Dust in lens & disturbing the glass

[F456]

Excuse my ignorance of lens construction. I know that dust gets into lenses as they are not air-tight; also that a bit of dust won't noticeably affect picture quality.

A recent secondhand lens purchase - Elmarit-M 2.8/28mm v.3 - is in great condition cosmetically and the aperture and focus adjust beautifully. There is a bit more dust inside than I am used to and while after testing I may be quite happy with the results, it set me wondering... Does dust removal entail tinkering with the position of the elements to get at them to clean them? I.e. does a lens service risk affecting the optical performance of the glass because its seating is somehow disturbed?

And a separate question: how often does a lens need focus-related adjustments? Is it usually the body that goes out of adjustment or can it be both/either? I hear of body/lens pairs being specially matched to ensure sharp focus,e especially with the Noctilux, 75mm Summilux and so on.

Thank you.

Tom

 

[Rob-F]

A little dust, or even a moderate amount, does little or nothing to harm image quality. I wouldn't take most lenses apart myself. It should be done by someone with an optical bench so as to check the lens after it has been re-assembled. I trust Sherry K., DAG, and John Van Stelten at "The Focal Point" with my lenses. These same techs are good choices for focus calibrations and matching critical lenses to the body they will be used with. The Noctilux and 75 Summilux are the most common candidates for this.

 

[Ko.Fe.]

I have to disassemble this lens after focus tab fell off at very first day after arrival...

I think, it should be some difference between DIY and service as paid service. At paid service they should know how to put lenses back exactly same way they were positioned on factory, lenses will be cleaned without adding of more dust and focus will be assembled spot on.

I didn't touched my 28 2.8 V3, optics. They are so tiny in so huge lens, it was difficult even see what is inside for me. And of course, I didn't assembled focus right, have to redo it.

I'm not touching lens glass if it is not 100% necessary. And to me it is only necessary if I need to stop fungus, get off oil reside or remove specks larger than dust. I never bothered with centering part, but getting flat and in correct orientation. Never have a problem on real world pictures. The only test I do after lens cleaning, assembly is checking it for focus accuracy.