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Spots on rear element that won't clean off
Old 1 Week Ago   #1
Arbitrarium
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Spots on rear element that won't clean off

Hiya,

Yesterday I was working on cleaning and repairing a Balda Super Baldax. Aside from a bit of rust, it's now in great shape with a super bright viewfinder, accurate rangefinder and usable, if stiff, focus knob.

The only problem left is these spots on the rear facing of the rear element. Lens cleaner did nothing, even window cleaner did nothing. They're on the surface, as misting the glass with my breath shows. They don't appear to be bubbles as they are smooth to the lens surface. My guess is the coating's damaged but they really look like the glass has been sprayed with something and left little droplet marks. It's only on the rear element, the rest of the glass is clean.

Any ideas on a diagnosis or what to try? Cheers

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Old 1 Week Ago   #2
gdi
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Likely fungus has etched the coating ( hard to tell from the picture though).
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Old 1 Week Ago   #3
Sarcophilus Harrisii
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If a cotton tip very lightly moistened with acetone will not remove them then I think you're going to be stuck with them. "Very lightly moistened" because if you get any in contact with the painted lens retaining ring or any other painted components inside the back of the camera the acetone will do a superb job of stripping the paint off whatever it touches. So moist but not dripping, lightly swab the offending locations and see what transpires. You could always polish off the coating, but that seems rather a desperate measure at this juncture. The acetone won't damage the lens glass or a modern hard coating process from the last sixty-odd years or so. Less sophisticated soft coating technologies, (Eg older Leica lenses) definitely best to give it a miss.
Cheers,
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Old 1 Week Ago   #4
johannielscom
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Question is, what effect will it have on images, if any. Coating deterioration cannot be felt with your fingertip and you say glass is smooth, so it might just be the coating. I'd take the camera out and shoot a roll to see if anything is 'off'. If not, leave it be.


OTOH, if you want to be completely safe from fungus: If there's fungus (or any other organic matter) present, a 50/50 mix of hydrogen peroxide and ammonia will remove it.

Remove the lens element to carefully soak it in a shallow dish. Wear gloves and leave the element in the solution for 5-10 minutes. You might see bubbles form. Then rinse under warm water with a drop of dish washing soap and dry carefully with a clean cotton cloth while still warm.

Unlikely that those stains will disappear though, they really look like coating stains.


Happy shooting with the camera in any case!
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Old 1 Week Ago   #5
Arbitrarium
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Quote:
Originally Posted by johannielscom View Post
Unlikely that those stains will disappear though, they really look like coating stains.


Happy shooting with the camera in any case!
Cheers dude. Yeah my best guess is coating damage. I'm not too worried about it affecting pictures as it's only properly visible at the right angle, and a rear element shouldn't be picking up glare so...

Just a bit of a shame as (as an amateur camera restorer) I was very pleased with myself for fixing everything else on the camera!
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Old 1 Week Ago   #6
Mark Wood
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I've got a Baldix folder with a Baltar lens whose front element is peppered with similar spots on its front surface. It doesn't seem to affect image quality in any obvious way (it still gives very sharp images for a triplet lens), although without an unmarked lens for comparison, that's probably a pointless statement!

I'd certainly just use it now everything else is working properly, the Super Baldax is a really nice camera.
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Old 1 Week Ago   #7
sevo
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Coating damage. On coatings from that era it might be a fabrication flaw, on more modern cameras it usually is secondary to fungus, or to exposure to rain or to sea water spray.

It is irrelevant - that will amount to maybe 10% without coating, on a Tessar type, i.e. a lens famous for delivering high contrast even when entirely uncoated.
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Old 1 Week Ago   #8
Arbitrarium
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Quote:
Originally Posted by sevo View Post
Coating damage. On coatings from that era it might be a fabrication flaw, on more modern cameras it usually is secondary to fungus, or to exposure to rain or to sea water spray.

It is irrelevant - that will amount to maybe 10% without coating, on a Tessar type, i.e. a lens famous for delivering high contrast even when entirely uncoated.
...10% what? You confused me there.

p.s. This Super Baldax has the Ennit lens. I believe it's a 4 element and the top of the range on the Baldax. Was a lucky find
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Old 1 Week Ago   #9
sevo
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Quote:
Originally Posted by Arbitrarium View Post
...10% what? You confused me there.

p.s. This Super Baldax has the Ennit lens. I believe it's a 4 element and the top of the range on the Baldax. Was a lucky find
The spots where the coating has become damaged seem to make up something like 10% of the total area. And the Ennit is a Tessar copy.
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