Fraunhofer Diffraction - A Primer
Posted 03 September 2009 - 09:12 PM
Are the angles of the "Y" 150°, 60°, and 150°?
Posted 17 September 2009 - 02:32 PM
Very nice article btw.
Posted 26 January 2013 - 07:02 PM
Edit: Has anyone else tried making one of these and comparing them to a Bahtinov (or other) focusing mask? I'd like to have some more data points.
Posted 10 February 2013 - 11:49 PM
I don't want to get too picky with you guys but I need to make a correction here: the distinction does indeed matter. The entrance pupil is the image of the stop in object space. For a Newtonian (or simple refractor,) the stop is at the objective (the primary mirror surface or the lens) and the entrance pupil lies in the same location--not at infinity. Remember, the chief ray (which defines the maximum field angle) passes through the center of the stop and the pupils (both entrance and exit pupils). Telecentric systems have the stop imaged at infinity so that the chief ray is parallel to the optical axis. Simple telescopes are not telecentric. The exit pupil, on the other hand, is the image of the stop in image space. If you forget about an eyepiece and consider the intensity distribution in the focal plane, these calculations simply look at the effect on PSF for binary apodization of the exit pupil--assuming no wavefront errors.
One other thing to understand about these type of FFT calculation is that the results are only an approximation of what you will actually realize in an optical system. The results are close but there are aliasing and leakage effects (energy leaks from one Fourier period into surrounding periods) that cause small errors. If you know what to look for, you can see a lot of this stuff in these results (mainly because of the low sampling rate.) In order to show what these patterns will do as you add a lot of defocus, you need to use a near-field, Fresnel model. Far field computations can accurately model only a few waves (<5-10 ?) of defocus.
Posted 04 March 2013 - 04:42 PM