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Scratches on the Coatings? how does it affect image quality?
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PostPosted: Wed Jul 06, 2011 7:03 pm    Post subject: Scratches on the Coatings? how does it affect image quality? Reply with quote
Does someone has an example of scratched lenses vs non scratched, or an explanation of how in theory it would affect image quality of those lenses?


PostPosted: Wed Jul 06, 2011 7:26 pm    Post subject: Reply with quote
In a similar vein


PostPosted: Wed Jul 06, 2011 10:12 pm    Post subject: Reply with quote
http://www.mflenses.com/fs.php?sw=scratch

http://forum.mflenses.com/what-is-impact-picture-quality-if-a-lens-damaged-what-is-not-t8850,highlight,%2Bdamaged.html

less than 20 scratches not effect anything invisible on pictures, if there is lot of small cleaning marks , result is visible image has low contrast.
Even on wide angle lenses (ultra wide) some scratch not effect anything.

On rare side if you have big scratch it will be coming visible above F8.

I have several badly damaged lens I enjoy them , due silly buyers didn't take it and I go them for next to nothing. 35mm f1.4 Distagon Contax one of the most extreme example it has a few small scratches on front I bought for 200 EUR , another similar example is Nikon 20mm f2.8 AIS for 100 USD etc ,etc. Usually I sell MINT copies and keep scratched ones, need to care less and they are works really well.


But ... even if any people say thousand times scratches are not a big problem really , there will be thousand people (who never had scratched lenses) who are know very well scratches are ruin pictures ...
so I suggest to take an 5 USD lens take picture with that , scratch it take another one , sand it Wink and take another one and you will be a beleiver as I am scratched lenses are good as MINT ones.


PostPosted: Thu Jul 07, 2011 9:14 am    Post subject: Reply with quote
If scratches don't show on the image, I'd love to know what caused this:


This is on film, so I thought at first the negative was scratched, but I've looked with a loupe and there is nothing. It looks to me as though the scratches are highlighted by the sunlight, so that can't be a damaged neg.


PostPosted: Thu Jul 07, 2011 9:33 am    Post subject: Reply with quote
It might, of course, be the enlarger lens ? My other thought, and I'm not joking, is a spider's web!


PostPosted: Thu Jul 07, 2011 9:48 am    Post subject: Reply with quote
martyn_bannister wrote:
It might, of course, be the enlarger lens ? My other thought, and I'm not joking, is a spider's web!


Yes, and I see 2 spiders too Very Happy

Scratched lens coating is not a big problem for IQ IMO, but a scratched back element could be really bad for IQ.


PostPosted: Thu Jul 07, 2011 10:37 am    Post subject: Reply with quote
Ask a friend to borrow you his glasses. They must be few years old though. I think you'll get the idea. Mine are around ten years old. MC is very scratched but i am so used to them Smile.


PostPosted: Thu Jul 07, 2011 11:49 am    Post subject: Reply with quote
peterqd wrote:
If scratches don't show on the image, I'd love to know what caused this:


This is on film, so I thought at first the negative was scratched, but I've looked with a loupe and there is nothing. It looks to me as though the scratches are highlighted by the sunlight, so that can't be a damaged neg.


I'd guess it was the enlarger's glass that was scratched (if used, of course).


PostPosted: Thu Jul 07, 2011 12:36 pm    Post subject: Reply with quote
I'll vote for a spiderweb catching the sun.


PostPosted: Thu Jul 07, 2011 1:08 pm    Post subject: Reply with quote
Not an enlarger, it's a slide not a neg, sorry. It could be the scanner, although I would have expected it to reflect blue scanner light, not golden sun. I'll try scanning it again.

I doubt it's a spider's web. Looking closely at the lines I've never seen a web like that, And there was nothing nearby to which a web could have been attached.


PostPosted: Thu Jul 07, 2011 4:05 pm    Post subject: Reply with quote
When I said spiders web, I meant as in gossamer. But you are probably right, it's on the lens.


PostPosted: Thu Jul 07, 2011 4:08 pm    Post subject: Reply with quote
is it possible to see the whole image at a large size?
(you can paint faces black if privacy's a concern)


PostPosted: Thu Jul 07, 2011 4:35 pm    Post subject: Reply with quote
Orio wrote:
is it possible to see the whole image at a large size?
(you can paint faces black if privacy's a concern)

Hello Orio, I cropped the pic to enlarge the scratches, privacy wasn't a concern. I'm also posting the next pic on the roll - if there were any scratches they would be on the left side. I don't see any but the light angle is different. Pentax P30n with M 1.7/50 on Provia 100F





PostPosted: Thu Jul 07, 2011 5:04 pm    Post subject: Reply with quote
Seeing the whole image makes me lean towards something in the processing/scanning. I don't know exactly what, but notice the debris I have higlighted



PostPosted: Thu Jul 07, 2011 5:43 pm    Post subject: Reply with quote
martyn_bannister wrote:
Seeing the whole image makes me lean towards something in the processing/scanning. I don't know exactly what, but notice the debris I have higlighted

Yes, you're perfectly correct there Martyn. Even though I clean the scanner glass every time and I dust the sllides with a very soft brush, I still get this amount of debris showing up, or even more sometimes! Both pictures I posted are the raw scans, I've been over them with the clone stamp for the album copies.

The transparency unit lamp in the Epson V700 scanner has a strong blue colour, and I don't think the golden colour of the scratches could have come from that source. However, I've remembered there's another warmer lamp under the platen that's more likely to be the culprit. I'm going to dig the slide out later and scan it again.


PostPosted: Thu Jul 07, 2011 9:11 pm    Post subject: Reply with quote
Considering the apparent focal lenght and aperture, I would say that the chances that those scratches are coming from the lens surface are nearly zero.
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