Q. I have a Minolta Maxxum 9000 with a Program Back Super 90. Recently I bought a motor drive MD-90.

I shot a roll of the new Ektar ISO 25 print film, mostly indoors with flash. The roll contained pictures that have several red straight horizontal lines. I believe that the data imprinting source has caused these lines.

Can this be true? What else may be at fault: the speed of the film, the flash, the motor drive?

A. Those lines are probably being caused by the interaction of the data back and the slow film.

It's taking the data back more time to expose information onto the film because of the slow ISO, more time than it takes for the motor drive to advance the film.

Therefore, as the film advances, the data back is still working and causing those red streaks.

You can solve this by going to a faster film, or setting your ISO at 50 and using a +1 exposure compensation.

Q. I have two questions about the Minolta Maxxum 7000 I have owned for about four years. I'm really very happy with it; it works well and I haven't had any problems to speak of.

It has, however, been to the beach, on a boat and in a number of other places where it might have gotten dirty. Should I have the camera professionally cleaned or serviced, and if so, how frequently and what should be done?

Second question: On a recent trip I was using Kodak ISO 100 print film to take mostly outdoor shots. A few were made indoors. These were, for the most part, taken in a pretty dark room, but I have a good bounce flash.

Some of these indoor shots came back from processing with what looked like a thin, opaque milky film over them. What caused that and what can be done if you have to take pictures in a dark place that cannot be lit better?

A. First, if it's not broke, don't fix it. But, there are some common sense things you can do yourself.

When you are taking pictures at the beach, or any other sandy or unpaved area, you must be extremely careful. When you change film, for instance, make sure your hands are clean and dry. Shelter your camera from wind gusts that could bring tiny particles to your camera, cause scratches and eventually foul up the working parts.

I like to carry a small brush-blower for times like these and make sure I clean the back of the camera well during reloading. A word of warning: don't remove the lens and try to clean the mirror or the front side of the camera. They are not designed for field cleaning, and need a professional's touch and tools.

If for any reason you suspect that the camera has been splashed on, or if you hear any strange noises, it should be looked at by an experienced repairman immediately.

About that milky cast to your pictures: I have only seen this on color prints once, and the probable cause was traced to underexposure.

In your case, I would try some shots in dark rooms, but use direct flash instead of bounce flash. Dark rooms often have dark ceilings and walls, or very high ceilings -- the things that can make bounce flash ineffective.

Also, be sure that you are within the range of your flash. If you're too far away, underexposure results.

One other thing: Have the batteries on your flash been changed lately?

THE SECOND HALF of the photo contest sponsored by the Friends of the National Arboretum is underway. The contest's theme is "An Arboretum for All Seasons." Pictures must be taken at the arboretum during two seasonal time frames: summer (June 22-Sept. 21) and autumn (Sept. 22-Dec. 20). The contest is open to both amateur and professional photographers, but their work will be judged separately. Color slides and color prints will also be judged separately.

Judging will be in December. For all the rules, prizes and entry forms, call the Friends' office at 544-8733.

FEEDBACK: A couple of readers have supplied answers about processing that old Kodak color film that needs handling in C-22 chemistry.

Readers from Kodalux Processing Services recommended two labs: Qualex, Inc. at 616 Dwight Street, Springfield, MA 01101; and Rocky Mountain Film Lab, 145 Madison St., Denver, CO 80206.

Another wrote, "This film can be sent to Kolor Print, 2121 Thayer St., Little Rock, AR 72202. Send $10 with the film and this lab will process any old film a person has, and return the finished product -- good, bad, or indifferent -- in about 10 days. I did the same thing with the same kind of film."

SORRY, WRONG NUMBER: The telephone number for ordering the video tape "150 Years of Photography" was incorrect in this column last week. The correct number is 800/521-2666.

Write Carl Kramer c/o Weekend, The Washington Post, 1150 15th St. NW, Washington, DC 20071.