Removing AR coating

[tkamiya]

I have an enlarging lens that has some severe issue with AR coating in one of the internal elements. It's so far gone that the only way to save this lens is to completely remove the coating. (fungus has eaten away 25% of coating)

Is there a way to REMOVE anti-reflective coating without damaging the underlying glass element??

This is a Rodagon 80mm f/4. I can already get to the element.

 

[nick mulder]

hmmm,

If the fungus is just affecting the AR coating then you shouldn't have too much of an issue right ? (unless really stopped down and you project localised issues??)

I would have thought fungus poop would etch the glass itself also right ?

I know it's not helpful - but if you're saying that fungus is removing the coating only and not affecting the glass then maybe encouraging fungal growth is the method (!?)

 

[John Koehrer]

A method I've used is common toothpaste & lens tissue. It has to be paste not gel. apply the paste to the tissue & gently rub in a circular motion(Isn't that what Frank Zappa does in Dynamo hum?)

 

[ic-racer]

All of the enlarging lenses I have cleaned work fine with the residual damage to the coating. In side-by-side testing to new lenses, there is only a small decrease in contrast. Recall that negative overall contrast is only six to seven tenths of the original scene range.
http://www.largeformatphotography.info/forum/showthread.php?t=59159

 

[tkamiya]

This is interesting....

I took John's advise and used a small amount of tooth paste, water, and lens tissue and rubbed the coating off in gentle circular motion with periodic rinse. I repeated the process 3 times. Most of it came off QUITE easily. I still very little left but I stopped thinking it is now good enough. Going further may do more damage than good....

I reassembled the lens and voila! It's not half bad.... I'm now curious to put it on my enlarger and project some image to see how much damage I have done to the glass surface. Hopefully not enough to be a problem. Certainly, it went from not even worth trying to maybe it's good enough...

By the way, this was a lens I long ago written off as lost cause. The front element is scratched and inner element was badly damaged by fungus. First attempt at cleaning the fungus, good half of coating came right off. On top of it, departure blades are rusted. I would never have done what I did with something I valued....

Thanks everybody for helping me out.

 

[tkamiya]

Here's the results....

Comparing what I see in grain scope, the newly "repaired" lens (Rodagon) is....

MUCH better than Omegar in perfect condition
Slightly better than or equal to Comparon in good condition
Slightly worse than EL-Nikkor in great condition

If anything, it is MUCH sharper than Omegaron, just as sharp as anything else, but contrast is a bit lower than EL-Nikkor. I'm sure my attempt to restore it has a lot to do with it....