06_optics

Scope means f 2 70 mm 35 m scope means m 500 at f10

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: just an image of the entrance pupil satisfying 1/s’ + 1/(f1 + f2) = 1/f2 – size is smaller than entrance pupil by magnification factor • M = f1/f 2; in this picture, f1 = 48; f2 = 12; M = 4; s’ = 15 Winter 2008 Lecture 6 35 – dark adapted pupil up to 7 mm diameter (2–3 mm in daylight) – sets limit on minimum magnification (if you want to use the full aperture) • 210 mm aperture telescope must have M > 30 • for f/5 scope, means f2 < 35 mm; f /10 scope means f 2 < 70 mm • 3.5-m scope means M > 500; at f/10, f 2 < 7 0 mm Winter 2008 36 9 Geometrical Optics 01/31/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Vignetting Infrared Cold Stop • Rays that don’t make it through an optical system are don’ said to be vignetted (shadowed) – maybe a lens isn’t big enough – maybe your eye’s pupil isn’t big enough, or is improperly placed • An infrared detector is very sensitive to terrestrial heat • Often appears as a gradual darkening as a function of distance from the field center – the farther out you go, the bigger your lenses need to be – every optical system has a limited (unvignetted) field of view – beyond this, throughput goes down – so want to keep off of detector – if detector located at primary focal plane, it is inundated with emission from surroundings and telescope structure • note black lines intersecting primary focal plane • Putting a “ cold” stop at a pupil plane eliminates stray emission cold” – cool to LN2; image of primary objective onto cold stop – only light from the primary passes through; detector focal plane then limits field of view to interesting bit • Also the right place for filters, who prefer collimated light Winter 2008 37 Winter 2008 38 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Raytrace Simulations Aberrations: the real world • Lenses are thick, sin • In Google, type in: phet Google, – sin – tan – top link is one to University of Colorado physics education page – on this page, click: go to simulations – on the left-hand bar, go to: light and radiation – then click the geometric optics simulation link (picture) Lecture 6 7/5040 + … + 5/120 + 2 5/15 + 17 7/315 + … – spherical aberration • all spherical lenses possess; parabolic reflector does not – coma • off-axis ailment: even aspheric elements have this real and virtual images lens radius of curvature, diameter, and refractive index see principle rays (ones you’d use to raytrace) see marginal rays use a light source and screen see the effect of two sources Winter 2008 3/3 • Different types of aberration (imperfection) • Can play with lots of parameters – – – – – – 3 /6 + – chromatic aberration • in refractive systems only: refractive index is function of – astigmatism • if on axis, then lens asymmetry; but can arise off-axis in any system – field curvature/distortion • detectors are flat: want to eliminate significant field curvature 39 Winter 2008 40 10 Geometrical Optics 01/31/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Spherical Aberration • Rays at different heights focus at different points • Makes for a mushy focus, with a ha...
View Full Document

This note was uploaded on 01/30/2014 for the course PHYS 121 taught by Professor Staff during the Winter '08 term at UCSD.

Ask a homework question - tutors are online