Lens Scratch Test, Canon

2009/5/16 (Saturday) | Filed under: How To/Tech

70mm, f5, 1/250, ISO 200, with post-it stuck to lens

I have been reading some interesting stuff lately about how today’s lenses with modern materials are harder and tougher than the ones made 10 or 20 years ago. One article about lens scratches actually challenged the reader to stick a small corner of a post-it note to the lens and observe the effect it has on your photos. Challenge accepted.

Here is my lens (Canon 24-70mm f2.8). I don’t use UV filters to “protect” the lens except in extreme situations. Who wants to buy a big expensive lens and stick a basically clear filter over the front of it anyway? UV filters won’t enhance your image accept in extreme cases such as high elevations on very clear days where excessive UV light is present. Your image sensor already has a built-in UV filter for normal situations. I am not too worried about the adhesive of a post-it which is not that strong and will surely come off easily with some lens cleaner and a swab. It was time to clean my lens anyway and the post-it will only be on there for 15 minutes or less.

Keep in mind this post-it is BIG. If you had a scratch this size on your lens you’d be freaking out right?? Plus a scratch on glass is presumably translucent, not totally blocking light like a post-it.


Simulating a big lens scratch.

The flower shot at the top was made with the big ‘ol post-it stuck to the lens. Same with the bunny below.

Trying to take an everday scratch test picture - Everyone likes bunnies right?

Trying to get the scratch to show up.

57mm, f7.1 @ 1/500, with post-it stuck to lens

57mm, f7.1 @ 1/500, with post-it stuck to lens

The bunny was shot at 70mm, f8. Now, here is where I get into trouble. I had to really work hard to get this one below—


f11, 24mm, 1/400 - finally we can see the post-it!

Had I put my camera in automatic mode and shot normal “every day” stuff, it may have taken me 1000 photos to get the “scratch” to show up.

I shot a bunch more with the post-it. The “scratch” was evident only beyond an aperture f11, and only at the shorter focal lengths like 24mm (zoomed out, as opposed to zoomed in). Shooting at 24mm. At 57mm, f7.1, for example, I could not detect the slightest hint of the post-it even when viewing my file at 100% magnification in Photoshop. I experienced the same result at 24mm, f2.8 (zoomed out and wide open).

One side note: You’llĀ  notice some blotches in the top right of the frame in the sky. Those are caused by dust on the image sensor. Honestly, I seldom clean my sensor because it is hard to get these to show up in most every day situations as well. Dust shows up when shooting very small apertures like f11 and beyond, and its easy to fix in Photoshop. It is easier than cleaning a sensor in my view.

The moral of the story- stop worrying about tiny scratches on your lens!! If you shoot every day auto-mode stuff for the most part, or even some advanced portrait and wedding type stuff, you’re not likely to harm your photos AT ALL. If you’re a landscape photographer with experience, you probably find yourself zoomed out to the wide side of your lens and stopping down to small apertures manually quite often and you have a little more cause for concern.

If you’re shooting in a sand storm, it will not hurt to throw a UV filter on your lens just in case. For the most part, I do not advocate protective filters.

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  1. phew! that took a load off my back. Thanks Rob! You’re the first person I know who doesn’t advocate the use of protective filters.

  2. I don’t use them either for the same reason. Expensive lens + cheap filter = not my way of shooting. Besides, it’s one other plane of glass to clean. Good post, dude.

  3. Nice info. I stopped using filters years ago. I remember seeing a post where the guy had REALLY scratched up the lens and the quality was still fine. So best not to get too het up about the odd little scratch!!

  4. I thought my lens was dirty, since my dog licked it when trying to get close ups, but the following pics were great. No sign of streaking or anything. These lenses are amazing and just in case, I am going to buy the lens cleaning kit.

  5. My dog licked my lens when trying to get a close up, and alas nothing appeared in my pictures following, however I will still buy the lens cleaning kit just in case! These lenses are amazing!

  6. Sorry, but this is dumb. You don’t buy a cheap filter for an expensive lens. You buy a $100 B+W filter.

  7. Sure, I guess if the filter is DOING something for your images, go ahead and get an expensive one. Or are you just buying a $100 dust cover?

  8. Filters are cheap because they are simple flat pieces of glass. $20 is about all you need. And if you are concerned take it off, then put it back for the family vacation shots.

  9. ….and why do I need a simple flat piece of glass over my lens for family vacation shots? The lens hood is plenty of protection for me unless there is a sandstorm or something. My point is, I’m not going to use a filter unless its somehow enhancing the image or affecting the exposure, like a polarizer or an ND filter.

  10. I use a good quality UV filter, but more for retaining the re-sale value of a lens. People who buy “used” lenses are often paranoid about everything from dust to scratches and everything in between. Telling them that a UV filter has been on the lens the entire time helps abate those fears. However, this post and others, illustrate how much it actually takes to denigrate an image!

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