During a nice nature trip, sitting at a table with a bottle of wine, somehow we had the ridiculous idea to test a lens as burning glass (which performed quite well).

After we went home I started cleaning the lens and noticed a small curly path inside the lens, which I image could be the scars left from an intense heat beam damaging the lens’s guts, like some coating or other damage-prone surface.

So, is it possible that the immature act to use a lens as burning glass forever damaged the optics inside, or could it be something else?

(Stupidity left aside, it ain't some heavy glass lens, but a third-party prime, and quality seems untouched, so I don't really bother.)

Edit: So here are some pics. Didn't have a macro lens available though:

Lens1 Direct Link

lens2 Direct Link

lens3 Direct Link

By looking more closely to it, it could be a small filament of some sorts. It really is inside the lens, I guess between the front and the second element. Impossible to get a precise side view as the image gets distorted by the front element. On the second picture you can even see a rainbow pattern on it as the light gets dispersed.

Also, it's almost invisible. I had to highlight it with a LED light from the side to to have it come out like that (like a scratch in a glass surface would).

  • 6
    \$\begingroup\$ Can you post a picture showing the lens? Or describe the apparent damage in more detail? \$\endgroup\$
    – mattdm
    Commented May 16, 2011 at 11:02
  • \$\begingroup\$ Good Idea, I'll try to. \$\endgroup\$
    – Berzemus
    Commented May 20, 2011 at 8:38
  • 3
    \$\begingroup\$ Are you sure this is not a strand of lint or something that you just now noticed? \$\endgroup\$ Commented Oct 26, 2013 at 3:40

4 Answers 4


I would say at least for most practical purposes the answer is no.

First of all, you only get intense heat where the light comes (at least close to) in focus, which does not happen inside the lens.

Second, you only get heat when the light is absorbed -- but a typical lens transmits virtually all the light, which translates to absorbing essentially none of it. A lens can't absorb any significant amount of light and still function even reasonably well as a lens.

  • 4
    \$\begingroup\$ actually some energy in the non-visible parts of the spectrum (specifically infra red and ultra violet) is indeed absorbed by the glass and coatings. \$\endgroup\$
    – jwenting
    Commented May 18, 2011 at 11:18
  • \$\begingroup\$ The biggest risk is contamination on the outer optical surfaces, perhaps from the combustion that was caused. The usual cleaning recommendations apply. \$\endgroup\$ Commented Mar 3, 2016 at 16:33

I think it is highly likely whatever you are seeing was already there before your experiment. The reason you are noticing it now is because you were looking at the inside of the lens far more critically than you were before.


Here is my theory

When kids use a magnifying glass to burn ants in the park its one piece of glass

A camera lens is made of many elements of glass - so when the sun hits the first piece of glass it could be burning the second or the third element or the coating

That’s my two cents worth - might be possible to get the lens cleaned or repaired by a professional.

Sounds like a cool thing to try, for sciences sake did whatever you were burning burn quickly?!

  • 1
    \$\begingroup\$ plus, if I'm not mistaken, the modern lenses are made of some sort of plastic or another organic polymer and not of glass, which makes it even more sensitive to the heat damages. \$\endgroup\$ Commented May 19, 2011 at 10:08
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    \$\begingroup\$ Kids burning ants with magnifying glass should be punished. And no, the elements cannot be damaged, see Jerry's answer. \$\endgroup\$ Commented May 31, 2011 at 9:14
  • \$\begingroup\$ A camera lens does not tend to FOCUS onto internal elements or their coatings... \$\endgroup\$ Commented Jan 16, 2019 at 2:46

There might be some damages internally incase of any plastic parts. Not sure about the internal construction. But yeah, definitely not a very good thing to try. But as for the glass the coating maybe damaged but I'm sure nothing would have happened to the glass. They definitely are made to last.


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