Technical Discussions

Bad Times with Bad Filters

Published October 16, 2013

A long time ago I wrote a blog post called Good Times with Bad Filters about how cheap UV protective filters are different from good ones. It was mostly in fun.

Today I’ve got a post about how cheap UV filters may hurt your lens. It’s not in fun.

Here at Lensrentals we see lenses come back with scratched front elements every so often. Not a big deal, it happens. But since the Canon 24-70 f/2.8 Mk II lens came out we’ve seen a whole lot of them come back with scratched front elements. The weird thing was it was always in the center of the lens and often circular in pattern like the one below. (Ignore the dust, this front element had been taken out for replacement and sat on my desk for an hour before we took the picture.)

 At first I thought maybe there was a problem with the new coating Canon was using, but it seemed a coating issue wouldn’t occur just in the center.

It turns out that the combination of the slightly bulging front element of this lens and a ‘less than best quality’ thin or ultra-thin filter is the culprit. Let me make this point first, though: The vast majority of filters do NOT touch the front element of this lens. I went through a number of filters before I found one that did. But it can happen and that’s worth knowing.

This 24-70 had a front element that was about to be replaced because of some scratches near one edge (which is why I didn’t mind putting filter after filter on it to see if any caused a problem), but the center was absolutely clear.

 I went through 8 filters with absolutely no issues. The 9th filter, though, seemed to come in contact with the front element. It’s hard to be certain about that by just looking and feeling. So I dusted on the back side of the filter with a little carbon black. Notice I covered a fairly large area of the filter with it.


Then I put the filter on the lens, took it back off the lens, and took a picture of the front of the lens. Notice the circular pattern of the carbon,which is fairly clingy. Other than a few specs, it doesn’t come off the filter except where there was glass-to-glass contact. This is a much smaller area than the large smear of carbon I put on the filter.

And when we blew the carbon off the lens, there were a couple of scratches that hadn’t been there before.


This is a good demonstration about what MIGHT happen. I will add that I’ve put another dozen brand name filters (Heliopan, B&W, etc.) on this lens with absolutely no problem and no sign of glass-to-glass contact. It seems that you need the proper combination of a thin-line filter with glass close to the back of the filter, and a lens with a slightly bulging front element (this lens has one, but so do lots of others) to even worry about it. I would also think that wider front elements (this is 82mm) might allow more play or sag in the center making this more likely.

For those of you who can’t wait to go post something about how the Canon 24-70 f/2.8 II has a problem, let me assure you that’s not the case. I had to try a number of filters and the one that I used in the demonstration is a ‘discount’ filter that someone sent back to us in place of the name-brand filter we sent them. The other name-brand filters I tried were all fine.

I’ve also seen this ‘center circular’ scratch pattern on a few other lenses and we’ll start watching for it now that we know what it is. But I don’t have enough records to go back and figure out which of the numerous front element scratches we’ve seen were of this type.

My suggestion, though, is that you stay away from ultra-thin filters on these lenses, especially discount ultra-thin filters. If you look across the front of your lens from the side, you can get an idea how far up the center of the lens bulges. Then look at the back side of your filter and see how far the glass is from the bottom of the threads. If those two distances seem similar – well, be careful!

Roger Cicala

October, 2013

Author: Roger Cicala

I’m Roger and I am the founder of 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 Technical Discussions
  • Mel Snyder

    As I read this, I let loose with an expletive – I’d seen a similar circle in the middle of a new 52mm Sigma DG CPL filter I’d bought just before a 3-week EU trip.

    Upon close examination, the circle was not on the lens side of the filter. And the lens on which it had been used had a up-sizing adapter ring that assured it wasn’t touching the lens front element.

    My lens cap isn’t touching it. And yet, the circle is right where it would be if it had.

    I can’t figure out how it got there. But thankfully, it wasn’t lens contact.

    Now, if I could just figure out where I put my Rocket blowers when I unpacked upon my return home. I remember taking them out of my backpack and rollaboard. I finally ended up ordering a replacement big one from Amazon. It will arrive this afternoon, surely smoking at least one of the misplaced ones out of its hiding place…

  • Karl Perry

    Two comments here:

    1. Be careful about equating “element too close to rear” with “cheap filters.” We can all bring to mind reliable – and expensive – companies who have made poorly designed and/or manufactured products.

    2. Quite frankly I think that Canon, to reference your specific case, is more at fault for designing their lens such that a thin filter could impact its front element. What would it have cost them to design/manufacture the lens such that there is no possibility of a filter touching the front element? Answer: virtually nothing.

  • Ernst Lopes Cardozo

    I’m wondering what Canon’s specifications say about minimum space between the back of the filter tread and the glass of the filter … or is this a ‘trade secret’ to keep the competition in the dark?

