Oily aperture blades

[Terao]

Why are they considered to be an issue? If the blades move smoothly and don't stick surely it makes no difference? Or is it because now the oil is out on the blades that it will eventually dry out and get sticky?

 

[Ororaro]

Exactly!
Besides, it shows the lens has a fault.

 

[Kim Coxon]

It comes from users of SLR lenses with autostop-down. If there is oil on the blades, they will be sluggish which will affect the exposure. Whilst this doesn't affect either preset lenses or those for RF use, the oil could could reflections/flare.

Kim

 

[vicmortelmans]

it is also said that the oil can vaporize and condens again on lens elements, influencing their optical performance.

 

[David Murphy]

It's a negligible problem if evaporation and diffusion of the oil is not causing haze. It's much better that an old lens have oil on the blades than have rusted blades (oil prevents rust). I do not regard oil on the blades as sufficient justification for a CLA if the lens is good otherwise.

 

[Terao]

Thanks all. Just looked at my Jupiter 9 and couldn't believe how much oil there was on the blades. I think its central heating to blame, these lenses were designed for winter in the Urals 😀

 

[David Murphy]

What I was told by a camera tech was something to the effect that all iris blades have oil, but it is special oil designed not to diffuse out. Over time this still happens (i.e. over a long time).

 

[jlw]

No, oil on the blades is bad -- not only as a symptom (that lubricant has migrated away from parts that should have it) but also in itself.

Unless you've ever taken a diaphragm mechanism apart, it probably wouldn't occur to you how delicate the blades and pivots are. (If you have taken one apart, you know exactly what I'm talking about!)

The bad thing about oil on the blades is that it attracts dirt, which causes it to get gummy, which in turn makes it more difficult for the blades to slide across each other. Eventually they'll be stuck together enough that when you try to turn the aperture ring, one of these bad things will happen:

-- A blade will come off its pivot, or shear its pivot pin completely off. (I once had an otherwise good Konica I that was damaged in exactly this way.)

-- The blade will arch upward enough to crease it, ruining the diaphragm mechanism. (I had a 135mm Bronica Nikkor lens that had fallen victim to this.)

-- The blade will arch upward enough to scratch the interior surfaces of the lens. This is the mega-bad thing, because it means optical as well as mechanical damage. (Lucky for me, I've never had this happen, but it can happen.)

Incidentally, while it's not impossible, I've personally never seen a diaphgram mechanism that was designed to be oiled. The pivot pins generally are brass, which has a natural lubricity; they operate in holes and slots with fairly generous clearances, so there isn't a lot of friction that would need to be relieved by lubrication; and they move short distances without a lot of force, so they don't have a high potential for wear. Liquid lubrication simply isn't necessary under these conditions. Maybe a tiny drop of non-migrating lubricant on the pivot pins during original assembly, but that's about it.

If you don't believe that mechanical parts could be designed to operate without lubricants, remember that old mechanical clock mechanisms also were designed to run "dry." Oiling an old clock will ruin it, and for basically the same reason it's bad for diaphragm blades: the oil attracts dirt, which accelerates wear.

 

[BrianShaw]

If you don't believe that mechanical parts could be designed to operate without lubricants, remember that old mechanical clock mechanisms also were designed to run "dry." Oiling an old clock will ruin it, and for basically the same reason it's bad for diaphragm blades: the oil attracts dirt, which accelerates wear.

Not exactly true. Old mechanical clock movements REQUIRE proper oil and grease to run. The emphasis is on proper oil: pure and non-migrating, and proper lubrication methods: tiny amount at pivots (the "pins" that hold the gears into the clock plates) or on sliding surfaces. Without lubrication, clocks don't run. Even clocks using jeweled mechanisms like watches need oil at the jewels.

There are companies that have worked for generations developing fine watch/clock oils/greases. These oils and greases are subject of considerable scientific improvement even today. Once it was common to use biological-based oil - sperm (whale) oil, then petroleum-based oil (Nyoil, for example) and now synthetic oils tend to dominate this specialty lubricant market. Greases, too, have gone through similar evolution.

I believe what you intend to emphasize is that there are parts that are meant to be lubricated, and parts that are not meant to be lubricated. Those that are lubricated are not intended to run forever without periodic PROPER cleaning and PROPER re-lubrication. And improper lubrication will lead to premature failure of the device - whether it is a clock, watch, or camera.

