Q. A friend told me that cameras were getting so fancy that you not only don't have to set the exposure to take a picture, you don't even have to set the film speed anymore. How can a camera know what the film speed is? How automatic can you get?

Q. What are all the new markings on the film cans? Is this an effort at modern art?

A. What we're talking about here is DX.

This is the system introduced by Eastman Kodak in 1983. The film cartridge or film bear four codes and a one-line film ID, many of which make the automatic cameras even more so.

* The code that will affect your picture-taking the most, is the Camera Auto Sensing (CAS) code. That's the pattern of up to 12 squares of bare metal and black insulation on the cartridge. Probes inside the camera press up against these squares and become a circuit board that tells the camera certain things:

Squares two through six indicate film speed in 24 divisions from ISO 25 to ISO 5,000! Squares eight, nine and 10 tell the number of exposures, and squares 11 and 12 show the exposure range of the film. Squares one and seven are electrical contacts.

Before we go any further, let's understand, please, that this doesn't work on all cameras. Most of the newer cameras are equipped to work with DX. Most of the older ones are not.

The popularity of the DX system is growing rapidly. More and more manufacturers are producing cameras made with CAS probes and film ID windows. (Some of these are the Pentax PC-35 AF-M; the Nikon One-Touch and Nikon N-2000; the Minolta Maxxum 7000 and 9000).

Most major film companies such as Agfa, Fuji, Konica and 3M now have DX or plan to have it very soon.

What does it all mean? The CAS function is obvious. No more discovering that you've shot the entire roll at the wrong ISO setting. Now, it's just load and shoot, knowing that the ISO is slected for you and is correct.

That's fine for most shooters, but those who want to deliberately overrate slides or underrate Tri-X have problems. Some cameras will allow you to override the DX code; if not, things get complicated.

The other tricks of the CAS squares may not seem as important as the film-speed setting, but they are neat gimmicks. The exposure counting aspect is good for the cameras that re-wind automatically; it gives you a truer count of what's really left on your spool.

The film range information can permit the taking of a picture even when the automatic camera signals an improper exposure. If the film has a wide enough range, you'll get an exposure, albeit a poor one.

* On the opposite side of the cartridge from the CAS squares is a film ID. This is placed so that it can be seen through a small window in the camera. With it there's no more sticking a box top to the back of your camera to remind yourself what you've loaded.

The two other codes on the DX cartridge are for use in processing.

* The bar code that looks like the universal product code used in the supermarkets and the series of up to 12 holes in the film's leader. They help guide the film into the correct solutions and show the length of the film respectively.

Finally, there is a latent image code, printed at regular intervals along the film, which identifies it during printing for automatic color balance.

Whew! Being simple sure gets complicated.

This is all part of the pell-mell rush toward total automation. The time is fast approaching when all of the photographer's time can be spent in thinking only about his picture. The camera will do the rest.