Filters that might darken the sky without also diminishing shadow detail?

You might try a polarizer.

These are sensitive to the direction of the light, being most effective when the camera is pointed at 90° to the light source.

Obviously if you're shooting a sunset the polarizer won't work.

- Leigh

Thanks Leigh. (I'm actually an experienced color photographer, but have only been seriously interested in B&W for the last few years; I'm not sure if I placed this in the proper classification, but it didn't seem to fit others.)

I might well experiment with your suggestion next time out. But i'm thinking of a recent image, especially, where the sun was almost down and it was pretty much in front of me where a polarizer wouldn't be very effective, of course. And in another, an image of the ruins of a building, well into dusk... In both, the sky seemed too bright.

Hi Jeff,

Those situations are very difficult. I can't suggest any reasonable solution.

The 'standard' filter for enhancing clouds is yellow (negative blue), but you said you already tried that.
It really won't work at dusk anyway because the skylight has so much yellow in it already.

- Leigh

Hi Leigh,

I kind of think you may have really clarified the problem for me with your last sentence... I hadn't thought of that. I'm now thinking that perhaps by using the yellow filter, I am actually making this problem worse at dusk. If so, thanks for clarifying that.

I was reading about red filters today, in case you or someone else might be familiar with them. It seems that they darken the sky, but I'm afraid that one of them might also ruin darker foreground detail by the increased contrast..

Though it's used more with color than B&W, a graduated neutral density filter should work, as long as you have a reasonably straight horizon line.

One obvious problem that occurs to me about a red filter in low light is the filter factor -- if I recall correctly, an #25 filter has a factor around 2.5 stops and a #29 takes three stops. If you're starting with low light, that could lead to some pretty long exposure times.

The shadows tend to be on the bluish side, so a red #25A dims them down quite a bit. A good GND might help.

It does seem, as Jerry Coffin suggested, that a ND grad should help.

It depends to some degree on the color of the shadowed areas. If it is organic and green, a green filter might be worth trying (red would just worsen the situation, as it also does with blue casts in shadows (as one sees in shadoiws on snow or sand). if you have a digital camera handy, put it into B&W mode and try the green, orange, red and yellow filters. Otherwise, try these different filters with your film camera and check the shadow areas of your developed negatives for detail. A graduated neutral density filter should also be tried and, as suggested above, may be the best solution for your particular problem of low sun or dusk photography.

Try an orange filter. It darkens blue skies without excessively darkening most foliage. That's why I prefer it to red, which will darken most foliage significantly.

You can also try graduated neutral or color density filters.