What the Numbers on Your Lens Mean?

If you’re new to DSLR or interchangeable lens systems, here’s a quick brush up on what all those numbers on the side of the lens mean.

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FOCAL LENGTH

If you have a zoom lens you will have a ring that turns to zoom in and out and it will also indicate what focal length you are currently set to. For example of your lens is a 70-200mm like mine you may see this which indicates I’m at 100mm currently.

MAXIMUM APERTURE

The maximum aperture is the largest opening (the smallest number) on the aperture scale that your lens is capable of opening to.  Larger apertures like f2.8 or even f1.8 are highly desirable because they let in more light and allow you to shoot in low light conditions without getting camera shake.  (for more on that read 5 Tips for getting sharper images or Why the 50mm lens is your new best friend) This will vary from lens to lens and you may actually see a range of numbers such as 3.5-6.3.

You can usually find this information in one of two places on your lens, or perhaps even in both places:

  1. right on the end of the lens barrel on the edge
  2. on the front of the lens inside the filter ring area.

In the example below you can see two different lenses.  My Tamron 17-35mm (notice the focal length range is shown there also) and my 85mm. On the Tamron you see “1:2.8-4? and on the 85mm you see “1:1.8?.   What that means is that the maximum aperture on the 85mm lens is f1.8, but on the Tamron zoom it changes from f2.8 to f4 as you zoom the lens.  At the lenses widest, 17mm, I can open the aperture to f2.8, but if I zoom all the way in to 35mm now my maximum aperture is only f4. This is pretty common with kit lenses and ones that have a large focal length range such as 28-300mm or 18-200mm.

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