Dirt and grit in lens performance cost?

Hi all,

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I've been following this informative forum for awhile now and I have a question regarding M lenses and dirt. I just purchased a used 35 Summicron serial number 34xx xxxx and noticed that there is some dirt or grit on the surface of the lens directly behind the diaphram. On closer inspection, it seems as if some of the metal (or finish) from the diaphram has rubbed off the blades and deposited on the lens element. The diaphram seems fine but I want to know how this might affect performance of the lens. This is important to me because I regularily do 16X20 blow-ups of my work. Also, there seems to be a big piece of dust or flocking inside the rear element that is obscured by the diaphram blades at f2.8. Opinions?

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Thanks,

John, I don't see how these problems could do other than degrade the

lens performance, especially at f/2 where the flocking is exposed.

The 35 Summicron being one of Leica's finest lenses of all time, I

wouldn't be satisfied for it to be in less than top shape. It

should't cost too much to have that flocking removed, but I would

worry about damage to the surface of the element that's rubbing the

diaphragm. But you know what? The element behind the diaphragm of

the Summicron should have a concave surface facing the diaphragm.

This makes me wonder how the diaphragm could be rubbing the lens

surface, which, owing to its shape, ought to be safely recessed. I

have at times been deceived, when looking through the front element

of a lens, into thinking that I saw dirt on an internal element, but

on closer inspection it turned out that the dirt was on the rear

surface of the rear element, and easily cleaned. Is this possible in

your case? If the element is really compromised, I would want to

take it back.

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Regards,

Thanks Bob,

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What I meant to say was that the filings seemed to come from the

aperture blades rubbing together at f8-f16 (some of the finish is off

the blades). I doesn't seem like there is any damage to the element

behind the diaphram but you never know right? The lens mount is

screwed on and I wonder how hard it would be to get in there with

jeweler's screwdrivers, disassemble the lens, and blast the dirt out?

Anyone ever try this or is it a delicate task that you leave to the

Leica technician? It would be a handy skill because I'm probably

taking this lens to the Antarctic Circle where there are no Leica

techs. If not.... then how much would it cost to get the lens cleaned?

OK, sounds like the glass and coating might be all right, then. I

should think it would be worth it to have it cleaned. Now I am

wondering if what you are seeing might just be some residue of old

diaphragm lubricant. Looking at my 35mm Summicron (chrome, older 8-

element version) I do see three screws in the side, but I think you

will really need spanner wrenches to get the lens cells apart. One

slip--OUCH! Maybe leave it to a tech. Cost? I don't know, $100?

$125? Is there no possibility of getting whomever you bought it from

to cover the expense?

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Good Luck,

Send it out for a CLA if you are worried about it. My last CLA on a

50/2 was $80US. Only attempt the repair if you have experience

with small fiddly work and are willing to get the special tools (see

M2 top plate removal).

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Cheers

One or two small specks would be negligible in effect. Surface haze

from the break down of the lubricant in an older lens or moisture

could bring down contrast and affect overall performance by adding

flare. The rear element is more critical than the front being closest

to the film plane. An optical bench ( and expertise)is used to

calibrate the alignment of lens elements and I would not attempt the

diasassembly of a modern Leica or other lens. I agree that the 35

summicron starts out with pretty outstanding performance and could be

degraded considerably before becoming a problem.

Have you taken any test shots with the lens? Why not shoot a few at

various apertures and also in a back light situation and see how the

images look under the lube. If they are crisp and saturated without

any flare, shoot away. Otherwise, I like the work Bill Maxweell did

on cleaning up my lenses. It ran between $50 and $100 a piece

depending on the labor involved, and now the lenses are spotless

inside.