Oil on the aperture diafragma blades = really bad ?

[vicmortelmans]

Oil on the aperture diafragma blades = bad ?

I recently got a Jupiter 9 (from ebay). It is a M42-mounted lens for my Pentax SLR's, but I think the issue is independent of camera type. It's in overall very good condition and also very clean on the inside, but it has (a lot of) oil on the blades.

It's always mentioned as a *bad* thing, but I wonder why. I can see two reasons:

1. the oil may spread onto lens elements

2. the oil may become sticky and block the aperture diafragma

Should I panic, or is it not that bad after all?

Because it's not an automatic lens (aperture is preset), the diafragma is not making sudden movements, so the oil will not be splashing around.

And about the oil becoming sticky, that of course depends on the type of oil being used, but I'd guess that it may have a chance of surviving a couple of decennia?

Or do you think I should take preventive action and open the lens to try to remove excessive oil as much as possible?

Groeten,

Vic

 

[jaapv]

Better have it cleaned than opening it up yourself; It may be that the lens needs an optical bench to align the elements correctly.

 

[jlw]

Yup, oil on the blades is bad, for the reasons you mentioned AND:

-- The oil eventually will vaporize and fog the interior lens elements.

-- The oil will attract dirt.

-- [this is the really bad one] The extra surface tension of the oil causes the aperture blades to resist movement (even gradual movement.) This resistance can make them buckle. That can cause them to become bent, snap, pop out of their pivots, and/or arch up and scratch the surrounding lens elements.

All good reasons to have them cleaned ASAP.

Also, you have to reflect that the oil must have come from SOMEWHERE (all aperture blades are designed to operate "dry") and the most probable place is migration from the grease in the focusing mount. That means your focusing mount's lubrication has deteriorated also, and is no longer lubricating as well as it should (because the lubricant is now on the aperture blades instead of where it's supposed to be.) So, a lens with oily blades is probably due for a clean and relube of the focusing helix also.

 

[Bertram2]

Yup, oil on the blades is bad, for the reasons you mentioned AND:

-- The oil eventually will vaporize and fog the interior lens elements.

-- The oil will attract dirt.

-.

...and some oils are said to eat the coating after splashing on the glass surfaces !
There have been some Nikon AF lenses with this prob again and again
( 2/35mm) . At Nikon a design fault, the J8 maybe was CLAed by an amateur.

Regards,
Bertram

 

[vicmortelmans]

Thanks for the feedback so far! I will consider to do the cleaning myself. There's another thread I found about cleaning a Jupiter 9 (rangefinder version this time):

http://www.rangefinderforum.com/forums/showthread.php?t=2456&highlight=oil+solvent

but it doesn't say anything explicity on oil on the blades.

I've never used solvent before. If I end up opening the lens and have access the blades, is the solven just something I should spray on and wait until it has vaporated? Is it ok for the solvent to get in contact with lens elements?

I assume making physical contact to the blades using q-tips or whatever is to be avoided at all?

Groeten,


Vic