After posting the longest post ever to explain all the numbers and letters in lens names, I got loads of questions asking about those other little numbers on the end of your lens.
So take a look at this lens. The brand has been photoshopped out, but it’s a Canon EF-S 17-55mm f/2.8 IS USM. The 17-55 is the focal length. When it’s at it’s widest, it’s a 17mm lens. At it’s longest zoom, it is 55mm. And of course, it can be anything in between. The Φ77mm tells you the filter thread size for the end of the lens if you want to add a filter. The aperture is then listed as a ratio. On this lens, the max aperture no matter the focal length can be fixed at f/2.8 so it’s written as a ratio: 1:2.8. Some lenses might have a different max aperture depending on if you’re using it as it’s widest or longest and those would be two numbers like: “1:4-5.6″.
And this is a ‘nifty fifty’. Canon’s 50mm f/1.8. To the right, you’ll see a macro symbol and 0.45m/1.5ft is the minimum focusing distance achievable by the lens. So that tells you that if you want to use it to take a macro shot of a flower, for instance, you need to be no closer than .45m or 1.5ft from the object.