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Shooting from One Location with a Single Lens/Focal Length

As you can see in Figure 1, and as discussed in Part 1 of this series, a full frame sensor (left) allows a specific lens at a specific focal length to capture a wider field of view than does the same lens at the same focal length on a camera using a smaller sensor (right).

Figure 1

Figure 1 All four shots were captured using the Canon EF 70-200 f/1.4L IS USM lens at 70mm.

Zooming in on comparable areas of the shots (see Figure 2), the images on the right, which were captured with the smaller sensor, appear to be marginally sharper. This sharpness is a result of the increased zoom factor.

Figure 2

Figure 2 Compare the zoomed images for sharpness.

Keep in mind that the zoom factor of a lens is multiplied by 1.6 when using the smaller sensor. So, in effect, the images on the left in Figure 1 were captured at 70mm, while the images on the right were captured at the equivalent of 112mm.

In Figure 3, the red box indicates the area captured with the APS-C sensor.

Figure 3

Figure 3 The same lens at the same zoom factor captures about 62.5% of the width and height on the smaller sensor, resulting in an image with pixel dimensions only about 40% as large as the full frame sensor’s photo.

So, how can you effectively compare the same lens at the same focal length on different cameras? Let’s take a look at what we might do with two of these shots.

Using comparable sections of the images, I prepared a pair of 8 x 10 inch images at 300 ppi. Looking at the same area in Figure 4, you can see that the image on the right, captured with the smaller sensor, is indeed somewhat sharper than the comparable area captured with the full frame sensor.

Figure 4

Figure 4 Capturing with the smaller sensor indeed produces a bit sharper detail, comparable to shooting with a longer lens or at a higher zoom factor.

So, does that mean the smaller sensor is actually better? Under one specific set of circumstances, yes, you might prefer the Canon 20D over the Canon 5D: If you are as close as you can get to your subject and if you are using your longest lens at maximum zoom, then the smaller sensor enables you to "zoom" closer and capture more detail. In sports photography, for example, the smaller sensor gets you "closer" to the action by increasing the lens zoom factor.

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