Q - I recently got into "pushing" film. Would there be any difference between pushing a slow film, such as Plus X (ASA 125), to ASA 400 and using Tri-X at its normal rated speed of ASA 400? Also, do you always have to double the film speeds? When should one "push"?

A - "Pushing" is just a fancy term for overdevelopment. Any film can be overdeveloped, but you have to take the consequences in increased grain and contrast. For this reason it's not a good idea to push film unless you absolutely have to, or you want the special effect of the increased grain.

It's better to change to a faster film than to push a slower one to the same speed, because each film performs best at its rated ASA. You don't necessarily have to double the film speed each time, but it's more convenient that way for the labs since they can then calibrate their development.

The best time to push a film is when the light level is too low for the rated speed. Quality of light is also important. If it's flat without contrasting darks and highlights, you can safely increase overdevelopment. In fact, the increased contrast gained may even be an advantage. Examples are night scenes, heavy overcast days, shade and before sunrise and after sunset.

There are additives on the market, such as FACTOR-8, that minimize the contrast and increased grain caused by overdevelopment. I've seem examples of Tri-X pushed to ASA 3200 with this product that compare with Tri-X developed at its normal ASA of 400.

Q - I'm taking my camera on a ski trip. What precautions should I take to protect it from the snow and cold? Are there any special techniques for snow exposures?

A - The neat plastic containers that can be strapped to the body - which look much like the first aid kit bags the ski patrol uses - would be ideal for protecting the camera.

There is nothing more annoying than having to carry on over-the-shoulder camera bag or having the camera dangling around your necks as you whizz down the slope.

If you're out in extreme cold and come into a warm room, moisture may condense on your lens. To avoid leave the camera in your bag and put it on the floor where it is cooler and let it warm up gradually.

Snow exposures can be a problem because your camera meter is basically calibrated for an 18 per cent gray reflectance, which is not suitable for white snow or darkly clad skiers, especially when backlit. The cure for this is to move in close if you want detail in the faces on a backlighted snow scene so that your meter will read the dark areas.