Testing severity of scratches

[Digitally Pleasing]

Hi Everyone,

So I just bought a used Tamron lens off ebay and it arrived today. While inspecting it, I noticed there is a very very small scratch on the lens... it is tiny.

I doubt it is big enough to effect the picture, but is there a proper way to test this? If I set up some lights in a particular way will I notice the scratch more so?

I did a very quick test with available light in my apartment and didnt see anything, but I just want to be sure.

Thanks

~ Jim

Update: I just looked over a bunch of stills and video. Both look fine. It got me thinking though, how big of a scratch does there need to be for it to be noticeable?

 

[Michael Olsen]

In my opinion, it would be a bit hard to tell without having another version of the same lens that was in pristine condition.

Surprisingly, scratches usually don't show up as a specific "trouble spot" within the lens. There isn't some small portion of image that just looks incredibly messed up.

Instead, scratches usually result in a general loss in contrast of the image, as well as the resolution. They may also contribute to flaring.

How big does it have to be to be noticeable? I'd say that's a very variable question depending on the size of the elements, the resolution of the lens in the first place, the resolution of the recording medium, the contrast and composition of the scene itself, etc.

In short - if it looks good to you, it probably is. Have fun!

 

[dvollrath]

I agree with Michael. It sounds like your lens is fine.

Sometimes you can notice a scratch directly. One way to do try to do it is to shine light directly into the lens and focus the lens at its shortest distance and maybe stop it down a bit too.