Tuesday, September 22, 2009

Using Filters to Protect Your Lens?

When you buy a new camera with a lens or a new lens and you are buying it from a local shop, they will ask you to buy a UV filter.  Often the more experienced and jaded photographer will tell you that this is just a ripoff and you don't need the filter.  Yet the salesperson will tell you the story about the time the lens was in a sand storm - dropped or pooped on by a bird and the filter saved the lens!  Better to lose a $30 piece of glass rather than a lens worth hundreds.  So what is the truth?  Answer: they both have a point.

For a person who is buying their first DSLR, a protective filter is probably a good idea. Especially of Children's fingerprints are an issue! :-)  But, it should not be a UV filter.  The digital sensors on your camera are already protected with a UV blocking filter!  If you feel that a protective filter is needed get one of the clear filters that is designed for digital cameras.  They are specially coated and are designed to minimize flair and ghosting.  And don't get the cheapest.  I use B+W filters when I do need one.  They are not cheap, but they are not going to affect my pictures as much as that $20 un-coated filter from some no name company. 

On the other hand, even a great filter has the potential of affecting the image.  After all, it is an additional piece of glass added to a lens that was not originally designed for it.  Thus many of the pickier Pros don't even use them.  As protection to dropping, a good rigid lens hood will do as good a job - if not better - as a protective filter.  However, many of these same pros use Circular Polarizer(CPL) filters a lot and they can doubles as additional protection anyway.  So, barring your lens getting licked by your 5 year old, you lens is probably protected just fine by your rigid lens hood.

In the middle of this is the reality that in extreme situations (think a wind storm in a desert), many pros will use a filter.  It just makes sense to protect your gear in extreme situations!

So the answer is clear as mud, right?  Don't sweat it.  When you buy that first camera, get the filter, but make the sales person really happy with you and tell them you want a good clear multi-coated filter designed for DSLRs.  Yes it will cost more, but it will be the right piece of equipment!  At the same time, get a CPL and you will be thanking me later when the water looks real and hte glare is all but gone... (more on this in another article).  And yes, as time goes along, the Protective filter will be used less and less as you learn to care for your equipment properly.  So, don't sweat it and let the "experts" argue the nuances of the issue.  Do what is necessary for you to enjoy your photography!


  1. Very interesting post. I'm exactly the person you describe: bought a DSLR and immediately bought a Hoya UV filter - and a Polarizing filter too. I did some tests yesterday and I do think that UV filter is knocking off a tiny bit of sharpness.

    Quick thought on using a circular polarizing filter as added protection: on cheaper lenses the filter mount will rotate as the camera focuses, so you'll be forever adjusting it. Also, my Hoya CPL cuts a significant amount of light regardless of angle...

  2. I was hoping that your post had resolved a longstanding issue I've been wrestling with: high-contrast bloom/flare/purple-fringing especially in night shots. Here's an example:


    Notice all the light sources have bloomed over the surrounding areas? This shot was taken a well-reviewed lens, a Canon 50mm f/1.4 USM, so I was hopeful that the problem was flare due to the UV filter, but removing it made no real difference.

    Any ideas what's going on? The body/sensor for this shot is the Canon Rebel XS; admittedly the bottom of the range. Am I expecting too much?

  3. Hey, took a look at your picture test. First thought was that it looks over exposed. Question, does the XS have a spot meter mode? I don't know about other situations, but the longer the exposure the more critical the exposure has to be. Blooming and the accompanying fringing is very common in night shots that are overexposed. Also, on shots slower than about 1/25, the "expose to the right" rule is - in my experience - not useful. If any thing try to have as correct an exposure as you can.

    With DSLRs, the f-stop is a funny thing. Think of the old film days of how tweeky slide film was vs. negatives. That is how DSLRs are today! The f/stop will vary in its effect a bit. I would suggest stopping it down some with the exposure compensation and see what happens. Also, the blooming in the background is exaggerated by being out of focus. That can be reduced by stopping down a bit for a greater depth of field. You can compensate for that by upping the ISO if you choose. Most modern DSLRs are quite noise free up to ISO 800-1600. Yours should handle it quite well.

    Try an example on Aperture priority at f/8, ISO 400 or 800, compensated at -.5. Then use spot metering if you have it and meter the shot on a brightly lit object such as a lightly covered building. Try the same thing at -1. If you can't spot meter, you might want to stop it down more if you can. Maybe even shoot in manual mode.

    At any rate, if you are getting over exposure a lot with this lens, I would take it to a local shop and tell them that it is constantly over exposing.
    Hope that this helps

  4. Thanks for the thoughts. I'll give it a try. I'll admit I snapped it in plain old P mode. It's ISO 200, 0.5s, f/1.4 (wide open). The histogram looks pretty good, but the bright lights are absolutely over-exposed, and there's no recovering them from RAW (to use Aperture's nomenclature). The XS does not have a Spot meter mode, just Evaluative, Partial and Center-weighted.

    My hunch is there's something more going on than simple overexposure since the blooming extends out into nearby parts of the image that should be dark. And then there's the purple-fringing on the edge of the blooms. I read somewhere that this purple might be due to refraction within the microlenses over each pixel site on the sensor, and so is hard to eradicate. Perhaps if I get the exposure right I can at least minimize its prominence. Any thoughts on this purple effect?

  5. OK, test results: The blooming/purple goes away when I stop the lens down to f/2 and beyond, so not that restricting. It's replaced with a starburst which I'm completely fine with. I find the SX does show noise in shadow detail at ISO 800, so tend to keep it at 400 and below.

    I've put a new test shot up which might be my low-light sweet spot: ISO 400, f/3.2 0.5s. Exposure is -2/3. All of which leaves all but a couple of hot-spots unrecoverably over-exposed, and the histogram shows most of the data off the left edge...


    ...and it goes without saying this is with the UV filter removed!

    Thanks for you help. Any other words of wisdom?

  6. Greetings from Port Townsend. The "clink" you just heard was my "protective" UV filter landing in the garbage can. My lens already has an impressive hood shielding the prime. (Fuji Finepix S100fs) And I use an impressive solid steel plate screw-on lens cap for travel. I've often wondered about what the extra layer of glass was doing to the auto focus. Put me in the "filter free" column!