Loading a 35 mm camera is easy. However, it is possible to put a 35 mm magazine into the camera the wrong way. The film slot of the magazine must face the take-up side of the camera; and the light-colored side of the film, the emulsion side, must face the camera lens. If the following loading summaries differ from the instructions in your camera manual, follow your manual.

With an auto-loading camera, line the end of the film leader up to an index mark along the bottom rail. Check that the advance gear engages the film perforations and that the film lies flat.
Close the back and press the shutter release. The camera will advance the film to the first frame.

Film in 35 mm magazines is loaded in lengths for 12, 24, or 36 exposures. (A half-frame camera yields twice as many exposures on the roll.) Extra film is included for a leader at the beginning of the roll and for a trailer at the end. The processing laboratory needs the leader as well as the trailer when processing the film. If you try to squeeze more than 24 exposures (or 12 or 36 depending on the roll) onto a roll of film, the extras may be lost in the processing.
Electrical contacts in the film chamber enable many cameras to read DX-encoded films to automatically set film speed, determine the number of exposures on a roll, and the exposure latitude of the film.
How do you know if the film is advancing? Auto-loading cameras often have a film-running indicator atop the camera to indicate film is advancing. With a manual-loading camera, you can use the rewind knob to check the film. Turn the rewind knob carefully in the direction of the rewind arrow until you feel a slight tension. This takes up the slack in the film. Now when you advance the film, you should see the rewind knob rotate.

CAUTION: Be sure that you never turn the rewind knob the wrong way-opposite the direction for rewinding-when taking up the slack in the film. This could kink or jam the film. After you load the film, it's easy to forget how many exposures are in the magazine. Many cameras offer a window on the film door that lets you see the part of the film magazine that indicates the number of exposures. Other cameras have a memo holder on the film door into which you can insert the end flap of the film package; the end flap states the type of film and how many exposures. With a manual-advancing camera, if you think you have 36 exposures but actually have 24, you could damage the film by tearing the perforations or you could pull the film loose from the magazine by trying to advance the film. If you pull the film loose, you can't rewind it back into the magazine.

With older cameras, it's sometimes difficult to tell whether the camera is loaded with film or not. If the film counter indicates an exposure number, there's probably film in the camera. With a manual-advancing camera, gently turn the rewind knob in the direction for rewinding without depressing the rewind button. If you feel resistance to turning the rewind knob, do not turn it any farther. Your camera is loaded with film. The film counter in most 35 mm cameras has an S on it that resets when you open the back. If you see the S on the counter, this indicates that the camera back has been opened since the last exposure was made. Therefore, it's safe to open the back again.

With most 35 mm cameras, you must rewind the film from the camera take-up spool back into the original magazine before unloading. If you open the camera back before rewinding the film, the film will be completely exposed, or fogged, as it has no protection from the light. Fogging generally looks like a light, cloudy area covering part or all of a slide or print.

Cameras that load film automatically, usually also rewind it automatically. The camera may automatically rewind the film at the end of the roll, or it may signal you to press a rewind button or switch that begins the rewind. Check your camera manual for specific instructions.

Because auto-load cameras require you to expose less leader film when loading, it is possible that you'll get more than the specified number of exposures on a given roll. But again, be aware that any shots past the specified number of exposures (i.e. 12, 24, or 36) may be lost in processing.

IMPORTANT: When using a camera with a manual rewind knob, do not turn the rewind knob in the direction opposite that of the rewind arrow. Such action can seriously bend the film and possibly tear it. To prevent torn perforations, keep the rewind button control firmly depressed in the rewind position until you have completely rewound the film. Check you camera manual for specific instructions.

If you don't force the film advance lever, you won't pull the film loose from the magazine, which would prevent the normal rewinding of the film back into the magazine, as mentioned before. Pulling the film loose usually results from a photographer trying to make more exposures than 24 on a 24-exposure roll (or 12 or 36 depending on the roll) at the end of the film. Forcing the film advance lever can also cause overlapping pictures at the end of the roll. If you do pull the film loose from the magazine and open the camera back in the light, you'll fog the film. The solution is to take your camera to your photo dealer and ask to have the film transferred in a darkroom into a KODAK SNAP-CAP 135 Magazine. It is important to mark the film type and number of exposures on the magazine so that the processor can identify the film.

Each year several thousand magazines of 35 mm film are returned for processing by photographers who have accidentally wound unexposed film back into the magazine. The most common reason for this happening is improper loading of 35 mm cameras which can cause the film not to advance through the camera as pictures are taken. After the photographer finishes what is thought to be the end of the roll, the film is rewound. Since the film didn't even go through the camera, no exposures were made and all the pictures are lost. Needless to say, this is a big disappointment.

To minimize the chances of winding the film leader into an unexposed magazine, load your camera according to the instructions in your camera manual. Also follow the tips given in this book about determining whether your film is advancing properly.
When a film's leader is completely rewound into the magazine, it most often signifies that the film has already been exposed and, therefore, needs to be processed. You should contact a photo retailer or photofinisher in your area for their service. If there is any possibility that the film was used or mixed with films used to take pictures, you'll want to have it processed.

It is possible to retrieve film leader from 35 mm magazines so that the film can be loaded in a camera. However, our research shows that in such cases the risk of double exposure is great. It would be extremely disappointing to re-use the film and lose both sets of images. There are instances in which auto-advance/rewind cameras rewind film into the magazine before reaching the end of the roll; a phenomenon called "premature rewind". The major causes of premature rewind are film-loading and camera-operating mishaps.