Canon Canonet QL17 G-III rear lens element - white deposits

[Kino]

I was handed a nice Canon Canonet today by a friend who knows I like to dabble in repairs.

The camera is in good condition except for the non-functioning meter (most of them die anyway) and the rear element having very strange white deposits on the rear element. It certainly doesn't look like fungus; more like calcium deposits. The patches actually are on the surface of the rear element facing the film plane and they are rough to the touch.

I have started with alcohol, went to half and half peroxide and ammonia, then to acetone and am now soaking it in vinegar. They have dulled somewhat, but are still there.

Kind of at a loss as how to proceed...

Suggestions?

(sorry for the dirty fingers!)

 

[Kino]

I am beginning to think this is etching from a prior fungus attack...

 

[shutterfinger]

Looks like fungus to me.

 

[Kino]

The lens is certainly etched. Too bad.

Into the spare parts bin it goes. Pretty sure I have another model around here with a clear rear element.

A future project...

 

[John Koehrer]

If it's going to the parts bin, why not try a bit of toothpaste as a polish? a small piece of the damage will be enough to test.

 

[AgX]

At this stage of testing I would start polishing.

 

[Kino]

I tried a bit of Flitz metal polish; no effect.

 

[AgX]

You need harder abrasive, some that takes off the glass too, as it likely has been etched.

But as Nodda Dumma hinted at in your other thread, it takes a bit of tooling to do it the best way.

 

[Kino]

I'll just stash it away. Maybe someone on here might need it some day or I'll try to find a donor for a rear element.