Sonnar diaphragm: matt coating?

[Grytpype]

Pre-war Sonnars I've cleaned have had what appears to be a matt coating on the diaphragm blades. This coating does not seem to survive a soaking in naptha.

Does anyone know of a solvent that will not affect the matt surface?

Steve.

 

[Dez]

I'm surprised that naptha is a problem. However, I use a rinsing solution intended for watch/clockmakers and an ultrasonic cleaner without any issues.

Cheers,
Dez

 

[Mr_Flibble]

I kind of assumed they were parkerized, if they weren't made of paper, celluloid or bakelite.

 

[Highway 61]

For having cleaned a fair amount of them myself I'd tend to think that the "matte coating" is an oxydization layer. Naphta dissolves the oily deposits having come from the mechanism damping grease, but leaves a slightly oily film behind, which makes them shine a bit.

Carefully cleaning the blades with a Q-tip soaked in acetone will make them become matte again.

On the postwar Opton lenses, the blades have been gun blueished... and aren't really matte, either.

 

[Grytpype]

I do think it is some kind of coating, but it would have to be a chemical coating like Parkerising as Mr Flibble suggests, so I am surprised it seems to disappear. I don't think the loss of the matt finish could be due to oil residue. I normally soak the blades overnight and rinse thoroughly and soak again if necessary. Anyway they look matt enough on the lens I'm working on now in spite of the pint or two of oil they are carrying!

I thought of trying water and detergent and the ultrasonic cleaner (I haven't got any of the rinse Dez suggests). I could do this if I strip the diaphragm, as I normally do, but I had decided it might be safer to clean it assembled, as the blades look rather fragile. Water between the blades would be near impossible to dry out.

Also wondered whether to try isopropanol and see if that is better than naptha. I'll try this tomorrow on a small area and see how it goes.

I haven't worried about this too much in the past - other lenses seem to manage OK without matt diaphragm blades - but I'm on my first 1.5 now and want to get it right!

 

[Highway 61]

There is nothing against soaking the whole thing in acetone. I've done this many times when naphta couldn't properly break out the old, hardened greasy layer which was on the blades.

 

[Grytpype]

Well the isopropanol doesn't seem to have any ill effect as far as I can tell, and seems pretty good at shifting grease as well, so I'll carry on, and give the diaphragm a soak.

Thanks for the suggestions.

Steve.

 

[Grytpype]

Update: I had another look at a couple of f2 Sonnars in which I had previously cleaned the diaphragm (disassembled) with naptha. They didn't look as un-matt as I remember, but greyish rather than black. One had a blade with no matt coating. This had not been obvious when everything was covered with oil, and I thought at the time that the coating had washed off, but in retrospect it is probably more likely it was a replacement uncoated blade.

I gave the diaphragm on the current f1.5 (still assembled to the barrel) three good soakings in isopropanol, and it was looking pretty good, but had a tendency to squeak slightly in operation, so in the end I decided to give it a wash in naptha. This didn't wash off the coating, but it did make it look rather less black than before, and seemed to highlight the wear-marks where the blades had rubbed together, so I guess naptha actually does no harm, but is just a more 'searching' solvent - and it did cure the squeak!

Interesting point: I've noticed that the brass diaphragm operating ring in this lens has two threaded holes for the operating screw, one blade apart. The 'spare' hole looks as though it may be a bit too close to the edge of the ring, so maybe Carl Zeiss decided to salvage a faulty part by drilling and tapping a new hole. You need to make sure you assemble to the correct hole or the diaphragm might be wrecked if you try to set it beyond its operating range.