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12-15-2009, 09:02 PM   #1
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Stupid Noob lens question.

I am new to the dslr world and I have been perusing the used market on lenses and I see alot of reference to 'oil free blades', my question is what is the concern with non 'oil free blades'... could some please enlighten me.

Thanks

12-15-2009, 09:38 PM   #2
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QuoteOriginally posted by bob_00 Quote
I am new to the dslr world and I have been perusing the used market on lenses and I see alot of reference to 'oil free blades', my question is what is the concern with non 'oil free blades'... could some please enlighten me.

Thanks
Honestly, this seems more like a smart noob question to me ... I will say the most noobish thing about it is the title of the thread - you'd be more likely to get a lot of quick help with a better thread title like, "What are oily blades?" or similar...

Alright, on with the answer... the blades in question are the aperture blades in the lenses diaphragm (more often called the aperture). The diaphragm controls how much light comes through the lens, and has some other effects on the image (depth of field is changed at different aperture settings), but the diaphragm is left "open" when you are preparing to take a picture (while focusing and composing, etc...) and only "stops down" momentarily when the shot is fired. If the lens has had a hard life, oil from the grease inside the lens (I think often the zooming and focusing mechanisms will have some lubricating grease), can run onto the aperture blades and mechanism and cause the blades to stick or move very slowly - this keeps the aperture from functioning correctly, and will mess up your exposures. Essentially, a lens which this has happened to is broken, and repair will be necessary for the lens to work properly.
12-15-2009, 10:23 PM   #3
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Just to add to Josh's post: with a typical K-mount lens, the aperture blades are fully open until you press the shutter button, to make framing and focusing easier. Then they close to the aperture you chose to take the photo. They have to move pretty fast to do this, so they are very lightweight, thin pieces of metal. You'd think oil would help, but the blades stick together with any liquid on them at all. The rest of the mechanism appears to be designed to operate without oil either.

The oil sometimes comes from grease in the focusing mechanism. If the lens is left in a hot car, it can vaporize the grease, and it gets deposited on the aperture blades and everything else. The better manufacturers use grease that doesn't vaporize easily, so their lenses have fewer problems.

The problem is not that hard to fix, if you can get to the aperture blades. But the blades are right in the middle of everything, so getting to them might involve a lot of work. The blades are cleaned with solvent. I have learned to clean the inner lens surfaces and interior at the same time.

For screw-mount lenses on non-screw-mount cameras, the aperture doesn't need to work that fast, so a slightly oily aperture isn't a big deal, except the resale value plummets. The oil may eventually make the aperture too slow. Some Russian lenses are designed to work with oily blades. Sellers will typically point out that it's not a defect for that lens. Auto-focus lenses have little or no focus grease, so they are less likely to have that grease migrate to the blades, but it's not impossible.
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