Q. I tried to take some pictures at outdoor performances, specifically of the fireworks at the end of the program. I was prevented by one of the ushers who said "no pictures." How come? I'm mad and I'm not going to put up with this.

A. I wouldn't either. It's about time photographers complained about this arbitrary "no pictures" role at outdoor public events. I think as long as you're taking a personal picture and not disturbing others with flashes, by standing up or incessantly clicking, you have every right to take a picture. After all, photographers are no longer using flash powder and heavy tripods but modern ubobstrusive equipment. I asked a theater manager about the "no picture" rule and was told this is a stagelands' union ruling and that there is an "official photographer" who will take a picture for you at a price. This doesn't make sense. I don't think that any group should dictate whether you can or cannot take picture and I certainly would want my own photos, not somebody else's.

Q. What is a "normal" focal length for a cameras lens?

A. It all depends on the size of the film area convered. In each case it is equivalent to or close to the diagonal of the film size. I or example: the normal focal length of a lens on a 35 mm camera is 50 mm.

Q. Will the new Pentax ME model due to come out in the spring accept universal screw-mount lenses?

A. My information is that you will be able to use an adapter for screw-mount lenses, but that with the adapter, the lenses will not be automatic.

Q. I am taking a photography course and I want to be a professional photographer. What is a good way for an amateaur to start selling photographs to magazines?

A. First, study the magazines to see what kind of subjects they use and the style of their photography. After choosing your market, find a suitable subject and shoot a series of photos within the magazine's format, but with your originality. But sure to send a complete caption information and story outline with your material, as well as return postage.

Q. I bought an Olympus OM 1, which I just love. I'd like to get a wide-angle lens. What focal length would you recommend?

A. My suggestion would be a 21mm for an all-around wide-angle. However, Olympus has a wide assortment from 8mm fisheye and up. If you have a particular need, it's best to try various focal lengths in the store before you buy, and to imagine the use to which each would be put.

Q. I have some good shots that I would like to mount at the wall as transparencies. How can I do this?

A. The transperencies can be mounted between two pieces of plastic, clear in front and translucent in back, in a shadowbox frame, which can be illuminated by fluorescent tubes. You can determine the depth of the frame by trial, before assembly, by shining the light on a piece of white paper and moving the mounted transparency back and forth until the light is reflected evenly through the entire image.

Q. I got bad shadows above the heads of my subjects, even though the flash is mounted above my camera. What's wrong?

A. Your camera level is below the eye level of your subjects so the flash casts a shadow above the heads on the background. One cure for this is a higher camera angle or holding the flash off and above the camera.

Q. Can I have the new professional Ektachrome film pushed by the lab?

A. Yes. In the next three to four months Eastman promises to pust to ASA 400 on request. They also say that the new TL 200 can safely be pushed to ASA 800.

Q. I hear the Ektachrome E3 process will be discontinued. When?

A. Any day now. Stores may still carry what they have in stock but they won't be restocked.

Q. What's the "aim point" in color film manufacture?

A. The aim point is a circle of plus or minus 500 correction that falls on the intersection of the magenta, red, yellow and blue, cyan and green. Color film balance should fall within this tolerance or "aim point."