Q: I'm puzzled about retouching -- how do you do it? Do you retouch color prints the same way you do black and whites? I guess the most important question is, why do it? Is there a different reason for retouching a news picture than one that's not going to be published?

A: First, let's make a distinction between spotting and retouching.

Spotting is the cosmetic removal of spots, scratches or other marks when other methods (such as cleaning lenses and negatives) fail.

Retouching means changing the image -- alterations that can range from removing a flare from eyeglasses to separating a dark suit from a dark background to deleting an unwanted person or object from the picture.

From a physical standpoint, most people can retouch a black and white photo. You need not be an artist, just methodical and very careful.

In most cases, water-based paint is applied directly to the print. The paints come in gradations of tone ranging from black to near white. In a commercial or production setting, the colors are dispensed from tubes and mixed on a palette. They are applied with very small artist's brushes or an airbrush.

In some cases, very soft pencils can be used. These too range in tone from white to black.

The good part for us amateurs is that the paints and soft lead can be easily removed if you goof.

Retouching color is more difficult. You have to use a full range of colors, and a little bit of artistic talent helps.

A problem that now exists is the plastic finish on modern papers. The coating is so slick, and so waterproof, that normal applications won't hold so well. With black and white papers, retouching can be made to hold if you apply some concentrated photo-flo (a darkroom wetting agent) with a q-tip. Let it nearly dry and this should work. Another method I have seen used is the roughing of the surface with a common pencil eraser and then application of the retouching.

The "whys" of retouching are important. If for any reason there are marks spots or irregularities on the print, I see no problem removing them. But I am unequivocally opposed to retouching to enhance or alter a picture's meaning.

Happily, The Washington Post photography department does not retouch to change a meaning. Further, our photographers' negative quality is such that cosmetic retouching is usually unnecessary.

Q: Will you please explain the difference between flash and strobe? Are they different systems or are the words interchangeable? I have an Olympus Infinity camera that has a built-in flash -- or is it a strobe?

A: In today's practical applications, the words are interchangeable.

Technically, flash refers to flash bulbs. These are still used on some cameras, particularly the blue bulbs that are balanced for daylight color film.

Strobe refers to electronic flash. It evolved from the name Stroboscope, a rapidly flashing device originally used to measure the speed of moving objects such as armatures in motor shafts and record-player turntables.

In camera usage, this electronic light flashes at a high speed and "freezes" the subject being photographed. And you don't have to change it after each picture. (Strobes, too, are less bright than flash bulbs, making it easier on the subject.)

Most camera instruction books now refer to them as "flash" even though they are strobes.

Q: Some years ago while serving with the Army in Germany, I purchased a Voitlander 35mm camera. I never was much of a camera bug, so over the years I don't think I've taken more than 10 rolls of film. The camera appears to be in excellent condition. Can you tell me if it has any value, and if so, to whom?

Q: In 1973, while on a trip to Tokyo, I bought some Canon camera equipment at what was a remarkably low price.

I have two Canon FTQL cameras, plus a 35mm, a 200mm and a 55-135mm zoom.

They have served me well, and I have kept them in very good repair. But in the past few years I haven't used them very much.

I tried to sell them both in New York and Boston, but had no luck. Do you think I might have more luck in the Washington area?

A: Buying and selling used cameras is somewhat like buying and selling used cars. There's an element of risk. And most people prefer to buy new cameras, especially since today's high-tech equipment sells at a fair price.

Selling the Voitlander will be kind of tough, but I'm a little surprised that the FTQL Canons have not moved. I still have one in my bag and use it regularly.

In both cases, I suggest some telephoning to camera dealers in your area to see who might be interested in seeing your stuff. Some stores keep a list of area collectors, and may be able to help.

Also, check a publication called Shutterbug. It contains lots of information about older cameras.