Does anyone have any proven examples of cleaning marks causing loss of contrast?

darinwc · Jan 31, 2007

Does anyone have any proven examples of cleaning marks causing loss of contrast?

-I have a couple of lenses with so-called 'cleaning marks'. Tiny scratches visible only when shining a light through the lens. Some people say not to worry, but does anyone have any examples or tests that show a marked difference?

Ole · Jan 31, 2007

Not even I have two otherwise identical lenses, one with and one without cleaning marks.

I have two identical lenses with different contrast, but one is coated and the other one is uncoated and has a big chip in the front element. I'm not even sure the chip contributes much to the reduced contrast - eight glass/air surfaces is bad enough!

Steve Hamley · Jan 31, 2007

I doubt you'll find anyone with two identical lenses, one perfect and the other not - you usually sell or tade the imperfect one just on general principles.

But I do have a few lenses with minor cleaning marks, including a 8-1/4" Gold Dagor with a few. I bought these from a local pro who made his living with them for many years, so I doubt there's much effect from cleaning marks unless you can look through the lens at a light source and see them or flare from them with your eye. That's my test.

Of course, you should always use a lens shade to keep contrast up, cleaning marks or not. You do always use a lens shade before worrying about cleaning marks don't you?

Steve

phfitz · Jan 31, 2007

darinwc,

"Does anyone have any proven examples of cleaning marks causing loss of contrast?"

I do have two identical lenses that fit the bill but I never thought to bother testing them against each other. Maybe I can make some time this weekend, 2up on 5x7 so everything else is the same.

high end lenses years ago had air-bells in the glass and they made no different so I doubt a cleaning wipe would change anything but the price. Greasy thumb prints WILL make a difference though.

PhotoJim · Jan 31, 2007

The difference will be there. It may be subtle, but if you have enough backlighting you will be able to measure a difference in contrast. Most such differences can be corrected in the printing stage so it's seldom an issue, but it's still real.

Even those bubbles make a difference. Anything less than perfection makes a difference. The question is whether the difference is enough to matter, and I agree that often it does not.

The test will be interesting, but I bet that if the marks are significant enough, a difference will be appreciable. It may take serious backlighting to invoke it, but it will happen, I'm confident.

If the coating didn't matter, manufacturers wouldn't waste their money coating lenses, after all.

JG Motamedi · Jan 31, 2007

I have seen and tested for a difference, but can't prove it to you as I don't have access to the test sheets.

The test subject was two 210mm f9 Schneider G-Clarons of approximately the same age, one had a really messed-up coating on the rear element (looked like somebody tried to remove it with fine grit sandpaper) and the other was more or less free of coating flaws.

The result was pretty obvious--in any circumstance in which a lens could flare, the damaged one did. Aside from flare, the resolution seemed also to suffer, although it was difficult to tell since the flare was so bad.

Jim Jones · Jan 31, 2007

I replaced a 50mm Summicron because of many years accumulation of cleaning marks. A 203mm Ektar also has the same problem. Flare in the shadows is the worst problem with both lenses. For much photography their performance is still good.

fpjohn · Jan 31, 2007

Hello:

I have a 65mm f4.5 Grandagon which seems to have been cleaned with a Brillo tm pad (this is why I could afford it). Patches of the coating are gone on both rear and front elements. Images appear tack sharp. If anyone wants to lend me a pristine version, I'm willing to do a comparison test in flare prone conditions .

yours
Frank

DBP · Jan 31, 2007

I have a pair of Jupiter 3s (50/1.5 - LTM) with severe cleaning marks (look almost like cobwebs) and while I have not formally tested them against the one I have without marks, I can tell you that the loss of contrast is easily noticeable even at 4x6. I would not worry about one or two marks, especially given how forgiving LF is, but I would worry if the marks were as bad as my Jupiter 3s.

Ole · Jan 31, 2007

Ehrm yes - I was suddenly reminded of my little stash of FEDs, IN-22's, and IN-50's. All 50mm f:3.5, all with varying degrees of cleaning marks from "hardly visible" to "coarse grit".

I could test that, instead of just using the best one...

DBP · Jan 31, 2007

Ole said:
Ehrm yes - I was suddenly reminded of my little stash of FEDs, IN-22's, and IN-50's. All 50mm f:3.5, all with varying degrees of cleaning marks from "hardly visible" to "coarse grit".

I could test that, instead of just using the best one...

Did the Soviets really issue 200 grit lens paper?

Ole · Jan 31, 2007

I believe it was more like 60 grit, judging by some of my lenses...

Ray Heath · Jan 31, 2007

darinwc said:
Does anyone have any proven examples of cleaning marks causing loss of contrast?

-I have a couple of lenses with so-called 'cleaning marks'. Tiny scratches visible only when shining a light through the lens. Some people say not to worry, but does anyone have any examples or tests that show a marked difference?

g'day darin
you're sure to get contradictory answers to such a question, so why not make your own images of the type you normally make and assess the results for yourself

my experience is that to a certain amount they have no discernible affect, and any affect will be variable with the aperture used

Jim Jones · Jan 31, 2007

Ole said:
I believe it was more like 60 grit, judging by some of my lenses...

60 grit for lenses, 200 grit for toilet paper.

darinwc · Jan 31, 2007

would the differences be more noticable with a wide aperture or stopped way down?

Ray Heath · Feb 1, 2007

darinwc said:
would the differences be more noticable with a wide aperture or stopped way down?

stopped way down, if at all discernible, which i doubt

Scott Peters · Feb 1, 2007

I own a 24" artar with very heavy cleaning marks...it is coated. It works fine. I use a lens shade and if very concerned about contrast, I use a filter (yellow, yellow green, orange) to perhaps 'get a little more' contrast. Honestly, I have more variability/issues with contrast in metering, developing and printing, such that this lens with heavy marks isn't an issue. Funny thing is, it's sharp as a tack! It's crazy because I look through the lens with my eye and it even looks hazy...go figure. FYI I stop down a lot and contact print, so YMMV.

jimgalli · Feb 1, 2007

Think in terms of percentages. A lens with a nasty cleaning sleak or sleaks has lost what? .008% of it's reflected surface? It lost 40% of it's value for that .008% performance loss and me being a tightwad.......well.......all I wanted to do was make pictures so I'm attracted to the slightly less than perfect ones. I took an old Bausch & Lomb lantern lens apart the other night to soak the elements in some detergent for a few hours. One of the very thin elements slipped and fell against the porcelain and iron sink and broke a chip out about as big as half a fingernail. I painted that area black and re-assembled. All I can say is it's still stunningly contrasty for it's design and age. Worthless. It falls under rule 8 on your other list.

Does anyone have any proven examples of cleaning marks causing loss of contrast?

darinwc

Ole

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phfitz

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Ole

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Ole

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darinwc

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jimgalli

Does anyone have any proven examples of cleaning marks causing loss of contrast?

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