help: cleaning Vaskar rear element on Bessa I

Well, that was fun… nothing to lose, so to speak...

overnight soaking in Windex: no result
Methylated spirits applied with cotton bud (Q-tips): no effect
soaking/rubbing with Acetone: no effect
Ponds hand cream/cold cream, prolonged very firm polishing action using cotton buds: no effect
Colgate Advanced Whitening toothpaste with Micro-Cleaning Crystals, using a vigorous circular polishing action with a cotton bud: now we're talking.. this didn't eliminate the haze, but it did noticeably diminish. Un-hazed areas of glass appeared unaffected.

Conclusion: My hands have never been softer from the Ponds, and the lens smiles a bit more brightly from the toothpaste (probably those micro-cleaning crystals). I was wondering if the Advanced Whitening might give me another stop of brightness just like it does for my teeth, but I'm not getting my hopes up. I think it will remain an f4.5 lens :(. But maybe it will now have some glow, like a Summitar :)

So I re-assembled the Bessa, thoroughly scratching the mounting/locking ring in the process by using two jewellers screwdrivers as a two-handed lens spanner. Not wanting to risk wasting a fresh roll of expensive film, I loaded a roll of ancient, poorly stored Tri-X gifted to me by another photographer along with some darkroom stuff. The film packaging looked faded and ancient.

I exposed normally and, in keeping with the antiquity theme, developed it in XTOL that's about a year old. Why can you only buy that stuff in 5L amounts?

The developed negs were more transparent than a porn star's negligee. Or at least what I imagine a porn star's negligee to look like. With my glasses on.

Scanned in the V700, and here is the result. I think it warrants a roll of real, fresh, HP5+ as the focus seemed OK and I couldn't tell the difference between haze-induced softness and my crap processing:

13076572994_438d2e4261_o.jpg
 
here's another from the first roll of long-expired, grievously underexposed Tri-X. This would probably rate as good processing at my local pro lab…
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Fungus ( and it looks like you have some ) responds to a 50/50 mix ammonia and water. Just soak it, and the fungus may wilt away.

Another options I use is a lens cloth and whitening tooth paste. The whitening in the tooth paste is the mildest abrasive you can often pull off on an uncoated lens.
 
... I fancy the fungus has etched the surface of the glass, I don't see how any organism could stand up to that lot
 
My guess is that the problem is likely due to the type of glass used in the rear element. A lot of Canon LTM lenses have similar haze on specific elements in their optical formula because whatever Canon used to get the right refractive index in the glass makes them very susceptible to it. One very well known lens repairer in Tokyo (the go to man for polishing, recoating, or recementing lens elements) I asked about Canon LTM lenses said he refuses to accept them for repair because they just get hazy again after he cleans them.
 
I have two 1930s (non-rangefinder) Bessas, even older, that have lenses that are clean and clear. Maybe they changed the glass later, but I can't say I've ever heard of older or newer Voigtlander lenses suffering this as an endemic problem. Perhaps others can elaborate.
Cheers
Brett
 
Since you had some success with an abrasive, it is pretty clear that you've got an etched lens element. If you want to try to go further with it, I have seen more improvement with silver polish than I have with toothpaste. FWIW, I use Flitz, which is billed as a general metal polish; you want something safe for softer metals but with an abrasive component, not purely chemical.
 
Finally put a roll of fresh HP5+ through the camera.. the results seem quite acceptable. Looks like I have a user.

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by lynnb on Flickr
 
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