New Lentar 28mm lens is nevertheless frozen

[guardian]

I hope somebody has a suggestion on this. I'm out of ideas, at least for the moment:

Brought in a couple of NOS (new old stock) Lentars:

Click here to see on Ebay

Click here to see on Ebay

Both were manufactured a long time ago. On the first lens, the 200, the focus is quite stiff but it is OK and usable. I could re-lube the lens but, for now at least, I most likely will not do so.

It's the second lens, the 28 also NOS, that's giving me serious fits. The focus is completely locked. It is frozen!! Aside from that the lens itself is clearly brand new and unmarked. The glass is perfect in every respect, for example. There are zero scratches. There is no indication whatsoever of anyone ever having worked on the lens. It's new! But it's frozen.

So far:

So far I've tried the tricks I have in my kit. I was fortunate to be able easily to remove both the front and rear lens groups while doing no damage whatsoever to the lens. It's perfect glass and I set it carefully aside.

What's left is the all metal barrel (no plastic in these older lenses) but with helical absolutely frozen tight . . no motion whatsoever.

First I tried acetone . . lots of it. Nothing.

Then I went to the garage and grabbed my Bernz-O-Matic (propane) torch. I heated the barrel to a pretty high temperature (no damage done) in hope of something breaking free. Using cloth to protect my hands from the hot metal, I tried to unscrew the helical. Nothing. It remained frozen solid!

My next thought is to immerse the thing in gasoline (petrol), but I've not tried that yet as the lens barrel is likely forever to smell of gasoline even after thorough cleaning.

I really don't know what could have that helical so frozen, especially on a brand new (old) lens. I do note that it appears to be brass inside (what I think is) aluminum (aluminium). Perhaps galvanic action over the years has done the poor lens in.

Does anyone have any thoughts as to what I should try next?

[Lloydy]

If it's desperate measures, then I would heat the metal parts wit a hot air paint stripper until it's as hot as you can get it and throw it in iced water. The two metals will have a different coefficient of thermal expansion and should expand / contract at different rates.

If acetone hasn't seeped through the helical, then I doubt much else will. But how about a weak acid such as vinegar?

I had an old Range Rover for a few years and the galvanic corrosion was a nightmare. I think there are far more ways of preventing it than fixing it.

[guardian]

[Lloydy]

I don't think you will need enough heat to damage the paint, if you use a hot air gun be careful. If you're prepared to get it wet use a pan of boiling water and a pan of iced water and cycle it between the two. The important thing is to get the heat / cold through all the metal and not just the surface.

[guardian]

Here is an update on the above-described dilemma. Progress so far:

Epic fail


I dismantled the lens, removing all glass including front and rear groups.

Inserted front of stripped lens into dish of ice water, thereby protecting paint.

Thoroughly heated rear (protruding) portion of lens with propane torch.

Inverted the (stripped) lens.

Gosh, that certainly did not work. I may try again, but this helical is really locked.

It's such a pity. The lens is literally brand new.

The good news (there's not much):

I don't seem to have destroyed the lens yet. Aside from a bit of harmless discoloration where I played the torch, all is OK.

[Lloydy]

time to get brutal......try 'gently' distorting the lens into an oval shape, just enough so it springs back to round, and keep doing all around the lens.
The other option is to put some sustained firm, but not damaging, end to end pressure on the helicoid and then give it the hot and cold treatment.

[guardian]