If you occasionally grow frustrated with the mental mistakes you make while taking photographs, you're not alone.

Take the professional photographer who, while attending a religious ceremony as a guest, was asked by the parents to take a couple of snapshots of their youngster in church. They lent him their camera, loaded with film and fitted with electronic flash. The pro walked around from one side of the church to the other, taking shots at just the right moment, just the right angle. All the while, the parents were confident the results would be first-rate.

When the film came back from processing, the family was devastated. It seems the pro had shot an entire roll of film with the camera set for electronic flash -- but without remembering to turn the flash unit on.

Then there's the case of the very well respected newspaper photographer who was assigned to get some photos at a nearby ski lodge. He went out in mid-afternoon on a bright, beautiful day. He used a Nikon camera with f/3.5 telephoto lens and 200 ASA film. It wasn't until about 4:30, though, that he saw just the shot he wanted -- a father and young son coming up the lift together. Positioning himself in just the perfect place for the best possible shot, he realized the sun had just ducked behind the horizon and his light meter read 1/30 second. And he's brought no flash. The resulting shot was a nice example of how not to take an action photo.

Another pro was disappointed and thoroughly puzzled when three rolls of film he took with a new rangefinder camera came back from processing blank -- totally unexposed.

The photographer took the camera back to the shop where he'd bought, and from there it was sent to the manufacturer's authorized repair center. Within three weeks, the camera was returned, along with a notation that repair personnel could find nothing whatsoever wrong with it. The photographer could hardly believe his eyes, but he took the new rangefinder and ran off several more rolls. This time, every roll was perfect.

The mystery of the three blank rolls might never have been solved if the pro hadn't gone shooting one day with a fellow photographer. As the pro zeroed in on a likely subject, she patiently pointed out to him that he'd neglected to remove the lens cap. Used to shooting a single-lens reflex camera, he'd just assumed that when he looked through the viewfinder's focusing window and saw his subject before him, the lens was uncovered. Sadly he learned otherwise.

Another pro, still, went to great trouble to shoot an on-location scene using hired models. It was a real rush job, with the prints due the client the following day. Shooting was outdoors in the dead of winter, with the temperature hovering near 20 below. Knowing he had limited time and not wanting to expose his equipment to the sub-zero weather any longer than necessary, he cut the session short -- just two rolls of 36 exposures each. He felt in his bones he'd gotten what he wanted on film.

The following day, the photographer had to cancel his scheduled meeting with the client -- and eat a $300 tab for modeling fees. It seems that, in the cold, he'd neglected to load the film properly. When he went to advance the film after each shot, he cocked the shutter and checked the film frame-counter, which advanced right on cue. But inside the camera, the film leader had slipped free, and the unexposed film just sat in its cassette. The results? Seventy-two frames of clear plastic.

Now, you're probably saying to yourself, I'll bet it's him he's talking about. I'll bet he's the yo-yo who pulled all those goofups. I'm not telling.