Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,826   Posts: 1,582,045   Online: 753
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 24
  1. #1

    Join Date
    May 2013
    Location
    US
    Shooter
    Large Format
    Posts
    2,060

    Spectral Response of Meter Cells?

    There is currently another thread broaching the subject of spectral response of meter cells (link following this sentence), but I decided to introduce a new one so as to be more focused on the question. Link: http://www.apug.org/forums/forum52/1...ml#post1610075

    Hopefully I can draw some knowledgeable responders on the subject. Perhaps put another way, black and white film tungsten ratings, or metering in other lighting conditions than daylight. I believe it is universally accepted that exposure meter sensitivity is planned to be in the 5600K neighborhood of color temperature. But what about metering in other lighting? What sort of allowance should be made for the meter's non-linear behavior in different kinds of light? I post here a link leading to the spectral response of one single distributor's product, a CdS cell: http://www.token.com.tw/resistor/photo-cds.htm

    But I have never undertaken a study on this subject. I'm just a person who has experienced a lifetime of poorly exposed negatives and never considered why. Now interested in the subject, I put forth this thread fishing for responders who may be better versed in the matter. This one link I just posted is my first step in the study of the matter. Hardly a definitive treatise. Any input welcomed.
    Last edited by Tom1956; 02-14-2014 at 12:40 AM. Click to view previous post history.

  2. #2

    Join Date
    May 2011
    Location
    South Africa
    Shooter
    Multi Format
    Posts
    460
    Images
    14
    Well, the obvious goal is to match the spectral response of the film and the meter. In simplest terms, that means you could calibrate your meter by metering off specific colours and doing step-wedge exposures and seeing what EI for what colour gives the best exposure. Newer matrix-type SLR metering systems are colour-aware, and therefore do the compensation for you, as do the more advanced studio light meters. If as you say your negatives are perpetually badly exposed, I can only suggest that you consider more sophisticated equipment or do a series of tests with what you have and compensate accordingly. Last but not least, bracket whenever practical to do so.

  3. #3

    Join Date
    Sep 2006
    Location
    UK
    Shooter
    35mm RF
    Posts
    3,523
    As well as the/a meter material data sheet a meter may have a sharp cut IR filter - like a M8 needs to avoid purple sheens. DSLRs can have hot filters alas I don't do DSLRs...

    Then you need the each films data sheet spectral response.

    The films I use have significant differences from near infra red traffic surveillance to ortho!

    The light does vary in colour temperature you can get colour temp meters.

    Tungsten light (colour) is dependent on mains voltage (your enlarger may be stabilised), bulb type, dimmer setting. Movie film can have a meter setting for tungsten and daylight 5222 has.

    But setting meter to the pre 1961 speed rating is simple or using C41 mono like XP2 at 200 ISO.

  4. #4
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,564
    Images
    46
    Here's a fun thread cross-reference:

    http://www.apug.org/forums/forum48/1...itivities.html

    So you have human eyes which see a peak at green, film which sees a peak at blue, meters which see a peak at red*... Good luck lining any of them up.

    *the Weston Photronic cell (I picked a fairly red-sensitive meter cell deliberately to present the worst case scenario).

  5. #5

    Join Date
    May 2011
    Location
    South Africa
    Shooter
    Multi Format
    Posts
    460
    Images
    14
    If there were to be a meter with colour awareness into the IR region, it would be dandy to be able to select the film type (loaded as a curve into the meter) or at least be able to define a custom curve. But it means a meter manufacturer needs to make a programmable meter, possibly augmented with built-in or add-on filter sets. Imagine, you don't set the ISO, you select the film itself. Everything taken care of.

  6. #6

    Join Date
    Sep 2006
    Location
    UK
    Shooter
    35mm RF
    Posts
    3,523
    Quote Originally Posted by dorff View Post
    If there were to be a meter with colour awareness into the IR region, it would be dandy to be able to select the film type (loaded as a curve into the meter) or at least be able to define a custom curve. But it means a meter manufacturer needs to make a programmable meter, possibly augmented with built-in or add-on filter sets. Imagine, you don't set the ISO, you select the film itself. Everything taken care of.
    An Leica M8 and a steep cut IR and steep cut Red filter would do, they are getting cheaper, the steep cut IR was free with new ones (M8) for a while. If the meter fails trash can.
    A custom meter might be more expensive.

  7. #7

    Join Date
    Aug 2006
    Location
    Hamilton, Ont, Canada
    Shooter
    Large Format
    Posts
    1,082
    Do we have to distinguish between reflective and incident meters in this thread. I ask because I can't imagine the point of specifying the 5600 k incoming light if the metre is measuring reflected light.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  8. #8

    Join Date
    May 2013
    Location
    US
    Shooter
    Large Format
    Posts
    2,060
    I wonder what Brian Shaw said before he deleted it. He's one of the reputable names on here. I'd have liked to heard it. I wish the one site I found a data sheet on the CdS cell had not passworded their PDF, so I could bring it into photoshop and crop the response curve to post here. It was very enlightening. But suffice to say it was VERY peaked in it's sensitivity range. Enough to make you wonder how these meters are calibrated and what film speed compensation must be considered outside that peak. And another thing--back before about 1970, B&W film had a daylight rating and a tungsten rating. I always assumed it was the film. Now I wonder if it was because of meter color sensitivity. And if so, why doesn't the film manufacturer have a tungsten rating now? Why did they drop it?

  9. #9

    Join Date
    Sep 2006
    Location
    UK
    Shooter
    35mm RF
    Posts
    3,523
    HiTom

    Double-X Kodak's cine mono still has a tungsten and daylight ISO.
    Probably for three reasons
    Think it is quite blue sensitive
    The cine people are more critical on exposure than stills
    Not many people use tungsten studios?

    Noel

  10. #10

    Join Date
    Jul 2010
    Location
    Southern USA
    Shooter
    Multi Format
    Posts
    4,126
    Quote Originally Posted by Xmas View Post
    HiTom

    Double-X Kodak's cine mono still has a tungsten and daylight ISO.
    Probably for three reasons
    Think it is quite blue sensitive
    The cine people are more critical on exposure than stills
    Not many people use tungsten studios?

    Noel
    I think your second reason is the most probable. The difference between the two values is only 1/3 of a stop. The fine grain positive stock on which the negatives are printed has little latitude. Still films probably have similar values but it is not critical for still exposure.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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