Labeling of Diffraction Patterns

Fig. D-1. Image notation: a) labels used on diffraction patterns, b) labels used on longitudinal slice patterns.

Figure D-1 a shows how the typical image pattern appearing in this book is labeled, and Fig. D-lb indicates the slight modifications to annotate slice patterns. In the upper left corner of any given pattern is a title, if one is present. In the upper right corner of a frame is a number that gives the reduced angular radius D6fk from the edge to the center of the square box.

In the case of the square diffraction pattern frame, this angle also applies to the horizontal axis. If the pattern had the number 1.22 here, the Airy disk of a focused perfect aperture would just be contained within the box (see Fig. D-2). Most of the focused patterns in the text have limits of 5 or 10, allowing us to inspect the ring structure as well as the central spot. Out-of-focus patterns are viewed at lower magnification, which accounts for the large numbers appearing in the upper right corners.

perfect 1.22

perfect 1.22

Fig. D-2. A. perfect Airy disk is barely contained within a box with a reduced angular dimension 1.22 from center to edge. The bright corners are the first diffraction ring.

The centered number at the bottom of one of the square patterns is the number of wavelengths of defocusing aberration. The numbers at the lower corners of a slice pattern denote the value of defocus at each end of the box, with the defocus changing steadily between them. Longitudinal slice frames are defocused an equal distance inside and outside focus, with the best focus near the center. In all slice frames, the objective lens or mirror is to the left.

In some cases, clutter is reduced by labeling only one frame in a row or column. If a defocus value is missing, the value appears at the bottom of the column. If the angular coordinate is missing on a particular frame, it can be found on a row entry on the far right.

For composite figures with a focused image frame appearing to straddle two lower columns, the inside focus behavior is the column to the left (negative defocus values), while the outside focus behavior (positive) is in the middle column. Such figures have the behavior of perfect optics in the column to the far right. These unaberrated columns give only one side of focus; the other side is identical. See Fig. B-3.

Fig. D-3. A focus-run pattern shows how the frames "fold over" the region of focus. The perfect pattern to the right need not show both inside- and outside-focus images because they are identical.