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Comparing Digital Camera Sensors, Part 1

1. Exploring Digital Camera Sensors
2. How Much of the Scene Does it Capture?
3. How Close Can I Get?
4. Summary
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How Much of the Scene Does it Capture?

So much for crunching numbers. What does the difference in sensor size mean when you’re actually capturing photos? You may hear or read that on a camera with a smaller sensor, a given lens will seem like a longer lens, or that such-and-such a lens has a ratio of 1:1.6, the "lens focal length conversion factor," on a camera with a smaller sensor. (The conversion factor compares to shooting with a 35mm camera using the same lens.)

The math is simple: If you shoot a 50 mm lens on a full-frame or 35 mm camera, you capture all the image the lens was designed to capture. If you stick that same lens on a camera with a smaller sensor (the APS-C size), the lens behaves more like an 80 mm lens on a full-frame or 35 mm camera. But how does that affect your actual shooting? What does it really mean in the field or in the studio? Let’s look at some test photos.

Shooting from the second floor of my studio, here’s the setup you see in Figure 3:

• The tripod is 25 feet from the fence, verified with the tape measure.
• The table to the right of the tripod holds the laptop (for checking the shots) and the lens case.
• The light blue line highlights a rope you’ll see in shots taken with the Canon 5D.
• The red line indicates the rope visible in shots taken with the 20D.
• Hugo the dog provides security and comic relief.

Mounting Canon’s exceptional EF 50 mm f/1.2L USM lens on the Canon 5D (full-frame) and shooting from 25 feet, Figure 4 shows how much of the scene was captured.

The 50 mm lens was transferred to the Canon 20D, which then captured what you see in Figure 5 from the same tripod and in the same location.

To capture the same smaller composition (field of view) using the same lens, the Canon 5D would shoot from about 15.6 feet rather than from 25 feet. The difference is illustrated by the relative positions of the tripods in Figure 6.

For the 20D to capture the same larger field of view as the 5D (Figure 6), the tripod would have had to be moved back from 25 feet to 40 feet.

In photojournalism, landscape photography, sports photography, and other such fields, how much of the scene is captured can be critical to the success or failure of a particular photo. Indeed, lens selection plays a huge role in successful photography, but there’s only one lens attached when it’s time to click the button. If that particular lens is zoomed fully in or out (or is a prime lens, a lens with only one focal length), the size of the sensor has a direct impact on how much of the scene is captured.

In Figure 7, you see a shot taken with the Canon 5D using the EF 24–70 mm f/2.8L USM lens at 70 mm. The red rectangle in Figure 8 indicates what part of that image would have been captured if the same lens at the same zoom factor had been on the Canon 20D at the time the photo was taken.

And that brings us to the next question: When composition, not field of view, is primary, what’s the difference between shooting with APS-C size sensor and a full-frame sensor?