PBase

Hi
I'm noticing that I'm getting scratches along the length of my slides. I don't think they're on every slide although I can only really see them clearly when there is a plain image on the slide ( clear sky for example).

I'd like to find out for sure if it's happening in the camera or at the lab.

Am I right in thinking that after making sure the camera is clean I could run a film though the camera and then immediately examine it for scratch marks. I know I'd ruin a perfectly decent fim doing this but at least I'd know if any marks did appear on the film surface it would definitely be happening in the camera.

You could do that. Most scratches occur on the film base side, usually due to dirt, chips, or scratches on the pressure plate (or less frequently, dirt in the film take-up chamber where the film winds inside out). Scratches on the base will probably be easier to see than scratches on the emulsion since the base is smooth (best to use a loupe while checking). I'd leave the last two or three frames "unexposed" in the canister for comparison.

Before cleaning the camera, I'd run my finger on the pressure plate to feel for any imperfections. Also look for clues from the position of the past scratches - are they in the same place, are they completely straight, etc.

many thanks for the tips

You can quickly rule the lab in/out.

Shoot a couple of 24 exp rolls of cheap print film and drop them off at two different one hour places.