A lens by any other name…

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During my classes one student inevitably asks “what lens should I buy?” I try to tell them the important differences between prime and zoom lenses. For any photographer who is looking to shoot sharper photos, prime lenses are the way to go. If you don’t know what a prime lens is then this blog is for you.

Prime lenses are distinct in that the lens barrel does not move or in photographic terms there is no zoom.  The focal length of the lens stays the same. To bring the subject closer, the photographer must walk closer. To make the subject farther away, the photographer must back up from the subject.

Zoom lenses on the other hand allow the photographer to stay in one spot and zoom in or out on the subject. These lenses are very popular standard lenses because they are light-weight and relatively versatile because photographers are not changing lens quite as often. Simply put, one lens can do the work of several. Thus, a photographer’s camera bag is lighter and easier to carry for long periods because he can carry fewer lenses.

The example above shows the lens specs for the Nikon AF Zoom 70-300. The maximum aperture size at a focal length of 70mm is f/4 but when the focal length is at 300, the maximum aperture size is now f/5.6. That is a loss of 1 f-stop. When compared to the prime lens, the maximum aperture does not change. It is always f/2.8.

The drawbacks to using a zoom lens is that they are not as “fast” as a prime lens. Lens specifications show that the maximum aperture for a typical zoom lens can loose as much as 2 f-stops of light from the shortest focal length to the longest on a telephoto zoom. This can be seen when you shoot in low light conditions and your photographs are blurry. In low light conditions the camera may be as wide open as possible (i.e. f/5.6) but because f/5.6 is smaller in size than f/2.8, the shutter speed needs to be longer. Long shutter speeds result in blur from moving subjects or camera shake when you are holding it in your hands to shoot.

Sadly, all DSLRs sold today come with zoom lenses. A better zoom option would be a zoom lens with a fixed focal length. These are higher in price because they are higher quality lenses. The two lenses below are great examples of the price difference between the two types of zooms. Note also the difference in size between the two.

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One reason I have stayed with Nikon for so long is that I can use my older prime lenses with my Nikon D300s. Not all Nikon digital bodies will accept the older lenses, but the investment in a body that does means that I can buy used lenses other photographers are getting rid of. The flower example above is an older Nikon AI manual focus lens compared to the newer zoom that came as the kit lens.

If you still have questions, do a lens comparison for yourself. The proof is in the pudding!

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