Originally posted by Swift1 This was more of a test shot than anything else.
I recently scored a FA 645 75/2.8 for a whopping $75. My mom has a 645N, so the lens went to her. Part of the reason it was cheap is because it has a nice deep scratch about 3/8" long in the front element. Other than that, it's perfect.
Anyway, we shot a test roll and as near I can tell the scratch has virtually no effect on IQ whatsoever.
It shouldn't unless light rays directly impinge upon the scratch, which will cause softening of contrast. There's an old astronomer and telescope maker trick for dealing with scratches on an element: india ink applied to the scratch only. It might look unslightly, but it solves the problem of loss of contrast. However, if you use a hood, you probably won't even have to worry about that.
As for any concerns about image degradation, there shouldn't be any, but here's a real simple way to prove it to yourself. Take a piece of string, and hold it against the front element of the lens, then look through the viewfinder. You can't see the string, can you? With a 75mm, you shouldn't even be able to see it with the lens stopped down to f//22. So, if you can't see something as big as a piece of string, then rest assured, your photos won't pick up that scratch.
About 25 years ago, I bought a very well used Nikkor AIs 180mm f/2.8 ED. Got it for really cheap because it had a large gouge out of the front element. It wasn't a chip, it was a for-real gouge. And that was one of the sharpest lenses I've ever owned. Took fantastic pictures. I sold it several years later during a time of too much gear and not enough money, but I still miss it.