Can someone tell me the best way to inspect a lens instore for fogging? This relates to the collapsible 50 Summicron I asked about a while ago. What else should I look for? Do a few cleaning marks really make a big difference?

-- David Killick (dalex@inet.net.nz), April 29, 2002

Answers

David,

Best way is to shine a torch thru it. Just holding it up to the light and looking thru is not enough. With a torch, if its fogged, it will become very apparent as a white cloud on the glass surfaces.

Minor scratches and slight fogging wont affect the image, but will def affect the resale value.

-- Karl Yik (karl.yik@dk.com), April 29, 2002.

Erwin Puts did a test which included both a collapsible with and without coating defects: http://www.imx.nl/photosite/leica/mseries/testm/scronhist.html
He concludes:
"The differences between the C with defects and the clean one are remarkably small. A drop in contrast, a higher level of flare and a loss of micro contrast when recording very fine details are visible. These differences might or might not be important depending on user-expectations and shooting circumstances."

-- Niels H. S. Nielsen (nhsn@ruc.dk), April 29, 2002.

Slightly OT, but I am always shocked at first when someone proposes shining "a torch" through a lens. It always takes me a moment to re- realize that you speakers of non-American English are talking about what we call a flashlight. To us, a "torch" is a long stick with a blazing fire at the end...hardly something you'd want near a Leica lens, even if it is supposed to withstand extremes of temperature;>)

-- Jay (infinitydt@aol.com), April 29, 2002.

Actually, Jay, the torch test is used to separate inferior plastic immitation lenses from real Leica lenses: the plastic ones burst into flame but the real Leica lenses just become incandescent. However, don't overdo it or you get some unintentional aspherical elements when the glass melts.

P.S. Just kidding - don't try this at home!

-- Ray Moth (ray_moth@yahoo.com), May 01, 2002.

For speakers of British English: "Olympic flashlight"? "I'm carrying a flashlight for you"?. Anyway, I tried the torch test. Didn't SEEM to be fogged, a few scratches on the front element, but the price - about $US150 seemed good. No-one here seems to ant old lenses, so I rescued it. How does that price compare?

-- Daivd Killick (dalex@inet.net.nz), May 02, 2002.

One thing to remember when doing the flashlight test is that the coatings on those old lenses aren't as effective as modern multicoatings, so even if the lens is in excellent shape, some degree of flare is normal. If there's haze or fungus, it's VERY obvious.

-- Mike Dixon (mike@mikedixonphotography.com), May 02, 2002.

Just the few scratches. Reading Erwin Putts you'd think the best place for those old lenses was the rubbish bin. I also have a Summar, and like it for portraits and landscapes. At smaller aperturs its quite sharp. But why do lenses have to always be razor sharp anyway!?

-- David Killick (dalex@inet.net.nz), May 02, 2002.