4. Small f/number, “fast” system, little depth of focus, tight tolerances on placement of components Large f/number, “slow” system, easier tolerances, nearly parallel rays through filter F/number = focal length ÷ aperture Also, reciprocal of “relative aperture”

5. Same primary mirror, but very different f/numbers

6. Primary is f/2.63, but system is f/31.2 !!

7. Spherical aberration—focal length depends on radius where ray strikes mirror/lens.

8. Note circle of least confusion, the “best” focus Image of a point source is usually a bright dot surrounded by a halo of light Effect on extended image is to soften the contrast and blur the details

9. Chromatic aberration

14. The primary “monochromatic” aberrations are: Spherical aberration Comatic aberration (“coma”) Astigmatism Petzval field curvature Distortion

15. Coma Affected by where the light rays hit the lens/mirror Same focal plane, but different magnification Coma varies with the shape of the lens, and the position of any apertures/stops. Size of coma patch varies linearly with its distance from the axis

17. Astigmatism Image of a point source is not a point, but takes the form of two separate lines Between the astigmatic foci, the image is an elliptical or circular blur Circle of least confusion increases in diameter as the object moves further off-axis Image loses definition around its edges

18. Field curvature

19. Schmidt camera

20. Distortion

21. Example: If we increase aperture diameter by 50%, and reduce field of view by 50%, then ‘y’ is 1.5x the original, ‘h’ is 0.5x the original Coma increases by 1.125 Curvature reduced to 0.25 of previous amount Blurs due to astigmatism or curvature will of 0.375 of original size y = distance of image from optical axis h = distance of object from optical axis