Incident vs reflected: why cameras get snow wrong
Photograph a snowman on a bright morning with everything on auto, and the snow comes back grey. Not white — a dingy, dishwater grey, every time, on every camera ever made. The camera didn't malfunction. It answered the question it was built to answer, which turns out not to be the question you asked. Understanding the gap is most of what "learning to meter" means.
Two questions about the same light
An incident meter — the handheld kind with the white dome — stands where your subject stands and measures the light falling on it. It doesn't know or care what the subject looks like. A reflected meter — your camera's, a spot meter, and the one on this site — stays at the camera and measures the light bouncing back off the scene. Same photons, opposite ends of the journey, and one crucial difference: the reflected reading is contaminated by the subject itself. A white wall and a black wall under identical light reflect wildly different amounts, and the reflected meter can't tell "bright subject" from "bright light."
The 18% handshake
Reflected meters resolve the ambiguity with an assumption: scenes, averaged out, reflect about 18% of the light hitting them — the mid-grey of photographic lore. Landscapes with grass, trees, sky and dirt genuinely do settle near that number, which is why the assumption survived a century. The meter's suggestion, always, is "settings that would render this scene as mid-grey."
Snow breaks the handshake from above: it reflects 80-something percent, the meter reads all that bounce as excess illumination, cuts the exposure, and mid-greys your snowman. Coal cellars, black cats and dark wood break it from below and get lightened into grey soup. The meter isn't wrong; the world stopped being average.
Getting incident-style answers from a reflected meter
You can't screw a dome onto a phone, but three old tricks recover the incident answer with the tools present:
1 – Meter a mid-tone in the same light. Grass, weathered pavement, the north side of a tree trunk — spot-meter it and let the snow fall where it may. A pocket grey card makes this exact.
2 – The palm trick. Skin runs about a stop brighter than mid-grey regardless of complexion's exact shade. Spot your palm in the subject's light, open up one stop from the suggestion.
3 – Compensate by knowledge. Snow scene? Give it +1½ to +2 stops over the reflected reading. Night scene that should look dark? Pull 1–2 stops under, or the meter will helpfully turn midnight into dusk.
Which meter for which life
Studio and portrait shooters live by incident domes because subjects are reachable and light is the product. Landscape, street and wildlife photographers live at the camera position, where reflected metering — plus the three tricks — is the entire practical toolkit. The skill that transfers everywhere is the habit underneath: always know whether you just measured the light, or measured the subject wearing the light. The snowman only comes out white when you can tell the difference.