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CAMERA LENSES 16.25

the same D. In other words, for the same image-quality level and format size, wide-angle lenses have lower AD values than do narrow angle lenses.

16.5 LENS PERFORMANCE DATA

A wide variety of camera lenses has been selected to show typical performance characteristics. In most cases, the data have been derived from the referenced published United States patents. The authors have taken the liberty of reoptimizing most of the data to arrive at what would, in our judgment, correspond to production-level designs. All performance data have been shown at maximum aperture. It is important to realize that photographic lenses are invariably designed so that optimum performance is achieved at F-numbers at least 2 stops slower than maximum. A general explanation of the data page follows.

The lens drawing shows the marginal axial rays together with the upper and lower meridional rays for seven-tenths and full field.

The lens prescription and all other data are in millimeters. Glass catalogs are Hoya, Ohara, and Schott. Distances to the right of a surface are positive. A positive radius means that the center of curvature is to the right of the surface. The thickness and glass data indicate the distance and medium immediately following the particular surface.

The optical transfer function (OTF) plots show the through-focus modulation transfer function (MTF) on the left and the OTF at best axial focus on the right. The data are shown for five field points, viz., the axis, 0.35H, 0.70H, 0.85H, and 1.OH, where H is the maximum field angle in object space. The actual field angles are indicated in the upper-right-hand corner of each best-focus OTF block and are in degrees. The throughfocus data are at the indicated spatial frequency in cycles per millimeter with an additional frequency on-axis (dotted curve). Both the through-focus and best-focus data indicate meridional (solid curves) and sagittal (dashed curves) MTF. The modulus scale is on the left of each block and runs from zero to one. The phase of the OTF is shown as a dotted curve in the best-focus plots. The scale for the phase is indicated on the right of each best-focus block and is in radian measure. All the OTF data are polychromatic. The relative weights and wavelengths used appear in the lower-right-hand corner of each page. The wavelengths are in micrometers and the weights sum to one. The axial focus shift indicated beneath the best-focus plots is relative to the zero position of the through-focus plots. The best-focus plane is at the peak of the additional axial through-focus plot (dotted curve).

Vignetting for each field angle is illustrated by the relative pupil area plots on the right-hand side of each page. The distortion plots shows the percentage of radial distortion as a function of fractional field height. The MTF Astigmatism plot shows the loci of the through-focus MTF peaks as a function of fractional field height. The data can be readily determined directly from the through-focus MTF plots.

Certain acronyms are used in the System First-Order Properties:

Effective focal length (EFL)
Back focal length (BFL)
Front vertex distance (FVD)
Barrel length (BRL)
Entrance pupil distance (ENP)
Exit pupil distance (EXP)

The ENP and EXP data are measured from the front and rear vertices of the lens,