Some films are slower in tungsten lighting, some films are faster. There is no "General Truth" to any statement about sensitivity, just a lot of lesser "special truths".
Vegetation also varies a lot in spectral reflection, so I can't give general filter advice: sometimes a light blue gives better separation, sometimes orange or even warm-up, and other times not even deep red will do the trick. Confound this even more with the different spectral sensitivities of different films...
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-- Ole Tjugen, Luddite Elitist Norway
Some films are slower in tungsten lighting, some films are faster.
Dear Ole,
Very true, and the figures are almost never given nowadays. Either way, for pan/hyperpan films, it's seldom more than 1/3 stop. Of the figures I've seen, more are faster to daylight than tungsten, though T-Max films seem generally to go the other way. That still doesn't alter the fact that 'sensitized to tungsten balance' is effectively meaningless when referring to monochrome.
Nor does it alter the fact that filters lighten their own colour and darken their complementaries. Different shades of green may be unpredictable; but take green foliage and brownish earth (or indeed brownish tree-trunks) and green or orange will lighten the one and darken the other.
[QUOTES=Roger Hicks]
"Dear Dan, Um... Film is inherently sensitive to
blue/violet/ultraviolet. Dye sensitization extends
that to green/yellow (ortho), orange/red (pan) ..."
Our usual B&W Films are sensitized well into the red.
When so the green through red sensitivity is well below
the film's inherent blue and shorter wave length sensitivity.
Manufacturers have failed to bring emulsions up to blue speed.
"...the statement that B+W films are 'sensitized to tungsten'
comes very close to sheer nonsense." Cheers, Roger
Good thing I didn't say that. I wrote, "...spectral sensitivity
is balanced across a band around 2800K..." All that is needed
to confirm is a look at any manufacturer's film data sheets. If
blue speed were possible across the spectrum we would
have much higher speed emulsions. Dan
As for filtration under the canopy my only concern is image fidelity. For example I've photos where a trail of rock and
earth is less seperable from surrounding green flora than
I judge true to the scene. Dan
But how did they meter? If the flora and earth/rock meter the same, then of course they blend in together. A red ball will pop out visually to the eye when sitting on green grass, but if they metter about the same, then in B&W the ball will not pop out visually on the film. Not really about panachromatic B&W film's responce to color, but the intensity of light reflected off the ball and the grass.
Now, the amount of light objects are reflecting might change due to the color balence of the light hitting them, but your meter will tell you that. Your brain is differentiating between the earth and the flora on the basis of color...but your film is differentiating between them based on the amount (not color) of light reflecting off of them.
In your example, you may wish to use a filter to seperate the values of the earth and the foliage -- green to lighten the flora relative to the brown earth...or an red/orange filter to darken the flora relative to the earth.
I suspect that there is a considerable distortion of the available light's color balance at the forest floor where
little if any direct sunlight may be visible.
The usual B&W films are color balanced for tungsten but
wonder if a light yellow filter filter goes far enough towards
muting the preponderant available blue. Would an orange
filter be more correct? Also, yellow or orange, would
filter factors need to be increased in such a blue
blue-green environment? Dan
Consider the chance you are thinking this out waaaay too much. Sure, thought is good in general, but there's a time and place, and it aint now.
Just go shoot "the forest floor" and see what you get. If you are shooting flowers or something with a strong color, against a contrasting colored background, filtration will be useful for special effect, but the forest is bland color wise, and generally will not respond usefully to any color balance corrections you may impose, other than to make your exposures longer.
Forest light never stopped Wynn Bullock, A.A., Weston and co, and they all got amazing images without worry about the exact spectrum of the forest light. Heck, you can get pretty far with color film in the woods without elaborate color correction. Maybe a uv/sky filter or a modest warming filter would be fine.
Had you a very accurate color meter system, I'm sure you could discern some sort of very modest slant to the spectrum at the forest floor, but with any BW film having a fair claim to being panchromatic, there will be no show stoppers whatsoever if you shoot with no filtration.
The worst issue is likely to be contrast if the day is sunny, since any patches of direct sun will be far above the predominant brightness. I love gray days.
Best,
C
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I'm old school...take one photograph as you would normally, take one with the experimental filtration/exposure/development/whatever, take notes, print them both as proof prints, then compare.
This serves two purposes; it gets you out photographing and it gives you real life results you can hold in your hand
Murray
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Note to self: Turn your negatives into positives.
Our usual B&W Films are sensitized well into the red.
When so the green through red sensitivity is well below
the film's inherent blue and shorter wave length sensitivity.
Manufacturers have failed to bring emulsions up to blue speed.
If B&W films had across the spectrum sensitivity equal to their
blue sensitivity we would have Daylight B&W film. To use indoor
a blue-ish or cyan filter would be needed.
Daylight B&W film might be possible. As it stands a blue
de-sensitizer would need be found. Dan
Dan, take a look at the sensitivity curves for Ilford FP4+.
It has reduced blue sensitivity compared to most other films.
A "blue de-sensitizer" is easy: Yellow dye. I don't know if that's what Ilford uses, but I like the colour response of FP4+ better than other films I've tried for most outdoors work.
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-- Ole Tjugen, Luddite Elitist Norway
They are? Anyway, having done B&W under 300 feet or so redwoods for the past 30 years, I have never worried about it a bit. And unless one is doing some strange highly detailed scientific study, I see no reason to give it a second thought.
Vaughn
My biggest problem shooting in forests has nothing to do with spectural response of the film but with the extreme contrasts. Dark shaded areas with patches of bright sunlight bursting through - magic stuff.
I have begun to experiment with overexposed XP2 in my 6x12 back - the images from my trip to Weott were really good - even sold a panoramic last weekend at a local show. The other benefit of XP2 is has really good reciprocity characteristics - handy when you can get into multiple second exposures.
By the way - I will be heading up to Weott & the Matole Road for the second part of my field trip - love that area
Linear Mode
