9/22/16 Op)cal Equipment Ray diagram for magnifying glass 1 9/22/16 Define the terms far point and near point for the unaided eye. For the normal eye, the far point may be assumed to be at infinity and the near point is conven)onally taken as being a point 25 cm from the eye. Hyperlink Define angular magnifica1on. θ0 θi 2 9/22/16 The simple magnifying glass Derive an expression for the angular magnifica)on of a simple magnifying glass for an image formed at the near point and at infinity. Angular magnifica)on is = Object at nearpoint Image at nearpoint, object at unknown distance (u) Applying the lens formula with v = -­‐ve But angular magnifica)on is = 25/o At infinity 25/25 goes to 25/∞ Spherical Aberra)on Spherical aberra3on occurs because rays that enter the lens far from the principal axis have a slightly different focal length from rays entering near the axis. (also found in mirrors) May be reduced by using a smaller aperture (smaller lens), but that limits the amount of light passing through 3 9/22/16 Chroma)c Aberra)on Chroma)c aberra)on arises because the lens has different refrac)ve indices for different wavelengths. Thus, there is a separate focal length for each wavelength (color) of light. May be reduced by combining converging lens with a diverging lens, of a different refrac)ve index, or by using monochroma)c light. The compound microscope and astronomical telescope 4 9/22/16 Construct a ray diagram for a compound microscope with final image formed close to the near point of the eye (normal adjustment). Students should be familiar with the terms objec)ve lens and eyepiece lens. 1. Construct ray diagram for objec)ve lens with u between f and 2f 2.Image formed by objec)ve lens becomes object for the eyepiece lens Image formed by eyepiece lens Image distance at near point of the eye 3. Construct ray diagram for eye piece lens with object between lens and f (but close to f). Construct a ray diagram for an astronomical telescope with the final image at infinity (normal adjustment). 1. Construct an off axis ray diagram for the objec)ve lens wit the object at infinity Rays are parallel 2. Image formed by the objec)ve becomes the object for the eyepiece lens Rays are parallel 3. Make the distance between the eyepiece lens and the object = f for the eyepiece lens 5 9/22/16 State the equa)on rela)ng angular magnifica)on to the focal lengths of the lenses in an astronomical telescope in normal adjustment. Astronomical Reflec)ng Telescope 6 9/22/16 Astronomical Reflec)ng Telescope With a mirror, there is no chroma)c aberra)on. The mirror is supported in the back, so it may be larger than a lens supported at the end Simple to use and cheaper than refrac)ng telescopes of the same strength. Single Dish Radio Telescope 7 9/22/16 Single Dish Radio Telescope Used to collect radio waves from space Can also be used to transmit radio waves into space to reflect off of other surfaces Connected to equipment for measurement Radio interferometry telescopes 8 9/22/16 Satellite-­‐borne telescopes Even the best telescopes on Earth s)ll need to contend with the atmospheric interference. Gebng out of the atmosphere removes the twinkling of the stars, and allows for a clear image of the star 9