Q. The word "custom" seems to be associated with photofinishing. I'm not sure what it means. Is it something I should be looking for when I take my pictures in for processing? Does it have to do with enlargements? Is it different than "regular handling?"

A. The basic ingredient in custom processing or printing is individual handling. Custom processing is expensive, and rightfully so. Each custom print is inspected for color, sharpness, smudges, etc. Everything that can be done to get the best from a negative will be done.

Usually, custom printing even includes custom cropping.

I don't have custom enlargements made very often. The "regular" prints are generally fine.

I like to have my film processed my the manufacturer whenever possible, but have used drugstore and chain store processing with success.

No matter where I take my stuff, I insist on high quality, though. If I don't like the results, I ask for a reprint. I don't remember anything except the highest cooperation on the part of the camera stores. In fact, I have had things sent back at the suggestion of sales personel at my camera store. The chains are less personal but, after all, have other things to sell besides photo processing. DARKROOM SPACE

Several weeks ago, I asked for help in finding darkroom space for rent. Here are some places I've learned about:

THOMAS JEFFERSON COMMUNITY CENTER -- 3501 Second Street S., Arlington. 553- 8618. Facilities for black-and-white and color processing.

The current hours for black-and- white darkroom work are: Monday and Thursday, 9 to noon; Saturday and Sunday, 1 to 5:30; Wednesday and Friday, 6 to 9:30 p.m.

There is a $2 charge for each time block in the black-and-white lab. Non-members of the center are charged an additional $3 guest fee for each use. Residents and non- residents of Arlington County can become center members. The cost of joining is $20 per year for Arlington residents, $85 for non-residents.

As for the color darkroom, it's equipped with a color enlarger and and an analyzer, and members can rent it for $5 for a three-hour time block. There is an additional fee of $2 to $3 for non-members. Rental is by appointment only.

RESTON COMMUNITY CENTER -- 2310 Colts Neck Road, Reston, Va. 476-5000. Has a complete photography lab for black-and-white processing only. There are five Bessler enlargers and equipment to handle 110, 126, 135 and 21/4 negatives.

Each person is required to bring his own photographic paper. Everything else is provided for developing, including chemicals.

Lab fees are $4 per session for Reston residents and $6 for non- residents.

Lab hours are: Tuesday, 2 to 4; Saturday, 1 to 4; Sunday, 1 to 4.

Call for reservations.

PHOTOWORKS -- Glen Echo Park, MacArthur Boulevard, Glen Echo, Md. 229-7930. Has facilities for all kinds of black-and-white processing, from 35mm to 4x5. You supply your own paper, and Photoworks supplies the rest. The cost is $4 per hour.

The darkroom hours are: Sunday, 1 to 6; Thursday, 7 to 11 p.m.

PHOTO CITY -- 13079 Wisteria Drive, Germantown, Md. 301/428- 3307. This is basically a color establishment. It has three darkrooms, each with a color enlarger and a color analyzer. You can bring your own paper or buy it there. The darkrooms rent for $8.50 for the first hour and $6.75 for each additional hour.

Special discounts are offered to camera clubs and photo classes. Call for an appointment.