Q. I haven't had much experience with filters, but I heard a couple of people who are really into photography talking about them. They made the subject sound very complex and very difficult. Is the subject important enough to worry about? After, all you can't use filters on color film.

A. This is a very important subject. Generally, I have a filter in front of every lens I own. I use a skylight or a UV filter. There's not a lot of filtration in either, but they serve to "clear the air." They do indeed filter out some ultraviolet and give some warmth to your photos.

Moreover, these filters serve as protectors for expensive lenses. It hasn't happened very often, but I can recall occasions when my skylight was broken but the lens was unscratched.

Another filter you might want to consider for all shooting is the polorizing filter. This one is valuable in reducing reflections and adding contrast in both black-and-white and color films.

I also recommend the 81-A filter for color. This can be used for natural light or with electronic flash and will serve to "warm up" the flesh tones of your subjects.

For black-and-white film, there are three basic color in filters, with gradations within each: yellow, green and red. The basic purpose of any of these is in improving contrast.

The yellow filters boost the natural contrast and things appear a bit sharper.

The green filters add a good bit of contrast, but I have found them most effective in very bright sunlight.

Red filters increase contrast the most, and can give wonderful special effects, such as a pitch-black sky with chalky-white clouds.

It's very important that you read the directions or talk at length with your camera store salesperson. Most filters cut the light don and can cause underexposure, so beware.

Q. I like to shoot black-and-white film, but I've had some problem finding places to have the film developed. I realize that most people prefer color and I guess there are a million places to have it printed. Not only that -- it's hard for me to find black- and-white film. Where are the black- and-white processors?

A. They're not far away. Look in the Yellow Pages. There are dozens and dozens. This letter, however, peaked my curiosity, so I started making some phone calls.

You're right, not all places sell black-and-white film. I did find, however, that all the camera stores I called do sell it. In fact only some of the drug and grocery chains didn't sell black-and-white.

As to processing: I talked with two major drug chains and the two biggest supermarket people. They all handle black-and-white processing. I spoke to nearly all the photographic establishments and every one said they handle it.

Prices and services vary widely.

Processing and printing (31/2i X 5i) of a 24-exposure roll ran from less than $6.50 to more than $11. Work times ranged from three to 10 days. One custom lab charges for processing and a contact sheet, but will then consult with you on what frames you want printed -- blowups only.

In these days of high-tech color processing, there's no doubt that color processing and printing costs less than black-and-white. Some places handle black-and-white only as a special service.

But I was impressed with the way the drug and grocery chains deal with photo finishing. They are all expanding photo services and making considerable efforts at customer satisfaction.

There's no doubt in my mind that interest in black-and-white is growing. It's a most creative medium.

Carl Kramer, former director of photography for The Washington Post, will try to answer your photography questions in his column, but cannot reply individually. Send your questions to: Carl Kramer, c/o Weekend, The Washington Post, 1150 15th Street NW, Washington DC 20071.