Oil on aperture blades?

[tinglers]

How can you tell if the oil is actually oil? I see that there are some marks near the blades near where the apertures overlap when they are shutting down, however I can't tell if its oil or just marks. So how can I actually know for sure?

 

[splitimageview]

It's difficult to tell sometimes, for sure; try using a flashlight (preferably LED type) and see if you can detect glistening as opposed to marks due to usage...

 

[mirrored]

Viscosity of the vaseline can change, and run to wrong places.

On RF, what matter? There is no movement when shoot. In SLR it make blades slow.

Sometimes wearing or old dry marks of oil cannot easily differ from moist oil.

 

[ChrisN]

On Leica lenses it can often be a polish on the teflon coating on the blades that gives the appearance of oil (or so I have read elsewhere).