The Crop Factor: One Extra Tip Before You Buy a Lens

by melissa

Here's a photography side note for the day, one I hinted at in my lenses post.

Maybe you've been eying the 50mm lens, because you heard it's the "must have" lens, the closest to being what the natural eye sees, the versatile, do-it-all, can't-go-wrong, nifty fifty. Maybe I'm the one saying all those things :) But before you go jumping on the 50mm train (the very one I suggested in my last post), you might want to know that chances are incredibly high that there's a different lens that you should be getting instead of the 50mm. One that will better do the job for your camera.

Here's why.

(And don't worry, you'll definitely know that lens to get by the end of the post :)

Most digital cameras have cropped sensors instead of full-frame sensors. Having a cropped sensor means that the photo your camera will take with any given lens will be a cropped version of the photo a full-frame sensor camera would take with that same lens. Think of it as being zoomed in. That means any lens you put on your cropped-sensor camera is acting as a cropped version of its actual focal length (mm number), meaning it won't fit as much in the photo as it does at its full capacity on a full-frame sensor. I think this is most important for a fixed/prime lens, since you don't have the option to zoom in and out with the camera to make up for the loss in the crop.

So about that beloved prime 50mm lens...putting a 50mm on a cropped sensor is like putting a mat board over the outer edge of your photo and cutting it off. Which means a 50mm lens on your camera would not be acting like a 50mm lens. It would be acting more like an 85mm—or like a 50mm with a magnifying glass over it.

You can see above how each crop factor (1.3x, 1.5x, or 1.6x) crops in a significant amount from the full-frame photo. This would be the difference between the exact same photo taken at the exact same spot with the exact same lens, but with four different camera sensors.

In other words, you have to have a full-frame sensor to get the true size out of your lens. That said, you don't have to have a full-frame sensor to get awesome photos. The crop doesn’t alter image quality, because you can still take amazing photos with cropped sensors, and they are actually more common than full-frame sensors. But for taking portraits of people, especially when you don't have the space (or time—those kids are lightning fast!) to back away from your subject to get everything you want in your shot, the crop can make quite a difference in what you're fitting in your frame. The key here is to be aware of the crop, and then buy your lenses accordingly.

What crop factor does your DSLR have? (last I checked...)

• 1.3x: Canon EOS 1D, 1D Mk11
• 1.5x: Nikon D40, D50, D70s, D80, D90, D200, D3000, D5000, D2XD2Hs Minolta 7D, Fuji S3 Pro Pentax, K100D, K110D, K10D
• 1.6x: Canon EOS Rebels, 7D, 20D, 30D, 40D, 300D, 400D
• 2.0x: Olympus E-400, E-500, E-300, E-1

Knowing that you have a cropped sensor can allow you to compensate for the crop when you go to buy a lens, and we've created a lens conversions chart to help you do just that. So if you've read rave reviews about a certain lens that you've now got your eye on, make sure the reviews are particular to your camera's sensor size—and if they're not, check out our chart below to see which lens you should buy to get the right crop that you are expecting from your next lens. My guess is that you're going to walk away wanting a 35mm. What do you think?

Challenge of the week:
Find out if your camera has a cropped sensor. You can do this. Figure out your model. Then google it. Or check your manual. If you have a cropped sensor, now you know, and you're one step ahead the next time you're on the market for a new lens. Then you can start researching a new lens focal length that better suits your sensor (or just use the chart above).