Have we changed the manufacturing process which we could now ignore the lighting condition for film speed?
It's pretty much the spectral sensitivity of the photo cell in the exposure meter and what color temperature to which it was calibrated. Stimson, Allen, An Interpretation of Current Exposure Meter Technology, Photographic Science and Engineering, Vol 6, No 1, Jan-Feb 1962.
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You can find more papers at http://beefalobill.com/benskin/content.
That paper is from 1962, is there anything more current?
I'm working on a light-meter calibration light source and am seeking more info.
What about the exposure meter standard? It has a section or two on the light source.
That paper is from 1962, is there anything more current?
I'm working on a light-meter calibration light source and am seeking more info.
I'll be glad to look up any questions you have about these references.
That's all I know and it doesn't seem entirely sensible to me but... it presumably is where the separate tungsten film speeds started to become unnecessary. Most likely the actual 1961 standard explains the reasoning more thoroughly and it probably makes sense; I'm just not seeing it.
For panchromatic film the difference is about 1/3 to 1/2 stop.
An Interpretation of Current Exposure Meter Technology which ic-racer referred to in an earlier post answers the question as to the color temperature change in the calibration light source.
Studio flash largely killed off tungsten lighting, and these days people used Daylight balanced LED.
Hi, without giving this much serious consideration, I'd be inclined to guess that it's more likely to have been an exposure meter consideration.
If you have any of those older film data sheets I'd guess that they are just saying to set the exposure meter to such-and-such (lower) exposure index for tungsten lighting. Which roughly means that a "normal" metered exposure is fine for "daylight," but would tend to cause underexposure under tungsten light. So, to correct for this they recommend setting the meter to some lower "film "speed."
I'm guessing that modern exposure meters have a spectral response more similar to a (panchro) film, and thus changes to the meter's "film speed" are no longer needed. But... in the case where the meter's spectral response is different from that of the film (ie your case of Ilford "ortho" film) then some adjustment to the meter setting is still called for.
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