[jaq1967]

Hello all,

I picked up an old Pentax-A 35-105mm f3.5 on eBay sold as spares/repair. Mechanically it is sound and there are signs of fungus. It will need a strip and clean. No big issue. However, I note the front lens has had some marks on it like there the SMC coating has rubbed/scratched off. Testing the lens there does not seem to be any major imaging issues/problems, and just needs a bit of TLC. Is there anything I can do about the marks on the front lens? Repair/rectify? See attached images.

Thanks in advance for suggestions.

It is quite a nice lens this, so would be good to try and salvage it. For £14.00 I can't moan too much.

Attached Images

       

[ProfessorBuzz]

Cleaning may reveal some of those spots are not damage to the coatings. There is nothing you can do to repair the coatings - they are deposited using specialize technology. Cost to fix exceeds the costs of a replacement.

[vonBaloney]

Just clean it. Test it by putting it at the widest setting and the smallest aperture (like f/22) and shoot into the sun (but at an angle), see if you pick up any weird spots or "unexpected" flare. If it doesn't do anything you find unacceptable, then don't worry about it. If it has a scratch deep enough to create weird effects, some say to fill in the scratch with a black sharpie to cut down on the effect. Never tried it, but might help. Most minor front element damage is not noticeable in images except with very wide-angle lenses where the front element itself is close to being in focus. But sometimes heavy dust or certain scratches can catch the light in ways you'll see.

[jaq1967]

Cleaning may reveal some of those spots are not damage to the coatings. There is nothing you can do to repair the coatings - they are deposited using specialize technology. Cost to fix exceeds the costs of a replacement.

I had a very basic look and did a quick clean of the front element as accessible. Those marks look like minor scratches to the coating. Initial imaging didn't show any major issues to photo's taken but i am sure on a sunny day or other they may effect imaging. Tbh... It doesn't seem like a massive deal. More concerning is the mild amount of fungus on glass but that isn't too difficult to clean up once stripped.

I know the coating is their to assist light transmission and stop flaring etc... If one was to remove the coating could one not use a protective filter? (Probably a dumb question and idea)? Could it not be polished off with automotive glass polish? Or... best left alone?

[ProfessorBuzz]

I know the coating is their to assist light transmission and stop flaring etc... If one was to remove the coating could one not use a protective filter? (Probably a dumb question and idea)?

No. The coatings are nanometers thick, designed for refracting various wavelengths of light, and are unique to each glass element surfaces (front and rear).

Could it not be polished off with automotive glass polish? Or... best left alone?

ABSOLUTELY NOT!!!!!!

All polishes contain very fine abrasives.
This would destroy the lens and likely change it's shape was well.
Do NOT do this.
I'd recommend you get proper lens cleaner e.g. Eclipse lens cleaner and lint-free Kim Wipes or PEC Pads.
This is super delicate stuff.

[jaq1967]

No. The coatings are nanometers thick, designed for refracting various wavelengths of light, and are unique to each glass element surfaces (front and rear).

ABSOLUTELY NOT!!!!!!

All polishes contain very fine abrasives.
This would destroy the lens and likely change it's shape was well.
Do NOT do this.
I'd recommend you get proper lens cleaner e.g. Eclipse lens cleaner and lint-free Kim Wipes or PEC Pads.
This is super delicate stuff.

I'll leave it then. Lol...

---------- Post added 06-29-2021 at 06:07 PM ----------

No. The coatings are nanometers thick, designed for refracting various wavelengths of light, and are unique to each glass element surfaces (front and rear).

ABSOLUTELY NOT!!!!!!

All polishes contain very fine abrasives.
This would destroy the lens and likely change it's shape was well.
Do NOT do this.
I'd recommend you get proper lens cleaner e.g. Eclipse lens cleaner and lint-free Kim Wipes or PEC Pads.
This is super delicate stuff.

How about a filler?

[Bob 256]

If these are indeed damaged coating spots, there is NOTHING you can do to fix them, and they probably will have very little if any effect on 90% of the shots you'd take with the lens. Do a careful cleaning of the front surface with a reputable lens cleaner (not one with silicone or the like in it - an optical lens cleaning solution only) and lens tissue, When done, breath on the lens and wipe with a clean lens tissue one more time. Anything that remains (spot-wise) is non-negotiably permanent unless it's inside the lens (and then it's still pretty much something you can't fix easily if at all). These might be an "oily" residue, in which case the lens cleaning solution, should do the job but there are some substances which bind to the lens coating in which case, forget it.


https://www.bhphotovideo.com/c/product/1097470-REG/zeiss_2127990_lens_care_kit_2oz.html

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Last edited by Bob 256; 06-29-2021 at 11:31 AM.

[dms]

A filter gives another air-glass surface for refections, e.g., from front of lens to filter and then back again, but unfocused. Doubtful there is any other difference, although one could speculate degradation over time in scratched areas, but even if there is the filter it will not change the local air conditions to something more favorable.

I suppose where (for example) salt water drops are possible it could, except I doubt there is a real difference between glass and the thin coating on the glass. I suppose with HF acid, maybe, but seriously the greater flare with the filter is the main thing that the filter adds.

[stevebrot]

How about a filler?

You're joking, right?

In case it is not clear from the comments above...There is nothing you can do to repair those fine scratches and abrasions. If you are concerned about flare, there is little need to but using a hood is never a bad idea. If you are concerned about optical degradation, don't be; the front element can take a fair amount of abuse without affecting image quality.* If you are concerned about appearance, get a different lens.


Steve


* A comment above mentioned 90% of shots. My estimate would be 99% for what is shown in your photos.

[ramseybuckeye]

The best you can do is use a hood, and enjoy your bargain lens.

[jaq1967]

You're joking, right?

In case it is not clear from the comments above...There is nothing you can do to repair those fine scratches and abrasions. If you are concerned about flare, there is little need to but using a hood is never a bad idea. If you are concerned about optical degradation, don't be; the front element can take a fair amount of abuse without affecting image quality.* If you are concerned about appearance, get a different lens.


Steve


* A comment above mentioned 90% of shots. My estimate would be 99% for what is shown in your photos.

Thanks... Yes, I was joking. 😊

[DWS1]

Nothing you can do about damaged coating.

[clickclick]

Check this out - rest easy and enjoy your new lens!

https://www.lensrentals.com/blog/2008/10/front-element-scratches/

[pentaxus]

Sometimes you can get an oily substance that binds to the coating and looks like that. Try 99% isopropyl on a swab and rub one of the dots and see if that helps. ROR lens cleaner can help also.

[vijaykishan]

Check this out - rest easy and enjoy your new lens!

https://www.lensrentals.com/blog/2008/10/front-element-scratches/

Excellent info in the link. Thanks for sharing, now I won't fret about that little spec of dust on the front element.