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What is a “Kit” Lens?

March 20, 2012

When you buy a DSLR, it often comes with something called a “kit lens.”  It’s an entry-level zoom lens that has a variable aperture. For example, my Canon T1i came with a 18-55 f/3.5-5.6.  The kit lens is a totally fine lens, but it does have some limitations. The “variable aperture” means that as you zoom in and out, the maximum aperture changes.

So, say you are in aperture priority mode (Av/A) for example, and you have decided that you want a blurry background. Because you want a blurry background, you’ve chosen a wide aperture (small f/number) like f/3.5. Well, if you zoom in the lens because you want to frame your subject differently, or because you want your subject to be bigger in the frame, your aperture on a variable aperture lens changes! Even though you dialed in f/3.5, as you zoom it changes! If you zoomed all the way into 55mm (as far as that kit lens zooms) your maximum aperture would now be f/5.6 instead of f/3.5.

Why is that an issue? Well, as your aperture gets smaller (bigger f/number) the amount of light entering your camera gets less. To compensate, the camera is going to choose a slower shutter speed. Sometimes it’s too slow of a shutter speed, and you’ll get blur as a result. (This is especially true inside, where the light isn’t as plentiful).

Additionally, if you are shooting in manual mode zooming in and out with the kit lens (or any variable aperture lens) you will have to continually adjust your settings to account for the fact that your aperture is changing.

How can you avoid that? You can dial in an aperture of f/5.6 (which is the widest the lens opens when zoomed all the way in). Now when you zoom in and out the aperture won’t change, it’ll just stay at 5.6.

The beauty of DSLR cameras is that the lenses detach, so you can use different lenses for different purposes.  For a beginner, the kit lens can be an affordable way to have a zoom lens!  Over time, if you decide that you want more flexibility out of your camera, you can upgrade to a higher quality lens!

Posted by Sonja and Shari (MWAC hosts)

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