[cyberjunkie]

I bought a damaged Sigma EX 30mm f/1.4, with the intention to fix it.
More details in the original post:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/272999-help...based-usa.html
I had the intention to buy a replacement front glass, but i found that the damage is different from what i expected (and dismantling the objective is not as easy as i thought!).
What i know is that the front glass was damaged by the explosion of a firecracker.
From the picture the damage looked like tiny dots (indents), caused by material hitting the front glass.
That's how it looks at close inspection, but if i try to scratch the surface of the lens with my nails, i can easily feel that there are no cavities. There are small bits of transparent, glass-like material glued to the glass!
Probably when the firecracker exploded, some particles melted from the high heath, and were projected against the front glass of the lens. Of course the glass was way cooler, and the particles got stuck to the glass.

When i find fungi, or stubborn dirt, i use isopropilic alcohol. I didn't try cause i don't have any at the moment, but i will in the next days.
Somehow i feel it won't be enough. So i am asking about your "secret recipe" to clean stubborn dirt.
It must be strong enough to dissolve the stuff glued to the glass, but not enough to attack the coating.
A fluid that does not affect plastic materials would be the better solution, but i'm prepared to use a small sponge (or a cotton bud) to apply the fluid only to the spot.
Of course it must not affect the multi coating in any way.

I tried to search the forum for this kind of information, but to no avail. So i thought it was well worth starting a new thread about the subject.

Thanks in advance

Paolo

[racingsnake]

WD40 is known to work wonders

[wildlifephotog]

I've seen that exact damage before. Those marks are damage to the lens coating. It won't clean off or polish out.

[cyberjunkie]

I've seen that exact damage before. Those marks are damage to the lens coating. It won't clean off or polish out.

I would be happy to get to that point. Stains/marks to the coating... it would mean to have a 99.99% perfectly working lens!
I have seen a large format lens, with visible markings to the coating, used for top tier work (read 8x10" for major advertising campaigns... not the humble catalog work i used to do myself, with spotless glasses! ).
BTW, how do you know? I didn't post any picture, and i wrote that from the auction photos, and even at first sight (from very close), the damage looks different from what actually it is.

WD40?
Never heard about it
I've read any kind of advices on early 1900 (or late 1800) manuals, when the photographer had to be a DIY fellow, and the environment could be quite... rough.
Even re-polishing the glass was not an uncommon practice, but there were no super-thin coating layers...
Being a large format lens collector, i know that early coatings were quite soft, and very easy to damage. Though i do know that modern coatings (as in a Sigma EX lens) are very resistant, much more than the optical glass, but i have no informations about the solvents that can be used, and those to be avoided.

cheers

Paolo

[wildlifephotog]

How do I know?

Because a friend tried a stunt with a firecracker and trashed the front element of his lens.
I ended up replacing the element for him.

[Achromatter]

If you're sure it's particles stuck to the lens, I'd try gently and evenly applying heat to the front element with a hair-dryer, or a heat gun set to "low", and see if you could pry them off with your finger nail. If the particles were truly "molten hot" when they landed on the front element, it's possible the coatings melted and fused to the particles.

What's worse, using the lens as is, or using it with dots, or more, of the coatings missing from removing the "particles"?

[altopiet]

BTW, how do you know? I didn't post any picture, and i wrote that from the auction photos, and even at first sight (from very close), the damage looks different from what actually it is.

It might help if you can post a close-up shot of the damage to the lens...., but from what you describe, and having done some grinding work next to my car, (yip, lesson learned) the hot grinding particles actually melting the glass and fusing itself into the glass, I can't see how it would be possible to remove it, and the coatings are most probably damaged in any case...