Many readers have asked me for help in selling or appraising old cameras, which might be worth a pot of gold or simple dead weight.

What kind of cameras are collectors looking for? First, and quite obviously, the rare models. Many makes qualify in this category, but you have to know the exact model of your camera. For example, your Leica could be a IIIc model bringing from a low of $150 to $200 for a civilian version to a high of $2,00 to $2,500 for the Marine M17 version that was used in Germany.

Those prices are from the new Blue Book Illustrated Price Guide to Collectible Cameras published by Myron C. Wolf and obtainable from Photographic Memoribilia, PO. Box 351, Lexingon, Massachusetts 02173. Another source for such information is Price Guide to Antique and Classic Still Cameras, published by Centennial Photo, Box 3609, Grantsburg, Wisconsin 54840.

Besides the make and the model, Blue Book describes how the camera's condition can effect its price; the prices quoted are the actual prices at which cameras have been sold when in excellent condition.

Here are some rating guidelines. EXCELLENT CONDITION -- 80 percent to 100 percent original finish, similar to new, used little, no noticable marring of wood or leather, little or brassing, lens clear and clean, all mechanical parts in perfect working order. MINT CONDITION -- Add 10 percent to 25 percent to price listed for excellent condition. Mint means 100 percent original finish, everything perfect, in new condition in every aspect. VERY GOOD CONDITION -- Deduct 15 percent to 25 percent from listed prices -- 60 percent original finish; item complete but wood or leather slightly scratched, scuffed or marred, metal worn but no corrosion or pitmarks; lens and viewfinder clean; shutter and mechanical parts in working order; restorable with a minimum effort or expenses. GOOD CONDITION -- Deduct 25 percent to 50 percent from listed prices -- 45 percent original finish; minor wear on exposed surfaces; no major broken parts but may be in need of minor replacement parts; metal rusted or pitted in places but cleanable; leather scuffed and/or aged; wood scratched, marred and may have minor cracks, but restorable; the lens showing use, and the shutter in questionable mechanical condition but repairable. FAIR CONDITION -- Deduct 50 percent to 75 percent from listed prices -- 25 percent original condition; well-used and worn; in need of parts, replacement and refinishing; leather cracked or missing; lens clouded or damaged; metal parts pitted and gears rounded; shutter inoperable; wood finish almost gone and in need of complete restoration.

For cameras requiring repairs, deduct the estimated cost of repairs from listed prices.

This gives you an idea of just how exacting and complicated dealing in collectible cameras is -- you have to know not only the going price for your camera, but the condition and the trends that drive the market up and down on certain makes, depending on demand.

It may seem too much trouble to follow through and find out if you have a Lulu or a lemon. But the rewards are worth the bother: At a recent auction of photographic equipment at Christie's in New York, some of the prices were astounding. A black Leica IIIg made in 1960 for the use of the Swedish air force was bnid at $9,000 to $11,000; another "Reporter model 1937 Leica at $4,000 and other rarites such as a Loman (who ever heard of that one?) single-lens reflex 1889 model at $7,000.

The best advice I can give, which I wish I'd had when I sold some of my cameras, is to shop around.

Get the best information on the going rate for the camera you have, then advertise it for sale in publications like Shutterbug Ads, Box F, Titusville, Florida 32780. You local paper is also a good bet, in the classified ads under photography.

Or simply contact camera clubs in your area and ask about swap meets, or members interested in the particular model camera you have. Q. In a recent column you stated that custom prints can be obtained in under one half hour from a company called One Hour Photo. I have been in the photo lab business for over 30 years and I think that you are not only wrong but are also misleading the public.

The machinery you described is not custom-type, in fact, it has all but been eliminated from the real custom labs that deal with professional photographers and advanced amatuers.

Professional color laboratories are now using video analyzers to analyze each frame to fully color correct it prior to printing. The negatives are then printed on computer controlled printers that use this data. Ameteur photofinishing labs have also changed from the printers you mentioned to new and sophisticated computer contolled printers that eliminate the "guess-work" on the part of the operator.

You also mention low cost, which again is misleading since our company provides custom printed, video analyzed color proofs for only $11 per 135/36 roll. A. I have personally checked out the service offered by the One Hour Labs. The printer used is a QP-3500 Noritsu which is so new that not many have heard about it. The QP-3500 Noritsu is a computerized operation with an optional override for manual correction. The prices charged are in line with commercial labs for amateur processing -- but with the added advantage that the customer can see the prints right on the premises and can have the reprints made immediately if not satisfied. The information on this service was published because of the uniqueness of the quick personalized service and not with any thought of not crediting the excellent, sophisticated operation of many professional laboratories.