot meter by METERED LIGHT CO, can read better in lower light conditions then any other meter. It can read down to a -2 actually.

  7. #67
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    Quote Originally Posted by Ryan McIntosh
    I did not read what other have said, but I find my Pocket Spot meter by METERED LIGHT CO, can read better in lower light conditions then any other meter. It can read down to a -2 actually.
    Thank you Ryan. If you are linterested in better capabilities you might find reading the rest of the thread interesting.

    John Powers

  8. #68

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    Hi !
    I'm late on this discution, but :
    1) the Luna Pro and Lunasix 3 are the same emters. (different marketing strategies/pricing at the time)
    2) all Lunasix 3 /lunapro using 1.35V mercury batteries can be converted to use 2x1.55 V silver oxyde (gossen sells an adapter which is sold new in the actual Lunasix S which is IIRC still made) B&H has it.
    3) I've made a lot of "availlable light" photography in the past and relied on my "nose" and guessing to measure the light. I used always the same film (Fuji RDP ) and exposed for 20 to 45 seconds. And make bracketing up to 1min, 2 min and 3 min. I've always got one picture which was technically correct. Bear in mind that YOU SHOULD stop down from wide open to get rid of coma and chromatic aberations seen at these openings. If you calibrate the process, once your eyes are accustomed to the low light level, you can quite predict how much exposure you need.
    4) IMHO the tripod problem is more important than the meter problem... finding a stable and sturdy tripod able to hold still a camera during these long exposures and light enough to be carried on location is a real challenge...
    Hope this helps !

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