In the 90s, I traveled to Nova Scotia, Canada in the winter and then took a helicopter out to the pack ice to photograph baby harp seals off the coast of the Magdalen Islands. It was 45 degrees below zero, and surprisingly my medium format film camera, the Mamiya RZ 67, still worked. I was worried about the lubricants in the blades of the shutter freezing, but I didn't have a problem. With all the glare on the snow and ice, the most accurate way to determine the exposure was with a handheld light meter on incident mode. This measured the light falling onto the scene rather than measuring the light bouncing back from the snow and the white seals into the meter. The reflected method is how our modern cameras work, and that's why white or black in a composition can fool the meter. Incident readings aren't influenced by the subject matter. They read the true ambient light. I used a 250mm lens, equivalent to a 135mm medium telephoto in the full frame digital format. Based on the light in this shot, my settings would have been 1/250 at f/10 with Fujichrome Provia 100 film. We didn't use 1/3 f/stop numbers back then, so I would have set the aperture between f/8 and f/11.