B/W Light temperature?

[ryanmills]

Do black and white pano films favor one color temp more than another? Specifically a standard warmish soft white CFL vs a daylight CFL. I saw a post Alex Timmerman's made testing different types of lights for wet plate. I'm testing an idea shooting inside with long exposure using CFL blubs. I was reading his post and it got me to wondering yes, there are X lums hitting the meter, but are they as strong or is the film as sensitive to that color, would I need to an extra stop or drop one? I assumed daylight bulbs would be best but now im wondering if something warmer like a normal bulb would be stronger, or does it just add more contast? Or does it matter either way?

Alex Timmerman's Post: http://collodion-art.blogspot.nl/201...-light_15.html

[Mark Woods]

Silver emulsion is only sensitive to daylight. That said, it's the tricks of the chemists that allow Panchromatic and Color films. If you look at the the B&W film ASAs, you'll see that in a tungsten environment the film responds 1/3 stop slower. This is pretty accurate with Kodak films. I do the same compensation for Ilford film stocks. Test. Test. Test.

[ryanmills]

Interesting, guess I will have to tinker a little.

[Mark Woods]

Enjoy the journey!

[Kirk Gittings]

"Silver emulsion is only sensitive to daylight."

What does that mean?

[ryanmills]

I assume he means its most sensitive around 5600k, unless someone has other info?

[Leigh]

Color Temperature, as that term is applied to photographic film, is the ratio of red to blue light.
It does not know or care anything about green.

This makes sense since the emissive spectrum of a thermal light source is highly predictable.
If you know the red and blue components you can accurately predict the green level.

It gets very confused by any source that does not follow the nice even spectral curve of a thermal emitter.
This is why good color temperature meters have a separate green/magenta channel to check that value.

The problem tends to be acute with fluorescent emitters, which have a huge spike in the green range.

- Leigh

[Mark Woods]

All of the film emulsions based on a silver halide only respond to daylight, approximately 5600* to 6000* or higher (hence the used of UV filters at high elevations). Only through dye masking is color achieved or panchromatic response achieved. This is also the reason why B&W films have a lower ASA in Tungston light. Regarding the green emulsion in color film, it can be problematic since part of the imaging in HS films has been shifted to it and reduced from the blue emulsion. This can be very tricky to time out, and if one knows the amount of increased density of the green emulsion, one can use a CC Magenta to correct it to the "ideal" density. BTW, there is no stop compensation when doing this since the CC Magenta only affects the green emulsion.

I hope this helps. It's probably TMI. :-)

Mark

[Drew Wiley]

At this point in the evolution of the light bulb (or in this case, a technological de-evolution backwards), CFLs tend to have a pretty wacko spectrum. So you have
to test specific films in relation to specific bulbs. This will affect both the speed (ASA) of the film as well as how various colors translate into relative gray values.

[Drew Wiley]

Given the intended application, I should have clarified something else. CFL's being designated as "soft white" or "daylight" are just marketing labels based on alleged
ability to substitute for ordinary lightbulbs. The spectra is otherwise discontinuous, unpublished, and unreliable. In other words, those terms mean very little from
brand to brand, or even within the offerings of a specific manufacturer, when attempting to relate junky consumer CFL's to tungsten filament counterparts. There is
very little standardization of this kind of thing. So again, you just gotta test, test, test.