Lenses and Optics

Front Element Scratches

Published October 30, 2008

We had a chance to make a pretty fun demonstration today, and here it is. As most of you know, we’re very finicky about our gear. We don’t like even tiny scratches on front elements or dust in a lens (although a bit of that is inevitable). We’re like you. We want the lens to look as good as the pictures it takes.

That said, its amazing how much dust or how many scratches a front element can take without significantly impacting image quality. Here are a couple of images taken with a lens with a fairly bad front element. You’ll notice they’re a bit soft and underexposed, but there’s no ‘image’ of the scratch, just like a dust particle can’t make an image on the sensor: the light bends to much through the subsequent elements for the dust or scratch to be visible in the image.

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And the lens that took the images above:

front-element-broken-lens

As you can see, scratches and lots of dust in a lens may cause loss of contrast, loss of light gathering, and lens flare, but even so, will not be visible on the image. (In fact, our guess is most of the lost sharpness is because the optical element shifted when it broke, rather than from the cracks themselves.) Dust on the sensor may show up on an image, but a bit of dust within the lens or scratches on the front element really aren’t something to worry about.

As a couple of people pointed out, that shattered lens did behave completely differently when we stopped it down and shot into the sun. The next shot is backlit by angled sun, stopped down to f/7.1, and a pretty refracted rainbow shows up, along with a further loss of contrast. The last shot is directly into the sun, which would cause some flare with any lens, but nothing like this 🙂 By the way—one interesting thing was when aiming into the sun the lens lost the ability to autofocus entirely, not surprising I guess when you see the final image.

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Roger Cicala
Lensrentals.com
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Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Lenses and Optics
  • Michael Clark

    Because I’d rather not have to deal with the reflections off the flat surface when it’s not necessary. Why would I put myself in that position when I can shoot without the filter and still not scratch the lens?

    I’ve had my EF 70-200mm f/2.8 L IS II since 2010. I’ve shot sports (football, basketball, soccer, etc.) from the sideline (which can be a high risk environment), in all kinds of weather, used it in packed concert halls and arenas shooting concerts, etc. I’ve cleaned the front element plenty of times when needed. It’s never had a “protective” filter on it. There are no visible scratches on it. The hood, which does have plenty of scrapes and even a couple of paint marks, does its job protecting it very well.

  • Super Keith

    Protective filters can be had for under $20. Sure, you can still have an effective lens with some minor scratches, but why would you even put yourself in that position if you can protect it for less than $20?

  • Michael Clark

    It could also be argued that this information supports that it is not worth spending hundreds of dollars on “protective” filters for each of your lenses that have a detrimental on image quality in order to prevent the occasional light scratch.

  • Michael Clark

    There’s a time and place for using “protective” filters, but they are much rarer than most folks think: Sandstorms, Ocean spray, Industrial environments that involve welding, grinding, cutting, etc. in which microscopic pieces of hot metal or sawdust are flying through the air, and so on.

  • That’s dust in the lens. Usually an expensive dismantle of the entire lens internal mechanism to get it out. I also received a Canon EF 24-70mm f4 USM IS in this condition and sent it back.

    Decided I didn’t have a use for a lens that big and slow so I didn’t replace it. The f4 zoom rates out at 4 t-stops and the f2.8 zoom rates at 3.3 t-stops at dxomark – both are really slower than what I like. Colours were gorgeous and transparent though, very detailed resolution, best of what you expect from Canon.

    Moral of the story – don’t accept this in a used lens. If it’s a new lens, send it in for repair immediately so you can’t be blamed for the dust and denied warranty repair.

  • I know I’m super late but they mean the fluid from a Compact Disc (CD) cleaning/restoration kit.

  • Max

    Correct. I can see the little nick on my Fuji X100s’ fron element in the bokeh balls, and that’s pretty much it.

  • Leandro Barbosa

    Hi Roger, https://uploads.disquscdn.com/images/5282c779470b36e1db34f4846f1cc55d722f6dcb715cad0d6ab38b339070ab2c.jpg
    How are you?

    My name is Leandro and I’m from Brazil.

    I would like some help with one doubt about a bright dot into my lens.

    I bought a Canon 24-70 and I found a little bright point in side.
    I can see this little bright point just of one angle.
    When I change focus the point moves too.
    I should worry about this? M

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