[Scott_the_Artist]

None of my lenses have oil on their aperture blades, but why is this a big deal? What problems does it cause?

[smigol]

When old lenses have oil on the blades, they can be slow to react when the shutter is triggered. This mostly effects when you're shooting with high f numbers, when the blades would have to travel the furthest to stop down the exposure.

[X Man]

None of my lenses have oil on their aperture blades, but why is this a big deal? What problems does it cause?

Well, with a K mount lens, whether it's an "A" or an "M", oil on the aperture blades will make them sluggish. So, imagine needing and exposure of 1/500th and the blades taking ten times longer than that to open or close. Not so good, huh?

Now, with M42 lenses it really doesn't matter if they are used on a K-Mount body film/or digital as we're stopping down with the aperture ring and not relying on the spring action on the blades for correct exposure.

Hopefully that was semi-coherent.

Regards,
Mike

[SOldBear]

None of my lenses have oil on their aperture blades, but why is this a big deal? What problems does it cause?

Note that when attached to a camera body the aperture stays open.

When you hit the shutter release button, the aperture closes down to whaterver the aperture setting is, then the shutter opens, then closes, then the aperture opens up again. All happens in a split of a second. (Unless the lens is a "preset" lens that needs to be manually closed down before shutter release).

So the aperture blades have to be "snappy." Otherwise the aperture won't close completely to the aperture setting. It "kind-of" closes and then opens. The result will be an over-exposed photo.

Oil (mainly from the grease deteriorating) can get in between the aperture blades, making them "stick" together. Over-exposed photos from a particular lens is a sign of oil contamination.

The only way to fix this problem is to completely disassemble the lens, then wash the aperture blade with solvent (I use naptha). I currently have a lens waiting to be assembled back, and another one waiting for the naptha bath.

[KungPOW]

I love the Jupiter 9. The lens smells like gun oil. Russian gun oil.

I think the aperture blades are held in place by the thick layer of oil on them.

The lens is exactly what you do not want in you K mount lenses.

[Scott_the_Artist]

So, from what I gather, since I'm shooting with a k20d and using full manual only for older lenses, it doesn't matter at all if oil is on the aperture blades or not.

Anybody have any old Takumar lenses with nice oily/greasy aperture blades that they'd like to sell me at a discount?? (joking, sort of)

[pbo]

So, from what I gather, since I'm shooting with a k20d and using full manual only for older lenses, it doesn't matter at all if oil is on the aperture blades or not.

It doesn't matter if you're shooting m42's or preset K-mount lenses (i.e. those that actually close down as you turn aperture ring).
If you're shooting a normal K lens, i.e. the one that stays open until you trip the shutter, then oil will be problematic and most probably result in overexposed images (since aperture doesn't close to the right aperture when shutter trips).

[Kerrowdown]

Makes the blades sticky, slows 'em down.

[GerryL]

Another thing that hasn't been mentioned yet is that of course you have to wonder where the oil came from???
If the aperture has oil on it, not only does it slow down, but it is telling you that some part of the lens has broken down and the oil that is supposed to stay at that specific part is now on the aperture and not the intended mechanism.

[Scott_the_Artist]

So it's not something that is just inevitable as a characteristic of aging lubricant? Are you saying that it's always indicative of a repair that will soon be necessary instead?

[Ratmagiclady]

So it's not something that is just inevitable as a characteristic of aging lubricant? Are you saying that it's always indicative of a repair that will soon be necessary instead?

It depends, really: some brands and designs seem more prone to this than others: actually, the most frequent cause in major-brand lenses seems to be a poor re-lubrication job with the wrong stuff.

[GerryL]

So it's not something that is just inevitable as a characteristic of aging lubricant? Are you saying that it's always indicative of a repair that will soon be necessary instead?

This usually happens when the lens is left inside the car and the car becomes an oven because of the heat.
The lubricant breaks down and runs.
The lubricant shouldn't run as it is the viscous type.
That is also the reason why the apertures are no longer snappy as it is oil that isn't actually making things slippery but a bit sticky.
Some of these lubricant are applied to zooms so as to minimize zoom creep.
The repair of such lenses with oil on the blades requires removal of the oil with a solvent.
The re-lubrication of the part where the oil came from usually isn't done and left as-is.

[paugie]

I have a lens which has sluggish aperture blades. So I use it only wide open.
Now, is there a way to take pictures with a K20D where one can stop down the lens manually before firing the shutter?

[Just1MoreDave]

I have a lens which has sluggish aperture blades. So I use it only wide open.
Now, is there a way to take pictures with a K20D where one can stop down the lens manually before firing the shutter?

If you partially dismount the lens, the aperture control arm in the camera won't reach the lever in the lens. The aperture ring can then be set at whatever aperture you want. The disadvantages are a loose lens which can fall off, and it's hard to focus well at small apertures.

[Steinback]

@paugie: If you are mechanically handy it is possible to remove the aperture control arm completely. One of the other Toronto Pentaxians did this with his M 20mm so that he could use it in aperture priority mode.