The problem in clock lubrication is MIGRATION of the oil... just like in camera shutters. If too much oil is placed, even in the right place on a clock, it will migrate away and not provide lubrication at the pivot point where it belongs -- the oil will simply gunk up the clock plate and make it dirty. In a camera, as you say correctly, too much oil in the wrong place will migrate onto parts it doesn't belong on and gunk them up -- leading to a different type of failure/damage.

It is true that oil attracts dirt and dirt causes wear. In old clock repair it is common practice to re-pivot -- replace the pivot by reaming out the old one and re-fitting a proper sized bushing in replacement. The pivot wears out from one of two reasons: lack of lubrication, or the abrasive grime that builds up in the oil. This is one of htose 'darned if you do; darned if you don't' situations - the oil keeps it running smoothly but leads to eventual wear; but the wear is going to happen with or without oil.

There are some leaf shutters in cameras that are alleged to be designed to run without oil; there are others that won't run at all unless they are properly oiled. Those skilled in leaf shutter repair know the difference. Those not skilled will goop up the mechanism with lots of 3-in-1 or WD-40 and cause the shutter to totally stop sooner than later.

In conclusion (since you inspired me to get on my soap box... one which I am most adamant about because of the large amount of incorrect information floating around the internet by people who are both trying to properly learn the trade or, alternatively, are trying to effect a quick-fix without too much concern for longevity of repair), let me re-iterate the following:

Mechanical clockwork devices, like clocks, watches, and shutters are not intended to run forever without periodic PROPER cleaning and PROPER re-lubrication.

 

[jlw]

Point taken, but I meant the gears specifically, not pivots, escapements, etc.

To quote J. E. Gordon, Professor of Materials Technology at the University of Reading, U.K. (he's more or less the father of composite fiber technology, among other things) in The New Science of Strong Materials [Princeton, N.J.; Princeton University Press, 1968, 1976]:

"Hammering a metal to harden it is not uncommon: this was the way of hardening the edges of copper and bronze weapons and the old clockmakers always hammered their brass gear wheels. (If one refrains from oiling the gear teeth of a grandfather clock, the teeth will not only not collect the dust and so not grind each other away, but also become harder and more polished as time goes on and so last virtually for ever.)[Emphasis added.]​

In any case, diaphragm blades aren't clockwork mechanisms; they slide over each other at slow speeds and with low force.

Clockmaker Brian obviously knows what he's doing, but while you other guys can oil your diaphragm blades if you want, don't try to go oiling mine! And I'd still avoid buying lenses with goop on the blades. Even if you assume that diaphragm pivot pins require lubrication, the fact that the stuff has gotten onto the blades suggests strongly that the right type of lubricant was not used.

 

[BrianShaw]

Point taken, but I meant the gears specifically, not pivots, escapements, etc.

Okay. Your statement about clocks appeared to be a blanket statement about mehcanical clocks in general and got me going. You (and Gordon) are quite right about not greasing gears. That's one of hte quickest ways to "gum up the works." Gordon is also really right about work hardening brass and the benefits in some situations. In other applications this technique - e.g. shot peening - is effectively used with cast iron components. As a job while I was in college I shot peened hundreds of connecting rods for auto engines being prepared for racing.

You're right about diaphrams - they aren't supposed to be oiled, even the pivots. That's just asking for problems. I cringed when I read about a camera tech actually telling someone that they are supposed to be oiled. Clean and dry is a better rust preventative than oiled! I believe that shutter blades often have their pivots lubed, but that is a totally different type of stress than the aperture blades. (Same concern, if not more serious, about oil migration if not done properly.)

I'm with you about avoiding any lens/shutter that has evidence of oil problems. Sometimes it turns out to be a real bargain that 1 or 2 hours work will cure; othertimes it turns into just another part for the junk drawer (which is already overflowing).

p.s. I prefer to be called "Herr Clockmaker Brian" -- I specialize in German clocks 😉

 

[bsdunek]

As a 'used-to-be' camera technicion (got my degree from the old National Camera school in Colorado), the only thing that might be used was a dusting of graphite. This was more often used on shutter blades, but occassionally on diaphram blades. Today, one might use a dusting of Teflon (they didn't have that then). In any case, any liquid lubricant was not to be used. Even with manual lenses, when it's cold the oil can become stiff enough to bind the blades, resulting in the damage jlw has mentioned.

Sometimes it's a deposit from evaporating focusing thread grease, and that will get really thick!

Best to have a good cleaning of that lens by a qualified repair shop before you come to grief. IMHO 😎