Obs Astro OPTICS Part 4

1. when light rays from perpendicular cross sections of the image cone do not have the same focal distance along the optical axis. It is therefore an error both of focus and of magnification. (11)
5. a failure of focus, caused when rays parallel to the optical axis have different focal lengths at different aperture heights s. It produces a roughly uniform, concentric defocus around all the bright elements in all parts of an image, and a blurring in ex (9, 10)
6. the process of adjustment that eliminates tilt and decenter from the optical system (11)

2. is caused by a failure to magnify the image equally as the field height increases. It is characterized in two ways. In positive or rectilinear distortion and In negative or angular magnification distortion (10)
3. the longitudinal displacement of the effective focal plane from the first order or Gaussian focal point. This causes a radial expansion of the image point on the effective image plane, decreasing the luminance of each point and causing point images to ove (7)
4. a failure to magnify equally off axis light rays passing through the objective or eyepiece. Unlike spherical aberration, the effect is not constant within the same concentric aperture height height (s); instead the magnification also varies with field hei (4)
7. the rotation of an optical element around an axis that passes through the center of the element and is perpendicular to the optical axis (4)
8. the displacement of an optical element so that its center is no longer on the optical axis (8)

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