03.23.11

Travel Photography – (UV) filters are for amateurs

Posted in Photography, Travel at 17:44 by RjZ

One of the first things most everyone buys when they get a new SLR camera, often purchasing them at the same time, is a UV filter. One of the reasons you buy an SLR camera is the ability to put these impressive optics on them with their giant (compared to a point-and-shoot camera) glass and the image quality they deliver. Screwing on a UV filter keeps dust, dirt, and your grubby fingers off the optic and the little jewel is forever safe, all with almost no loss in image quality.

It’s too bad that that’s only sort of true. The protection part is obvious, but why would you need a UV filter? Light, particularly outdoor light on clear days, is comprised not only of what we see, but UV light we can’t see. Film cameras used to have a particular problem with this. Glass coatings were not optimized to avoid UV and the film itself is exposed by these wavelengths, washing out pictures and blowing contrast to hell. I read that somewhere–it’s not like I ever used a film camera.

Digital cameras use sensors that are somewhat sensitive to UV, but modern lenses and coatings have mitigated the problem significantly. There is very little washout, even in a bright sky on most cameras these days; just try it yourself. Take a shot with and with out the filter and see if you notice any difference.

Camera shops don’t mention that photo-journalists throw lenses in their duffel bags, with nary a protective filter anywhere. Sure, maybe they’re not paying for their kit, but they know the drawbacks of filters too. For example, they can block some light and change the color cast of your lens. Most good filters have anti-reflection (AR) coatings, but they aren’t perfect and some light is reflected. If this light is wavelength dependent, then, at some angles for sure, your perfectly clear and neutral filter will change the color of light your camera sees. If they don’t change color cast the extra layers of glass often increase lens flair or create it when it otherwise wouldn’t be there. The metal ring around your UV filter can cause vignetting, particularly on very wide lenses, where the corners of your image are darkened or black. Sure, many people are doing this on purpose to the images they take as vignetting can often highlight the focus of your image, but it’s a feature you’d rather have a choice about then try to extract and remove later. If you’re using a polarizer—you are using a polarizer now and again, right?!—UV filters are a huge pain, as you’re really likely to remove them to put the polarizer in its place. After all, you spent all this money on a fancy camera and even more expensive lens, surely you don’t want not one, but two cheaper pieces of glass between you and your subject.

So, why, again, do so many people have UV filters on their lenses? Oh yeah, because the lenses are so expensive, the filter will keep it safe. Let me tell you my story.

I was taking my brand new SLR on its first trip abroad. I had it sitting in my lap on the plane; just in case something exciting happened while flying (if anything exciting actually ever does happen while flying, I can imagine taking pictures of it will not be the first thing that comes to mind). At one point, it slipped off my lap and onto the carpeted floor a few inches below. I leaned over to retrieve it and, with a sinking heart, heard glass slushing around underneath the lens cap.

My eyes bulged. I couldn’t imagine that the lens was that delicate, but I was new enough to cameras that I wasn’t so sure. I carefully opened the lens cap to discover that the ‘protective UV filter’ had been shattered and sliding around between the cap and lens. I carefully poured off the broken pieces into my OJ cup and discovered that the broken filter had scuffed the native AR coating of the lens. Thankfully, the damage is only cosmetic; you can’t see the scuff in any images taken with that lens, but the concern I felt for my lens was real. I can clean dust and finger smudges from my lens, but scuff is permanent.

Before you buy a UV ‘protective’ filter, I have a suggestion for you. If you don’t already have a lens hood for your lens, get one, and if you do, put that thing on your lens. All the time! When you’re walking around with your camera dangling from you neck, you’ll inevitably bump into something or someone probably with the business end of your bulky camera. With a UV filter in front, it’s possible you could shatter it and scratch your lens. With the lens hood there, even without the lens cap, the objective is safely nestled a few centimeters away from danger. My lens hoods are plenty beat up, but all my lenses are still safe. Your pictures will improve too! Lens hoods block stray light that gets to your sensor without creating an image. Stray does more to wash out contrast than UV ever did! Lens hoods come with many higher end lenses and are cheaper than a good UV filter anyway. What have you got to lose?

If you decide to buy a UV filter anyway, check out this thorough review which sheds some light on how much to spend and how much not to spend on your new filter. But remember, you’ll look like an amateur! That doesn’t matter, of course. (right…) but will it really keep your lens safe?

1 Comment »

  1. Angus said,

    May 10, 2011 at 15:31

    I thought the answer was that the UV filter up front immediately reduces in-field scattered light. The non-sequential effects might be significant in bright light (UV dispersing/scattering widely from intrinsic glass properties). The optical path length/focus becomes significantly altered for UV. The image plane sees this, and the mapping of bluer light is not perfect, and it ends up showing up on pics.

    One analogy: as we age, more proteins in the vitreous humor scatter bluer light more strongly, leading to greater eye focus ambiguity and haze while looking in bright light. Glasses that block well into the violet region of the spectrum greatly reduces this effect and provide better acuity while driving into the sun; in that case, some of the spectrum is blocked unfortunately, but the result is better vision.

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