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12-18-2013, 09:24 PM   #1
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testing a lens for impact of scratches on coating

I just bought a new lens off e-bay, advertised as being in EX+ condition. Needless to say, it was not in that condition (or else why would I be posting here). There are a couple of what appear to be scratches in the lens coating, one of which looks to be over half an inch. I don't see them when I look at the lens from the front, but do see them when I look through the lens from the mount side, and only in certain light. My question is what is the most effective way to test the lens to see if the defects affect the image quality. Specifically, what aperture, etc. The lens is a 200mm f4. As always, i appreciate the input.

12-18-2013, 09:29 PM   #2
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You'll never see the effects of the scratches. At worst, they'll cause a nearly immeasurable loss of contrast.

While the eBay seller shouldn't have been advertising a lens as EX+ without perfect glass, I really wouldn't worry about some barely visible scratches.

Oh, take a look at this (it's relevant to your question):

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/231454-guess-lens.html
12-18-2013, 09:32 PM   #3
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It likely will not affect anything except when you are shooting into a light source.

There is a post (I think the last post in the link above) showing images from lenses with severe front element damage. It took a lot of damage to be noticeable.
12-18-2013, 10:03 PM   #4
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You might be refering to this one: LensRentals.com - Front Element Scratches

12-18-2013, 11:48 PM   #5
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QuoteOriginally posted by toukan Quote
There are a couple of what appear to be scratches in the lens coating, one of which looks to be over half an inch.
Front or rear? If on the rear element, they may impact image quality. In any case, a lens with visible scratches on the optics is not E+ or even E-.

Is it safe to assume that this is a Pentax-M 200/4 or the almost identical XR Rikenon 200/4? If you paid a premium price (more than $45 USD), I would suggest a frank discussion with the seller. If you paid $30 USD or less and the scratches are on the front element, I would say "no harm, no foul" and just leave neutral feedback with appropriate comments if an eBay transaction. If the scratches are on the rear or internal elements (evidence of botched cleaning to remove fungus), I would suggest that full refund might be in order regardless of price paid.


Steve
12-19-2013, 10:21 PM   #6
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Thank you for your replies. Actually, it is a Yashica DX 200/F4. It appears the scratch is on the front element, based on how it comes into focus when turning the focus ring. And for the record, it was $30 (plus s+h). Gonna try it out this weekend. I will report back then.
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