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Photography Tips: Understanding DSLR Lenses

Skill Level: Beginner

If you've ever shopped around for a lens, you know that the titles of lenses can get pretty lengthy and confusing. With all the different abbreviations, numbers and labels, the name of a lens can look more like a complex algebraic equation than a product title. So that's why I've decided to put together this blog post to help bring some clarity to the convoluted science of naming a lens.

Here are 2 examples of what a lens title might look like:

I mean really...it's a little ridiculous how complicated those titles are. I'm sure they make perfect sense to the marketing geniuses who came up with all these fancy titles, but to the average person, it's practically a bunch of meaningless letters and numbers. So let's break the names down and look at each part of it individually.

1. Lens Focal Length Range

Starting with the core of the lens title, we have the lens focal length range. The lens focal length is always measured in millimeters and it basically indicates how "zoomed in" the lens can go. Higher focal length numbers (e.g. 300mm) mean the lens will zoom in further, whereas lower focal length numbers (e.g. 20mm) mean the lens will have a wider view. For instance:

On the left: 28mm. On the right: 70mm (full-frame camera).

If the lens has a range of focal lengths, like 55-200mm, then the lens can zoom from 55mm all the way out to 200mm. Lenses that don't zoom are called "prime lenses" and they will be indicated with just a single focal length number - like the Canon 50mm f/1.4 USM.

2. Maximum Aperture

After the focal length range, the title will have an aperture number or a range of aperture numbers. This indicates the lens' maximum aperture. In other words, it tells you what the widest available aperture is for that lens. For instance, on the Canon 50mm f/1.4 USM, the widest aperture you can use is f/1.4 (remember that the smaller the f-number, the wider the aperture).

But then what's the smallest aperture you can use? Well, you'll have to dig a little deeper into the lens specifications to find that out. The minimum aperture for a lens (that is, the smallest opening) is never indicated in the title. Only the maximum aperture is. That's because the majority of customers don't care what the smallest aperture is. Most people want lenses that let in more light, not less. Only us landscape photographers care about the smallest aperture a lens can use.

Alright, now it gets a little tricky, so stay with me...

Some lenses have a range of apertures indicated after the focal length, like the Nikon AF VR 80-400mm f/4.5-5.6D ED lens. In this case the maximum aperture for the lens is listed as "f/4.5-5.6". When you have a range of apertures like this, that means the available maximum aperture will vary depending on how zoomed-in you are. The first aperture in the range indicates the maximum aperture for the short end of the zoom range. The second aperture in the range indicates the maximum aperture for the long end of the zoom range. This is called a "variable maximum aperture."

So in this example, the maximum aperture of the lens when you're set at 80mm will be f/4.5. But when you zoom the lens into 400mm, the maximum aperture decreases a bit to f/5.6. Having a variable maximum aperture like this allows the manufacturer to make the lens more compact and less expensive.

If your lens has a zoom range, but only 1 aperture listed, that means the lens' maximum aperture will be the same throughout the entire zoom range. For instance, on the Canon 70-200mm f/2.8L IS II, the lens can open all the way up to f/2.8, regardless of whether the lens is at 70mm or 200mm.

3. Features and Other Fancy Marketing Terms

All the other letters and abbreviations in the title of a lens will indicate features, quality and other marketing terms. For instance, if the maximum aperture has an "L" after it on a Canon lens - like the Canon 70-200mm f/2.8L IS II - then the lens is classified in its professional line of lenses. That means it'll most likely be weather sealed, the glass will be better quality, the image quality will be top-notch and the overall build will be more rugged.

There are a ton of different labels indicating all sorts of features and specs. Nikon especially has a very convoluted, over-complicated set of designations. Since there are so many, I won't bother defining all of them here, but I will address some of the most common ones. For a complete list of Nikon lens labels, check out this great article at DPanswers.com. For Canon's, here's a good article over at BobAtkins.com.

CANON

  • EF - "Electronic Focus" - This is the designation for all lenses fitting modern EOS bodies
  • EF-S - Same as "EF" except the lens is specifically designed for and will only fit APS-C format DSLRs like the 60D, 7D and Rebel series cameras (in other words, it won't fit full-frame cameras like the 5D or 1Dx)
  • USM - "Ultrasonic Motor" - This is what Canon calls their ultra-fast and ultra-quiet auto focus motor. USM lenses focus quickly, quietly and will typically have full-time manual override
  • IS - "Image Stabilization" - These lenses have built-in optical image stabilizer to help combat camera shake
  • L - This will come after the maximum aperture and it designates Canon's line of professional-grade lenses
  • DO - "Diffractive Optics" - This is a technology Canon uses in a few of its lenses that allows them to make telephoto lenses much more compact
  • Macro - A true macro lens will allow you to focus closer than a non-macro lens - good for photographing close-ups

NIKON

  • Nikkor - This is just Nikon's brand name for their DSLR lenses
  • AF - "Auto Focus" - If the lens has "AF" only (not "AF-S"), then the lens auto-focuses using the AF motor built-in to the camera. In other words, the lens itself has no AF motor. It relies on the camera body to drive the focus. Some Nikon cameras don't have a focus motor in the body, so they can't auto focus with these lenses.
  • AF-I - These lenses autofocus using an internal (that's what the "I" is for) AF motor built in to the lens instead of into the camera body as described above
  • AF-S  - The "S" indicates that it utilizes Nikon's current "Silent Wave" motor to auto focus. This type of AF motor is quieter and typically faster than the older AF-I motor
  • VR - "Vibration Reduction" - These lenses have built-in optical image stabilizer to help combat camera shake
  • D or G - It's kind of complicated. Check out this explanation at DPanswers.com
  • DX - This indicates that the lens is designed for and will only fit Nikon's DX "digital format" DSLR cameras
  • FX - This indicates that the lens will work on full-frame Nikon DSLRs as well as digital format DSLRs
  • ED - "Extra-Low Dispersion" - Indicates that the lens utilizes some special glass to help reduce chromatic aberration
  • IF - "Internal Focus"  - This means that the lens focuses by moving elements inside the lens barrel instead of moving the front element. As a result, the front of the lens won't extend out or rotate when focusing.
  • Micro - Nikon's indication for a macro lens