  • Matt Parker

    Two years ago I had a Canon 77mm UV Filter that when installed on the Canon 24-105 would touch the front element when screwed on tight. I though this was a problem and confirmed it by, “fogging” the glass (breathing on it) then screwing on the filter. I purchased the B+W and the problem went away. Canon was absolutely no help with this when I asked them about it.

  • Frank

    Back in the 1970s when I got my first used Leica 35mm camera the store owner insisted that I place B+W uv filters on my Leitz lenses. I can’t tell you how many times these filters have saved my lenses, even with the hoods on them. I know; I try to be careful, but stuff happens!

  • It appears that everyone basically agrees that a “protective” filter may serve one well, or not, depending on the conditions while shooting, and also on the particulars of an accident. Years ago, with film, I did some experimenting. I checked various lenses with good UV filters at the time (Nikkor single-coated L37s). I found with one zoom while shooting straight at the sun that I did get a worse flare area around the sun with the filter than I did without it – but only with that one lens and not with several others of a variety of types. I also checked for edge/corner softening effects with super-wides and found no ill effects. I then used a 300mm f2.8 and 400mm f3.5 wide-open with a distant detailed target with no rear or front filters in place (refocusing, of course, when the rear filter was removed or replaced); with only the front filter on; with only the rear filter on; and with both filters on the lenses. Again, there was no detectable degradation in the image (or improvement…). I continue now with digital cameras to use both UV filters (AND shades…) on lenses that can accept them (my fisheyes and super-wides can’t), but I have switched to multicoated filters with digital, going by the theory (only!) that the likely higher reflectivity of the sensor compared with film *could* introduce more problems with reflections back through the lens to the filter with relatively very bright light sources within the image area. I prefer to clean a filter than a lens – and the filter did save a lens from being scratched when someone grabbed my lens (I tossed the scratched filter and replaced it).

  • jojo

    Is this a problem with the filter or lens? I.e, should the lens not have a bit more distance between the tip of the element on the thread (i.e, make the barrel 1/8 or 1/16 inch longer ?

  • Jamo

    I should think if a filter can flex enough during cleaning or general use to touch the centre of a lens, then the typical pinch-grip plastic lens hoods that are supplied with most modern lenses could also do it. When you look at them there is not a whole lot of clearance and they are more flexible, being plastic, than the average filter element.

    I dropped a camera bag once and a filter that was mounted on a lens shattered in spite of the padding. The shards of glass scratched the front element of the lens. I’ve also bumped a lens against a rock and the filter ring got bent but the lens’s filter thread was protected…so the protection issue goes both ways I guess.

  • Ron Carroll

    I had a variation of this problem using a B&W UV filter… The threaded retaining ring that hold the UV glass into the threaded filter ring came loose. The filter glass was no longer held tight within the ring and I noticed scratches on the UV filter glass. Fortunately the lens glass was undamaged. I had no idea this could have happened and it’s made me wary of using UV filters. And it’s ironic, of course, since I’m using the UV filters to protect the lenses

  • Richard

    I thought I was the only person who used filters to protect my lenses from kids and animals. I can’t count the number of times that a dog or horse has licked, nuzzled, or even gently bitten my Nikkors. Slobber is very hard to remove.

  • Dan Nelson

    I have been an avid photographer for 20 years and the only time I got a scratch in the front element was from a “protective” filter. I bumped the filter ring from the side, the filter shattered and drove sharp filter glass into the front element. That was the last time I ever used a “protective” filter.

  • Benjamin Anderson

    I have UV filters on most of my lenses to protect them from animal noses and children’s finger prints. I’ve not as concerned about a slight scratch on a filter if I need to use my shirt to clean off the filter in a bind. But, my EF 16-35mm f/2.8L isn’t completely sealed without a filter, so in that case, it’s a significant improvement over using the hood has a buffer.

    The UV filter has also saved my lens too, since a good one will also provide a strong additional metal crumple zone. I forgot to grab my 7D one afternoon after lunch, I placed it on the roof of my SUV while I put my daughter in her carseat, and drove off. The camera flew off the top of my truck during a 70-0MPH stop and landed 10ft in front of the truck in the middle of the intersection. Surprisingly everything other than the UV filter survived the accident, but the lens wouldn’t have without the filter. The filter took the blunt of the tumble after the lens cap and hood popped off the moment the corner of the camera hit the concrete.
    As a result, I don’t rest anything on the roof while I load things up any more. But after cleaning up the lens and getting of the glass dust out, I bought a replacement UV filter.
    The 7D now has some scars, and the weather sealing is a little questionable since the seams bulge a little, but both the lens and camera are still fully functional. Had it been my 5D MKII, which usually has my 24-70mm attached to it, it would have been a completely different story though.

