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Living with Photography: Reading a Camera Lens

By Norman Chan

Like many other pieces of technology, the many specs of a camera lens should be valued differently, depending on your needs. Here's what I think is important.

Adopting an interchangeable camera system, whether mirrorless or DSLR, means that you have an intent to use more than one lens with that camera. Bundled kit lenses are typically good general purpose lenses, but the whole point of going interchangeable is to be able to swap out lenses for different situations and types of photos. Otherwise, you're better off with a good fixed lens compact, like the RX100 or Fuji X100. And while choosing lenses isn't as complicated as deciding on a DSLR body, there are many more lens options than camera body options. Even if you've settled between a Canon, Nikon, or Sony camera--and hence, a lens mount ecosystem--there are many categories and brands of lenses, each with different specs and specialties.

Most people starting off with a DSLR--myself included--are in no rush to fill out their lens collection. It's best to start off with one or two lenses, maybe kit lens included, and build experience from there. And in choosing those starter lenses, online guides I've read tend to use focal length as the starting point for recommendations. As a refresher, the focal length denotes the field of view covered by a lens, which is determined by a combination of the optics and camera sensor. As we've written before, 35-50mm is a good starting point for a prime lens (fixed focal length), with focal length 70mm or longer being considered telephoto and 28 or shorter considered wide-angle.

But focal length is just the tip of the iceberg for lens specs, and while it's the most defining characteristic of a lens, it's also probably the least nuanced trait. Today, I want to go over the other specs you'll find etched on the side of a lens, and the important ones that aren't.

Let's use the kit lens on the Sony camera above as an example. There are three sets of specs listed on the front of the lens--these alone will give you a good sense of what the lens is capable of. Ostensibly, the most important string of text is at the top, so let's parse its components.

  • The E in the front of the string indicates the mount type. Sony NEX mirrorless cameras (and its FS series video cameras) use E-mount lenses, so hence the E. Canon lenses will have an EF or EF-S moniker, with EF-S lenses only compatible with APS-C sensor cameras. Nikon cameras use the F-mount.
  • 3.5-5.6 indicates the maximum aperture (f number) range on this zoom lens. These numbers are correlated with the focal length range that follows. In this case, that's 18-55mm. Breaking that down, that means lens can zoom with a range of 18mm to 55mm, and the widest aperture when zoomed out is f/3.5 while the widest aperture when zoomed all the way in is f/5.6. In between that zoom range, eg. at 40mm, the widest aperture will be somewhere between 3.5 and 5.6. Some lenses have a fixed aperture throughout its entire zoom range, so you'd only see one f number on the lens. (eg. Canon's 2.8/24-70mm)
  • The last piece of this string, OSS, indicates the steading capability of the lens. OSS is a Sony term, standing for Optical Steady Shot. That differs from Sony's ASS (Active Steady Shot), which uses digital stabilization for video. Canon's optical image stabilization is denoted with the IS moniker, and Nikons with the VR (vibration reduction) moniker. Each lens maker calls their steading technology something different, and go about reducing shakiness in different ways.

Another spec that often goes unnoticed is the lens diameter, as indicated by the lone number sitting on the lens (49 on the Sony lens above, 77 on the Canon lens to the right). This indicates the physical diameter of the lens ring, as measured in millimeters. You'll need to know this when shopping for lens filters to screw in front of your lens. Lens filters merit their own discussion, and I've been experimenting with different brands and price categories. One quick thing to point out is that wide-angle lenses need relatively short lens filters, otherwise they're prone to image vignetting.

Finally, we come to the listed spec that I don't think gets enough attention--the minimum focal distance. On the Sony lens, that's the number listed on the right, but it's often not printed on the front of a lens. On other lenses, it may be listed on the side of the barrel next to the manual focus ring. This is typically printed in terms of both feet and meters. For example, the number is .82ft on the Sony 18-55mm kit lens, 1 feet on the 17-40mm Canon zoom lens, and 1.5 feet on my 50mm Sigma prime lens.

The minimum focal distance number tells you how close you can physically get to your subject while keeping it in focus, regardless of the focal length. So whether or not the Canon zoom is at 17mm (ultra-wide) or 40mm (wide), I can't get closer than 1 foot to a subject to take close-up shots. Longer telephoto zoom lenses typically have a very lengthy minimum focal distance, which is compensated by the fact that you can zoom in. You're not going to be able to hold a 200mm zoom lens right up a subject and have it in focus, but you can still take close-up shots because of that long focal length. The trade-off is that further you are from your subject, the more prone your photos will be to camera shake. That's why I prefer lenses with short minimum focal distances and moving right up close to the subject (often denoted by the Macro label). In that sense, the 1.5ft minimum focal distance on my 50mm Sigma is its most disappointing attribute.

Outside of these printed specs, you'll also want to consider factors like the speed of the autofocus motor. The speed on the Canon 17-40mm is super fast compared to that on the 50mm prime, which is something you can't fully comprehend from a specs page. This is yet another area where different lens makers each have their own proprietary technologies and names for them--USM for Canon, AF-S for Nikon, SSM for Sony, and HSM for Sigma.

Another consideration is the number of aperture blades when shooting with a wide aperture lens. Canon's 50mm 1.4 has a diaphragm made of eight blades, but Sigma's 50mm 1.4 has one more blade--and they're curved. That means you theoretically get smoother bokeh circles in out-of-focus areas. It's these little things that account for the many hundreds of dollars in price difference between two otherwise seemingly similar lenses.

There are many other nuanced attributes to a lens that you can't get just from reading its specs--weight, micro focusing capability, lens elements, weather sealing, distortion, etc. That's why renting and actually using a lens for at least a week before you commit to buying one is recommended if at all possible. I'm still learning here too, and would love to know what else I'm missing. What are the things you look for when shopping for a new lens and testing one out?

And now, on to this past week's photo challenge. I asked members of our Tested Flickr Group (which just hit 100 members!) to take a photo of any piece of sporting equipment, and the entries you submitted ranged from tennis rackets to bowling balls. Sporting equipment has really great texture, and the photos submitted showed off that diverse patina really well. My favorite came in early in the week from user Dezerd, who took this photo of an old baseball in natural light. I like the shadows case over the aged ball and faded purple marking just out of focus--an indication of a history we can only imagine. It was pretty much exactly what I had in mind when thinking of the challenge.

Photo credit: Flickr user dezerd from the Tested Flickr Group

My own photo of a baseball shows my current infatuation with composition and Adobe Lightroom. Like with last week's photo of a coffee mug, I'm still drawn to table corners and the use of Sinister and Reciprocal diagonal lines in an image to draw your focus. Don't worry about those terms for now--I'm still reading up on them too and will write about them in the future. In Lightroom, though, I'm falling into a trap of jacking up contrast and vibrance in RAW photos, almost to create an Instagram-filter quality. The experimentation is really fun, but still a work in progress. My goal in this photo was to emphasize the red stitching, which is why it's in the light while the autograph (from San Francisco Giants Manager Bruce Bochy) is in the shadows. I'm also pleased about the way the stitching in the background gently curves around the silhouette of the ball.

For this week's challenge, how about something more accessible: take a photo of your gaming mouse or mice collection. No excuses this time--I know you have at least one! See you next week!