Interpreting the Results
Whatever the results show for your lenses, the important thing to bear in mind is that this is just information, and it's up to you how to use it. Don't be put off from using the widest and narrowest aperture settings just because you know the image quality will be better at f8 or f11. Creative reasons often supersede technical ones—you may need to stop down to f16 or f22 to get an entire scene in focus, or you may want to use the widest aperture on your lens for narrow depth-of-field. Don't forget that if your subject is static you can always "bracket"—for example, you can take landscape photos at f11, f16, and f22, deciding afterward which image is the best.
When I first bought my 85 mm f1.8 lens, I took a lot of photos with the aperture set to f1.8 because I liked the narrow depth-of-field. But I soon realized that I often got better results at f2.8, as the image is sharper, and the extra depth-of-field helps compensate for any focusing errors (see Figure 12). This is an example of how I put the results from lens testing into practice.
Figure 12 This is an enlargement of the portrait shown earlier in this article. A close examination of the model's eyes shows that I focused on her eyelashes, not on her pupil. It's a good demonstration of how narrow depth-of-field is at f2 with an 85 mm lens on a full-frame camera. Now I tend to take portraits at f2.8 with this lens—not only is the image quality better, but there's a little extra depth-of-field, which helps to compensate for any focusing errors.