Living with Photography: "The Mechanical Prophylactic"

By Norman Chan

Testing a cheap and expensive lens filter, and then considering whether a UV filter is necessary at all.

Apologies if the title of this week's column is a little crude--it's attributed to Ken Rockwell, a no-nonsense photographer who gives very useful practical advice about gear and techniques on his site. In this case, Rockwell was referring to a UV lens filter for DSLRs, which he says doesn't have any optical benefits for today's cameras. It's a topic we've broached before--whether or not a UV filter is necessary at all. Photographers are split into two camps in this debate.

The first camp believes that UV filters not only are optically useless, but unnecessarily degrade the quality of your images. Putting a piece of flat glass, no matter its build quality, on top of a $2000 lens is going to affect the quality of light hitting the sensor. UV filters were originally designed to block out wavelengths of light that can't be perceived by the human eye, but affect film. Ultraviolet light on film can leave a haze effect and reduce contrast, but this effect doesn't apply to modern digital cameras, which compensate for UV in the sensor and image processor. So for DSLRs, the purpose of UV filter is now primarily to protect the front element of the lens from any potential damage. In fact, when you buy a UV filter from a company like Tiffen, the image on the box shows a cracked lens--the manufacturer doesn't hide behind the fact that UV filters aren't really for UV protection.

But damage protection is exactly what the second camp feels is necessary about using a filter. That extra insurance against dropping a lens element-first into the ground warrants what they consider negligible image quality loss, which makes sense if the camera is being used for web photos or is equipment on loan, like shared office equipment. UV filter users believe that lens resale value is higher with a UV lens, too. It's the photography equivalent of putting a plastic screen cover on your new smartphone.

With my two lenses, I wanted to see for myself not only if having a lens filter/protector significantly affected photo quality, but also if there were any noticeable differences between a cheap UV filter and a more expensive one. I bought two filters to test: a dirt cheap $9 Tiffen UV filter, and an expensive $70 B+W UV filter with "multi-resistant coating". But as of today, I'm ditching the Tiffen filter and going to use the B+W filter on new lenses.

Image artifacts first showed up at Maker Faire, where photos taken bright daylight showed some pretty gnarly artifacts. I wasn't worried about the possible vignetting on the photos, because that can be easily fixed in Lightroom (and I actually like the look of a little vignetting). The two major problems with using a cheap UV filter are flaring and ghosting, both of which can be seen in the photo below.

If you look near the top of the steampunk Nautilus vehicle, where Will is standing, you can see two overlapping ellipses superimposed on the rim of the Nautilus shroud. That's the effect of ghosting, which is when light bounces between the lens elements and filter and then onto the sensor, which sees the reflections in focus. That effect also contributes to flaring, which can be seen as the streaks of greenish light coming down from the top of the frame masking the subjects. You know how video games and movies often try to simulate lens flare? This is the real-life optical effect, which is much less cool and effective than JJ Abrams makes it look.

Ghosting and flares with the Tiffen filter were accentuated with my wide-angle lens--I could actually see the ghosting warp and stretch as I zoomed in and out. It's most likely to happen when you have a strong light source, like the sun, at the edge of your frame, since it's hitting the curved lens element of a wide lens from a tangent and not straight on.

That's not to say that the B+W filter is completely free of these artifacts, either. In the comparison below, the left-most image is from a lens with no filter, the one in the middle is with the B+W, and last image is with the Tiffen. You can see that even with a $70 filter, a ghost ring faintly appears where there is none in the filterless shot.

So why use a UV filter at all? I'm caught somewhere between two sides, since I'm a sucker for getting the best image quality possible. But the paranoid part of me still worries about dropping a lens, or somehow scratching the front element during cleaning. The option of using a lens hood as protection from falls seems silly, since it's more cumbersome to have a hood at the ready at all times. It's likely that I'm still in this honeymoon period with my gear, and am being overly cautious about it when it's only a few months old. What's more likely going to happen is that as I get more comfortable juggling lenses, I'll only keep the nice B+W filter on the newest lens or the one I use the most, taking it off once the newness (and accompanying coddling) wears off.

Once again, not too many entries for this week's photography challenge in the Tested Flickr group. I admit it's tough to keep up with weekly challenges, so would like to propose something simpler: let's just keep the knolling challenge an ongoing endeavor, and I'll call out the best ones every week. Remember, knolling can happen anywhere, and with any number of items! Let's take Adam's quirk and just run with it.