  • Big Hank, I think Franks suggestion of the lens hood is a good one. I have dinged my lens hoods a number of times and protected a lens probably better than a uv filter would. This also adds to the IQ instead of taking away from it.

  • BigHank53

    Frank, I’ve seen filters save two lenses within the past year. One was mounted to a camera that swung (on a neckstrap) into a rock. Now, there was a bit of luck in the fragments didn’t scratch the front element…but the rock definitely would have. The other one was a Panasonic zoom that I dropped. I bent the filter ring instead of busting the plastic filter threads on the lens.

    I’m not going to tell you the methods you use are wrong, because they’re not. But I’m a bit of a klutz and spend a lot of time scrambling through the woods, so I think I’ll keep using filters.

  • Frank Kolwicz

    I’ve always felt that the use of filters for “protection” of the front element was bogus: why would having broken *glass* jammed into your lens be better than some random environmental substance? As to protection from scratches, most of those are probably from cleaning, so just learn to clean properly, unless you are necessarily working in a seriously dirty or corrosive environment where keeping the lens clean is impossible – then it makes sense to use a filter for protection and also putting your camera/lens in some kind of protective bag or box.

    A hood, rubber or plastic, is better protection against dropping than a filter and a lens cap when not actively shooting is better yet – put it on and take it off, if you really want to protect your lens, because you’re more likely to damage your lens when the camera is not in your hand and up to your eye.

    “Creative” filters may be necessary for some uses, but, of course, you wouldn’t leave one on all the time, where’s the creativity in that?

  • Roger Cicala

    It’s not that simple. Some brands make a dozen different ‘labels’ of filters to different specifications. Other brands have subsuppliers that make their metal rings and may change the specs slightly over time. And there are dozens of brands, only a few of which I have on hand. Of what I tested Heliopan and B&W did not scratch this lens. But that’s not an absolute guarantee no Heliopan or B&W would. The tolerance is pretty close even with those and someone emailed that theirs doesn’t touch but if they clean it with a cloth while mounted they ended up pushing it in to where it did touch.


  • EricK

    What brands and type of filters did not scratch the front element?

  • Roger Cicala

    Hi Tom,

    We probably didn’t notice it back then. I think we started tagging batteries a little over a year ago.

  • I rented a 5D MKIII about two years ago. I had my brand new 7D as a backup body. I used both Batteries in the 5D, and ended up returning the wrong battery with the 5D. I figured it out months later when I bought a lens and it had the same little dot on it. I think you guys got the better end of the deal on this one. I would rather have kept my battery though, but honestly didn’t think about it. If I would have not been rushing to get the package back to the UPS store, I might have been more careful. It probably wouldn’t have been a bad idea to mark the battery with a very visible mark that you could see when you open the battery compartment up. I do apologize for the swap though. I’m not a deadbeat, just tired and constantly distracted. Another very informative article. I would think a thin circular polarizer that constantly spins would be another likely culprit. I think I would faint when I figured out I just ruined the front element.



  • Tortap

    Have you tried different filters with Imatest or your optical bench? That would be an interesting read I would think.

  • Roger Cicala

    Nancy, we do not send out lenses with filters – it’s only by customer request. The ones we’ve had scratched weren’t sent with filters so I assume the customers used their own.

  • NancyP

    Ack! Now I am worrying about my B and W thin Kaesemann CPLs. I don’t bother with UV or clear filters for most lenses, assuming that the hood should be reasonable protection against bumps. Do you always send out the lenses with UV or clear filters for protection?

  • Roger Cicala


    Most of the time when we ask them to swap back, they just swap back with us. Some get nasty, but not many. If they made a mistake, we ask them if we can bill them for the missing filter / battery and send theirs back. If we can’t come to some reasonable agreement, we just eat the costs – once. But if it happens more than once we won’t do business with that person anymore.

  • Otm Shank

    Or just bill them for the cost of replacing the battery and/or filter.

  • Aaron


    So do you just not rent to those people again? Or do you give them a warning and if they keep doing it you blacklist them?

  • Roger Cicala

    JF, you want to see the big pile of old batteries people sent back instead of the nearly new ones we sent them? Of course they didn’t realize our batteries are tagged.

  • This is seen with other lenses as well. For example, the EF-S 10-22 lens bumps into the very own Canon (non slim) filter.,
    and I have seen more such reports, though never as bad as your example.

  • JFGilbert

    “..a ‘discount’ filter that someone sent back to us in place of the name-brand filter we sent them.”
    I don’t think I would last long in your business. My tolerance for dishonesty and stupidity does not stretch far enough. I admire your ability to leverage this “swap” into something useful.

  • Scary post, and I’m sure the replacement front element can’t be cheap. Thank you for yet another cautionary tale like the Color Run article.

  • This type of investigating and information gathering is a large part of why, as I’ve said before, I rent exclusively from Thanks Roger!

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