Checcking a lens for scratches

[RaglanSurf]

Morning all,

What's the best way for checking a lens for scratches?

What I mean is, if the lens has an obvious scratch what's the best subject/background to photograph to see whether the scratch is visible in the final image?

Also should the lens be de-focussed and should the aperture be as wide as possible or as small as possible?

Thanks

Oh and it's on a film camera so I can't just go blasting away at all settings just to check

 

[cuthbert]

if you can't see anything on the front element by examining it in good light then i very much doubt there is anything there.

i guess you take the lens off the camera, remove both endcaps and look through it to see if there are any scratches ?

 

[RaglanSurf]

It's not seeing the scratches on the glass that I'm having the problem with it's how those scratches affect the final image, how obvious they are or aren't. And what's the best way to assess those scratches eg do I de-focus and point the camera at the sky or focus on a plain white wall? That kind of thing.

 

[cuthbert]

well, the only way you'll truly be able to do that is if you have two identical lenses, one with scratches, one without and take a picture of the same thing, with the same settings on the same camera.

minor scratches on the front element of a lens will usually have no visible affect on picture quality, other than perhaps added flare and a minor loss of contrast.

this one comes up from time to time and will hopefully put your mind at ease:

http://www.lensrentals.com/news/2008.10.30/front-element-scratches

 

[Mostly Vintage Cameras]

Look down one end of the lens and shine a torch up the other, then look down the other end and repeat. You’ll be amazed how “bad” lenses look!

The reality is scratches won’t effect your ‘photos with the only exception being the possibility of increased lens flare if you have a really big scratch on the front, in which case use a lens hood!

 

[jim_j]

Someone also mentioned using a black felt tip on the scratch, which apparently helps counteract possible flare from the scrtatch.