DX, full-frame, APS-C, FX, crop factor, 24×36, image circle. Confused yet? Good.

With the new Nikon D700 hitting store shelves and the Canon 5D MkII imminent, now is a good time to clear the air on the whole sensor size thing.

Back in the film days, the rectangle that captured the image on a standard SLR (the film) was one size: 24mm x 36mm. That was all there was to it, and nobody really gave it a second thought.

Every camera manufacturer is slightly different; models from the same manufacturer are even different. People usually refer to a sensor’s size by its “crop factor.” That’s the number you use to find the 35mm equivalent of a given lens. It’s just like taking the middle of an image and throwing away the outside edges. If a sensor is 24mm x 36mm, then there is no crop factor, since it covers the same area as 35mm film.

Nikon has two different sensor sizes: full frame (FX) and 1.5x (DX).

Canon has three sensor sizes: full frame, 1.3x and 1.6x. Other manufacturers are in the same range, with Olympus being the notable exception, at 2x.

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Some people don’t like the term “full frame” because it isn’t specific. Full compared to what? For the sake of simplicity, when I say “full frame” I mean a sensor that’s roughly 24mm x 36mm.

That’s all well and good, but why should you care? Sensor size is important when you’re trying to pick a camera because full frame sensors have distinct advantages and disadvantages in different situations.

In general, full frame sensors have better image quality across the board, but they really shine when it comes to high ISO performance.

Take a look at the Nikon D300 and it’s full frame sibling the D700. The D300 is widely considered to be pretty good in low light, but the D700 is much better. In the real world, my D700 gives me 2 full stops of useable ISO over the D300; I can shoot at ISO6400 on the D700 where I wouldn’t shoot above ISO1600 on the D300. This has a lot to do with the size of the sensor. Both cameras have 12 megapixels, but the individual imaging sites on the D700 are farther apart, giving you a cleaner image.

Full frame sensors also give photographers more options when it comes to wide-angle work. I can use my $300 24mm f/2.8 instead of the $900 Nikkor 12-24 f/4, and the 24 is faster.

The downside is that full frame sensors and lenses are bigger than their cropped counterparts. Full frame bodies are also more expensive.

There are also some situations where the crop factor helps you. Many people have gotten used to having a little big of extra reach with their long lenses and may not want to give that up.

Crop Sensor vs Full Frame Sensor: Choosing Which is Right For You

After you figure out the difference between a crop sensor and a full frame sensor, you’ll need to decide which one suits your needs.

For the average consumer, a smaller 1.5x or 1.6x sensor will be fine. If you’re the kind of person who has the 18-55 kit lens and maybe one other lens, it just doesn’t make sense to spend the extra money on full-frame.

If you have lots of glass from the film days, it might be worth looking into a full frame body. Modern Nikon bodies are compatible with nearly every lens Nikon ever made, and Canon bodies all work with EF glass.

Photographers who enjoy shooting landscapes and architecture will definitely want to check out a full frame body (if they don’t already have one). Full frame image quality and wide-angle options are far better than their cropped siblings.

If you shoot in natural and available light, you’ll definitely want to check out a full frame body too. The high ISO performance on my D700 is simply unmatched by any body with a smaller sensor. I can shoot at ISO6400 without worrying about excessive image noise, and I have more options when it comes to using (or not using) strobes and artificial light.

For nature, wildlife and sports enthusiasts, it might make more sense to stick with a smaller sensor. You can take advantage of the crop factor to get maximum detail at long distances.

Jamie De Pould is a DPS critique moderator and freelance photographer. He is currently pursuing a M.S. in Photography at Syracuse University in Syracuse, NY. See some of his work at pbase.com/jdepould.

Read more on this topic in our previous article – Crop Factor Explained where we specifically look at the topic of Crop Factor and how it impacts the different lenses that you might use on your DSLR.

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