How to deal with the soft coating in Minolta MC lens?

[kl122002]

I have a Minolta MC 58/1.4 on table and I know the coatings behind the front lens is really soft, which the lens cleaner could almost dissolve it.

Any tips in how to clean the fungus there ? I plan to use detergent with clean water for a try.

 

[Andreas Thaler]

I have a Minolta MC 58/1.4 on table and I know the coatings behind the front lens is really soft, which the lens cleaner could almost dissolve it.

Any tips in how to clean the fungus there ? I plan to use detergent with clean water for a try.

I kill the fungus with hydrogen peroxide. It's best to try the products out on a small area on the lens first.

 

[Richard Jepsen]

I still have my 1968 SRT camera kit with MC lenses. Minolta hard coated the optics. That said you can’t mishandle optics.

 

[Sirius Glass]

I still have my 1968 SRT camera kit with MC lenses. Minolta hard coated the optics. That said you can’t mishandle optics.

I bought a used Minolta SR-7 in 1966 and owned MC and MD lenses. I agree that you cannot mishandle the Minolta optics.

 

[xkaes]

I know the coatings behind the front lens is really soft

What does "I know" and "really soft" actually mean? As two other responders -- I'll add myself to the list -- have said, Minolta coatings are "hard".

 

[Andreas Thaler]

Unfortunately, not all Minolta lenses are hard, in the sense of physically resistant.

While cleaning I scratched one of the inner front lenses of my MD 135/3.5, the back of which was soft.

I was also able to scratch this lens with the pointed probe, which is otherwise not possible.

 

[Richard Jepsen]

I would think a pointed probe would mar a coating. When one speaks of soft coatings it brings to mind the 1950-60 Leica coatings that used an evaporative method to coat.

When one mention a hard coating we are not talking about a scratch resistant iPhone screen.

 

[xkaes]

Maybe we should get specific:

 

[kl122002]

What does "I know" and "really soft" actually mean? As two other responders -- I'll add myself to the list -- have said, Minolta coatings are "hard".

My experience is the outer coating of both ends of the lens are "hard", can be cleaned with common cleaning fluid without damaging, but for the inside, just behind the first element is relatively "soft". I have seen some turned into haze-like after the user attempted to clean.

 

[xkaes]

Does that make it GYPSUM or TALC?

 

[kl122002]

Does that make it GYPSUM or TALC?

In other words , you sure it's not about chemicals reaction on the inner coatings?

 

[MattKing]

In other words , you sure it's not about chemicals reaction on the inner coatings?

I'll bet he is referencing two of the entries on the Hardness scale.

 

[kl122002]

I'll bet he is referencing two of the entries on the Hardness scale.

Perhaps my English isn't good enough. The lens coatings that I use " hard/soft" is because how it is called around in my place. Older coatings (like single coating made in 1950s, or some that could be easily scratched or mess up ) is considered "soft" . On the other side " Hard" is more like modern coatings that could even handle alcohol cleaning without issue.

And this is how and what exactly happened. I got a 58/1.4 and I checked, obviously it has been opened before me (from checking the retaining ring marks) , cleaned once leaving a thin haze. But now I am asked to help remove the fungus and so I not sure to try, or take the risk.

 

[MattKing]

This is what the reference is to:

 

[kl122002]

This is what the reference is to:
View attachment 364219

A follow up here.

I am now very sure about this scale . But here I tried tested it with Fuji lens cleaning fluid at the corner with lightest touch, after dry it left a slightly post-cleaning mark there. It is not from the glass but from the coating when checked with scattered light.

I gave up and just returned to the original owner .

 

[reddesert]

Colloquially people refer to "hard" and "soft" coatings where a hard coating is resistant to chemical attack from typical cleaning solvents and soft physical abrasion (like from a cleaning cloth), while a "soft" coating is not and can be damaged by aggressive cleaning.

Coatings were originally motivated by people who noticed that a tarnish that formed on lenses improved the transmission. That kind of tarnish can obviously be wiped off by cleaning. Some early lens coatings such as the Leica coatings Richard Jepsen referred to are also said to be "soft" and vulnerable to attack by solvents. Standard coatings such as MgF2 are quite hard and you don't have to worry about damaging them with alcohol or lens cleaner. These would have been common practice by the time of a Minolta MC lens, and I don't know why they might have used a "soft" coating on inside surfaces unless it was an early multicoating that was more vulnerable.

Sometimes haze that is hard to get off seems to come from the cleaning fluid pushing oil on the surface around. I have a couple of filters like that - ordinary lens cleaner just doesn't seem to clean them.

"Hard" and "soft" in coatings doesn't really have anything to do with the Rockwell or Mohs hardness scales - you can scratch any glass lens or thin film with a sharp object if you try - and I think it was a distraction to bring that up.

 

[xkaes]

Thanks for that excellent clarification. We often talk using the same words, but with different meanings.

Along the same lines, Minolta always created confusion with the "MC" designation on their lenses. Some people think it means "Multi-coated", but Minolta used it to mean "Meter-coupled". Minolta never used the term "Multi-coated" for their lenses -- although they marked most as "MC" (and later, "MD"). Minolta referred to their multi-coatings as "Minolta achromatic coating" -- and many of their lenses and filters are marked "AC", which can also be misinterpreted, as you might imagine!

 

[Chuck1]

Lens cleaner doesn't really do much, any recommendations for something less aggressive than alcohol?

 

[kl122002]

Colloquially people refer to "hard" and "soft" coatings where a hard coating is resistant to chemical attack from typical cleaning solvents and soft physical abrasion (like from a cleaning cloth), while a "soft" coating is not and can be damaged by aggressive cleaning.

Coatings were originally motivated by people who noticed that a tarnish that formed on lenses improved the transmission. That kind of tarnish can obviously be wiped off by cleaning. Some early lens coatings such as the Leica coatings Richard Jepsen referred to are also said to be "soft" and vulnerable to attack by solvents. Standard coatings such as MgF2 are quite hard and you don't have to worry about damaging them with alcohol or lens cleaner. These would have been common practice by the time of a Minolta MC lens, and I don't know why they might have used a "soft" coating on inside surfaces unless it was an early multicoating that was more vulnerable.

Sometimes haze that is hard to get off seems to come from the cleaning fluid pushing oil on the surface around. I have a couple of filters like that - ordinary lens cleaner just doesn't seem to clean them.

"Hard" and "soft" in coatings doesn't really have anything to do with the Rockwell or Mohs hardness scales - you can scratch any glass lens or thin film with a sharp object if you try - and I think it was a distraction to bring that up.

Thanks for brining this up! I thought the terms I used in here is exactly same as the people here

 

[kl122002]

Lens cleaner doesn't really do much, any recommendations for something less aggressive than alcohol?

Detergent + water. Sometimes it works.