Shooting over snow or a beach, you usually want to increase the exposure. The exposure bias control is handy for that when using auto mode.
On cameras without aperture control, an ND filter reduces the amount of light reaching the sensor and requires increasing ISO or decreasing shutter speed.
Okay we’re talking about some different things here.
First to be clear I don’t use auto exposure. I use zebras to set peak using manual.
In the case of snow, the lit snow would indeed be at the top of the exposure. But also not relevant to what I’m talking about.
If you want smooth cinema like motion, whether the camera’s or an object in scene, you want a shutter speed that is very close to 50% of the frame rate… (or 1 divided by 2x the frame rate depending on how you want to do that math.)
If shooting at 24fps, each frame is 1/24 of a second, therefore you want 1/48 of a second exposure. 1/50 is the close equivalent on these. Of shooting slow mo at 120 fps, then a shutter of 1/240.
1/50 is wide open for daytime even at 100 iso. At least on the Minis, you can’t go slower than 100 iso. And if you shorten the shutter duration you’ll start to get that “saving private Ryan” look.
The way to fix this is an ND filter. With daytime clear sky you’ll need about 5 to 6 stops of reduction.
I like to shoot magic hour, so the variable 1-5 is ideal, I can fly back to quickly adjust the ND without landing (sport mode hand grab with one hand, dial the ND with the other).
EXPOSURE
Only if measuring the light through the lens or with a spot meter, would you say that you need to increase exposure, but actually you don’t. If you measure the snow itself TTL/spot on a clear day not in shade, you’re going to want to put that at the top of the range, close to clip.
That said, taking a spot or TTL reading of day snow is usually not best practice. These are situations where zebras are super helpful.
If using a meter, use the integrator, in recess, pointed to the source (sun) as you would for flash.
But snow notwithstanding what is the subject? Let’s say a cute blonde snow bunny. Well she’s standing on a gigantic white card. She’s over lit, and her blonde hair will probably blow out if you shoot at meter (integrator) though here’s a place to spot read: spot read her hair on the sun side and put it half a stop to a stop under the digital brick wall (clipping), or use zebras and back off half a stop under zebras on her hair, or a little farther to have just a few zebras on the snow.
In these cases, a subject on the snow, we are definitely reducing exposure to expose the subject inside the range.
If I’m shooting stills with Nikon, I routinely shoot raw and one stop under, and bring it up in Lightroom. This preserves highlights and allows an hdr post process.
Can’t really do that too much on 8 bit video, but 10 bit log you can to a degree, half a stop to a stop under prevents that nasty video clipped look. With 10 bit log you have room to move around in post (not as much as raw, but workable).
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