Front Element Scratches

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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.

And the lens that took the images above:

Lens with shattered front element

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.

Roger Cicala
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25 Responses to “Front Element Scratches”

bernvern said:

I have had a small scratch on my lens when I leaned over a stone parapet and the camera sat on the edge of the parapet, lens down, I have used a CD correction fluid to put a small drop on the scratch to UN sharpen the edges of the scratch. Seems to work a treat. The only hassle is when I clean the lens the drop has to be replaced but at least I dont get bright reflections off the leading edge of the scratch when the sun strikes it.

Walt said:

+Sammy I was a lot like you when I first started since I read somewhere I should put a uv filter on all my lens so they wouldn't get damaged. Only problem is a filter - and it will depend on the filter - reduce the image quality by requiring light to pass through an unnecessary layer, and they also introduce flaring and vignetting.

When I store a lens I put the lens cap on it, but when I'm out shooting, I just have the lens hood on it. Story, but unless you are using a filter for some type of effect in your shot, you really are limiting the quality of the photo you are about to shoot ... and - IMHO - you are wasting money.

Julian Jackson said:

Ha, there I was googling to find out whether my newly acquired (and very old) Ross 183mm lens for my 5x4 MPP was likely to cause any image issues (hadn't noticed any btw)...why? ...because it has a very small surface chip.
Truly awesome stuff, Roger!
Made me wonder..as you said it was a demonstration, did Roger trash the lens on purpose to check the theory?!

Spongefinger said:

I have some nasty deep scratches on the front element of my 70-200, i never really shoot above f8 and it has never impacted on any image and i shoot a lot with this lens.

Fab said:

"The more the lens is stopped down, the less you’ll notice front element defects/damage because of diffraction."

No, it's the other way around. Field of view is much more relevant than diffraction here.

Alex said:

Hopefully this article will never scroll off the archive. I refer people to this article on a regular basis. A couple of years ago I damaged a lens, and never would have thought to even try it, had it not been for this article.

stevenk said:

The more the lens is stopped down, the less you'll notice front element defects/damage because of diffraction.

rus said:

Where are pictures? :-(

free PSD templates said:

Curious how the lens craked like a star. That tells something about the structure of the glass, I believe. thanks a lot for this review!

Brian Ji said:

And this is why I almost always buy used lenses. Often there is little dust and small scratches that will never show up in any photos. A good way to save some cash for other lenses.

Mihai said:

Wt*... pictures this good(not horrible) with a cracked lens and I sometimes get a small underexposed patch from a tiny scratch? wt**** ?

Bearfoot said:

And this, my friends, is why camera equipment is so *censored* expensive.. :)

Neat article.

Sammy said:

Lens Filter Help, the filters are not to protect against major failure. If your front element is going to receive a sharp blow, your lens is going to be history. Filters protect against minor scratches due to small knocks or heavy cleaning, finger marks, dust and rain. Using one means you seldom have to clean the front element of the lens itself.

This page is being referenced by some to support the position that scratches don't matter. I think it clearly shows that they do matter, but that they must be extreme to be worth getting worked up about. In other words they are still to be avoided and minimised but there's no need to spend hundreds of dollars fixing or replacing a lens over a small scratch.

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