Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,338   Posts: 1,537,721   Online: 796
      
Page 1 of 5 12345 LastLast
Results 1 to 10 of 47
  1. #1
    David Lyga's Avatar
    Join Date
    Nov 2007
    Location
    Philadelphia, PA USA
    Shooter
    35mm
    Posts
    1,236

    variance in camera light meters

    I have a Canon AE-1 and an Olympus XA. Both have working meters. Both deliver identical and accurate readings for daylight situations with, of course, the same film speed. But, oddly, the XA shows two to three stops less exposure needed under incandescent lighting than the Canon requires.

    Now, most of us know that color film requires about two stops less exposure under incandescent lighting (without the blue filter) than the same speed of traditional B&W film does under that same incandescent situation. This leads me to come to a possible (but erroneous?) conclusion that the Canon metering is optimized for traditional B&W negative exposure and that the XA is optimized for color (slide?) film. Comments? The XA metering is from a CDS cell and, I believe that the AE-1's cell is silicon blue photodiode. - David Lyga
    Last edited by David Lyga; 01-15-2014 at 08:13 AM. Click to view previous post history.

  2. #2

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,641
    In addition to possible calibration differences and the use of different standards by manufacturers, different types of cells vary in their spectral response.

    Differences could also arise from how much of the field the meter is measuring, which also means the test scene or setup is an important variable, which introduces other potential variables like flare.

    You haven't explained the test conditions beyond (outside/incandescent). What did you meter outside? A neutral grey card? What did you meter inside? Did the test cards fill the frame? What lenses were used? Light sources? Etc. Etc. Etc.

  3. #3
    David Lyga's Avatar
    Join Date
    Nov 2007
    Location
    Philadelphia, PA USA
    Shooter
    35mm
    Posts
    1,236
    No, Michael, I closed all options for variance other than the actual meter responses in question. I metered 'normal' scenes in both cases: outdoors, a park scene and, indoors, a room lit by a ceiling tungsten light. In all cases the field of view was virtually identical, obviating the possibilities of different reflectance values coming into the equation. I could not come to another conclusion than the one I posited. But, your assessment that different types of cells deliver different spectral responses is something that should be discussed more fully, as the manufacturers have not done that, ever, as far as I can see. - David Lyga

  4. #4

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,641
    Some spot meter manuals give some information with respect to how they were calibrated (k factor) etc. Spectral response has mostly to do with the type of cell, which means it can depend on how old one meter is relative to another, as the technology changed over the years.

    If you want to delve into meter calibration standards, linearity, theory etc., it is interesting stuff - be warned however - it is complicated. Richard Henry did some interesting testing in his book, and had some help from a very reliable insider at the time, but even that book only scratches the surface. Stephen Benskin has posted some interesting threads here.

  5. #5
    David Lyga's Avatar
    Join Date
    Nov 2007
    Location
    Philadelphia, PA USA
    Shooter
    35mm
    Posts
    1,236
    Yeah, but don't you think that the manufacturers should have offered this information freely? Amazingly, the 'public' seems to have never voiced concern with these spectral differences. It just seems that it is sufficiently important an issue to have been parsed and discussed at length, and, herefofore, seems to have been not even 'noticed'! Thank you Michael. - David Lyga

  6. #6

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,641
    What I'd say is that this is just another of the sensitometric theoretical issues (along with things like exposure theory, tone reproduction theory, etc.), which very few practicing photographers have any real knowledge of, but which ends up mattering relatively little to anybody from a practical perspecitve because of two things:

    1) The materials and processes we use offer so much latitude and flexibility that with practice we produce high quality outcomes by effectively working around all the differences between what we think we're getting and what we're actually getting from our metering, exposure, development decisions - without realizing it.

    2) There are so many variables (some beyond our control) piled up in the end to end photographic process that often some of them cancel out other ones, reducing the net "error" to manageable levels we can work with.

    How else can you reconcile the fact almost everybody is wrong about what is going on, and yet people can still make great prints!

  7. #7

    Join Date
    Nov 2005
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    5,036
    Quote Originally Posted by David Lyga View Post
    Yeah, but don't you think that the manufacturers should have offered this information freely? Amazingly, the 'public' seems to have never voiced concern with these spectral differences. It just seems that it is sufficiently important an issue to have been parsed and discussed at length, and, herefofore, seems to have been not even 'noticed'! Thank you Michael. - David Lyga
    These data (spectral response characteristics of metering cell technologies) are freely available. The "problem" is that they exist in supplier specifications and engineering journals. One must not only know how to access them, but know how to read and interpret that level of knowledge. I have seen such discussion in books on photographic metering too. As for the manufacturers, as long as their product meets their customer requirements (a decent exposure most of the time) then they have no need in educating on the underlaying engineering... escpeciall with regard to how it compares to a competetors. This is true of all consumer products. It is even mroe true when we are talking historical products.

  8. #8

    Join Date
    May 2006
    Location
    Aurora, IL
    Shooter
    35mm
    Posts
    1,953
    If anything I have to increase exposure for incandescent lighting with color film unless it's balanced for tungsten. Because the blue layer is underexposed color correction is not possible. Overexposure ensure adequate density in the blue layer. Extra density in the red layer doesn't matter much it can be filtered out during printing.
    I seriously think the XA is wrong and yet when the XA meter is wrong it could still deliver correct exposure because (like the OM-2) it has a meter circuit just for displaying and another totally independent circuit to do auto exposure control.

  9. #9

    Join Date
    Feb 2008
    Shooter
    35mm
    Posts
    197
    Is it the spectral response (against different spectral contents of incandescent vs daylight) or is it that one of the two meters is deviating from true response at low light levels (artificial light is typically much weaker than sunlight)??

    To sort this out you can try
    (1) with both cameras, meter in sunlight a piece of red paper, fabric, etc... Do they still agree?
    (2) with both cameras, meter incandescent lighht at high intensity, e.g., staring into bare bulb at same close distance. Do they still disagree (as much)??

    Would be interesting if you report the results here...

  10. #10

    Join Date
    Sep 2011
    Location
    Adirondacks
    Shooter
    Multi Format
    Posts
    3,381
    Quote Originally Posted by bernard_L View Post
    Is it the spectral response (against different spectral contents of incandescent vs daylight) or is it that one of the two meters is deviating from true response at low light levels (artificial light is typically much weaker than sunlight)??

    To sort this out you can try
    (1) with both cameras, meter in sunlight a piece of red paper, fabric, etc... Do they still agree?
    (2) with both cameras, meter incandescent lighht at high intensity, e.g., staring into bare bulb at same close distance. Do they still disagree (as much)??

    Would be interesting if you report the results here...
    It might be more telling to meter red, blue, and green, sunlight and tungsten - be very certain you actually have lightbulbs with filaments, not lookalike CFLs. Another informative experiment would be to meter in sunlight, both direct and in open shade, with and without a strong UV filter on the cameras.
    You might be surprised at what you see.

Page 1 of 5 12345 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin