I was given a lens from a friend because it has a tiny scratch on it.
It's a Tamron 24-70 f2.8 and playing around with it, it seems like a really nice lens.
I've shot some test stills and video, and for the life of me, I can't see the scratch in the images.
Is there a way to test to see if the scratch is noticeable, ie, if it's zoomed all the way out with an open aperture, etc etc - because, for the life of me, I can't think why I shouldn't use the lens even with the tiny scratch.
Depending on the scratch you'll notice it more when near-focused and if it is deep enough to cause light refraction- typically if a light source is visible to the lens (like the effect of using an (x)-point star filter yet far less flattering or desired).
If it is minor enough you should be able to get away with it never being noticed in your footage. Only way to know for sure is to do some tests. Roll on some footage and pan/scan/tilt your camera on objects close to lens and also on distant objects - lock off the camera and roll on a face as the subject's head turns and looks up/down - the throw up the resulting footage on your monitor and study the area on the screen where the scratch would be - notice anything? look for a slight softening around that spot or along the scratch line. Also try beaming a flashlight around the lens as you are rolling - see any light streaks on the scratch when you play back the footage?
Still photographers can get away with more in situations like this as any distortion created by the scratch will be less noticeable on a still than with moving footage. But if the scratch is superficial enough you can get away with it for video as well… Just do your tests to make sure you don't end up with an ugly soft spot over an interviewees eye or a weird light-streak while tracking an object.