lens scratch repair... possible?

[CLee]

I recently picked up a Olympus 35-70 3.6 lens on ebay (I ususally buy from KEH, but they have not had any for a while). When it arrived the front glass was way more scratched than the poster said it was. I got a refund, but he seller didn't want the lens returned.

So it got me to thinking, is there a relatively cheap way to fix scratches in the front glass. There are MANY very light scratches. Not just in the coating but slightly in the glass. Like the glass was poorly cleaned or spent time rubbing up against something.

I'm figuring the answer is no, but thought I'd ask before putting it up on a shelf...

 

[fschifano]

To answer your question, no, I can't think of anything you can do to repair scratches in glass other than to regrind it. Obviously, that's not practical on a couple of levels. Aside from the expense of the equipment needed to do the job, you'd end up with the front element having a different refractive index than it had before you started.

But small scratches to the front element of a lens often don't matter much. I've seen lenses that have looked horrible, but that still made a perfectly fine image. Flare can be a problem, indeed as it can be with a unblemished lens, but can be controlled to a large extent with a lens hood. What have you to lose by shooting a couple of frames with the lens? You may be pleasantly surprised.

 

[glbeas]

If a scratch is large enough to cause significant flare it's large enough to fill in with India ink or flat black paint. Very careful application with a toothpick or a fine sable brush ought to do it. It does't usually affect the transmission of light enough to cause any exposure loss.

 

[nsouto]

Here is something very unconventional, but it's helped me get back many old lenses.

Pick up a *small* amount of some petroleum jelly (vaseline for the non-US folks) on a kitchen paper napkin and rub with circular motion on the front element until well spread.
Then pick up the paper napkin roll and start tearing off pieces, use each to clean the jelly off the lens element. You'll need a few "fresh" napkins, hence the need for the rool.
Stop when you stop seeing jelly "streaks" on the lens. Use a non-circular motion.

Don't laugh: it worked for me already, many times!

 

[Claire Senft]

Just a silly thought. there is a fluid sold on TV that is used to fill the scratches on eyeglasses. It is possible it works just as poorly on a lens. Before doing anything else take some photos and determine how well the lens performs.

 

[michaelbsc]

Not only take a few pictures, but if your performing an experiment please give us data. I really would like to see how it looks now, how it looks afterward, and find out what you did to get the result. MB

 

[Phillip P. Dimor]

I've a petzval with a very deep scratch, about three 'lines' 1/4" long and very close to one another. It's right in the middle of the lens. The lens has a bit of flare but it's still quite usable. Really though, I don't notice the scratch much.. unless i'm examining the lens.

As far as removing scratches, perhaps an astronomer buff could chime in; they do some amazing things with glass..

Perhaps like removing scratches from silver with several grades of abrasive? *shrug*

 

[Claire Senft]

Removing the scratches with the use of an abrasive could change the curvature, would change the thickness and might result, even with very careful and highly skilled work, in making things worse.

 

[nsouto]

Absolutely. Any abrasive is a no-no, in my view.
The vaseline thing works by allowing very gentle "smudging" of any marks or scratches of the coating.
Goes without saying: only for coated lenses.

I wouldn't be game to use anything remotely more abrasive! Although there might indeed be some varieties of pumice used to make telescope mirrors that might work.
But they will inevitably change the curvature of the lens, with dire consequences.

 

[Bob-D659]

In theory, you might be able to fill the scratch with a UV cure optical cement and that should reduce any flare caused by light diffracting from the scratch. I somewhat doubt that it would give any better results than filling the scratch with india ink. Trying to polish it out is a waste of time, you will just change the focal length of part of the element.

 

[michaelbsc]

In theory, you might be able to fill the scratch with a UV cure optical cement and that should reduce any flare caused by light diffracting from the scratch. I somewhat doubt that it would give any better results than filling the scratch with india ink. Trying to polish it out is a waste of time, you will just change the focal length of part of the element.

Since the thread began and the suggestion about India ink came up I've been thinking about it quite a bit. Frankly it seems that this is by far the best idea without spending a fortune on having the lens reworked by a real optical shop. It's probably cheaper to find another one on some auction site than do that.

Have you actually done this? And it works well? Unless the gouge is large it seems to me that this won't reduce the f-stop appreciably, and it should certainly be less flare than leaving it alone.

My "guess" as a total optical layman is that any kind of treatment that still allows light transmission will fail to match the refractive index of the remaining coating/glass and degrade the image by slight fringing, while simply obliterating the damaged section of the lens will merely slightly reduce the effective aperture.

Am I analyzing this correctly, or is there something more complex that I fail to understand.

MB

 

[CLee]

Thanks all. I'll have to do some shooting to see how bad it actually is.

 

[John Koehrer]

I've used gloss black paint to fill in some mighty bad front element scratches. A #5/0 brush with some of the bristles removed works.
If you can find another (inoperative)lens, swap the front element.

 

[Tusker]

GLASS REPAIR??

I have never had this done, but how about these windshield repair outfits?? As I said, I don't know how they work/, but stranger things have happened. Just one reason I have always kept a filter on. It might work?

 

[budrichard]

A defect in a lens does not image as a defect but can only effect the resolution, contrast of the lens as each area of the lens has some part in the imageing.
Before doing anything, test the lens.
Anything other than a new element is usually not worth the effort.-Dick

 

[michaelbsc]

A defect in a lens does not image as a defect but can only effect the resolution, contrast of the lens as each area of the lens has some part in the imageing.
Before doing anything, test the lens.
Anything other than a new element is usually not worth the effort.-Dick

It took me a long time to wrap my head around the fact that "all of the lens" was responsible for "all of the image" in a way that made sense. That's why a "spot" or dust on the lens doesn't show up as a spot on the image. (If you're having trouble with this, think about the fact that closing the aperture to "delete" the edge of the lens reduces the vignetting of a cheap lens, i.e. adding the edges of the lens into the equation causes the edges of the image field to be dimmer in relationship to the center of the image filed. So the outside edges of the lens add more light to the center of the image than to the outside edge of the image circle. Weird, but true.)

That's also why I would theorize, although I'm sure some guy who understands the math of lenses could perhaps confirm or deny, that anything you do that involves changing the refractive index of the lens affects the image. Obviously the scratch has an effect if it can transmit light, specifically it will increase the flare over the entire image field. And I *THINK*, but can't say for sure, that anything you do the lens that transmits light will also have a different refractive index than the glass/air boundary and contribute to flare. Perhaps if the refractive index is close to the glass/air index it may be better than the scratch, but I'd have no way to predict that.

It does seem to me, perhaps incorrectly, that the black paint idea only obliterates that portion of the lens's contribution to the image field and, as such, is like a decrease in aperture diameter rather than a contributor to flare. It's more like a gigantic speck of dust rather than something that transmits light to the "wrong" places because the refraction is wrong.

Is this right? Close but not quite right? Or boy, hello stupid, you missed the boat?

MB

 

[glbeas]

You've hit the idea squarely in the head! The paint solution poses the least interference in the optical properties of the lens of all the proposals.
The less you have to do the better.