Effects of obstruction on the figure of diffraction
This would be the case for example in solar observation when we use a sub-aperture visual filter, or an offset sub-aperture ERF fiter, or an offset Fabry-Perot etalon.
The top row presents the geometry of the various diaphragms, and the bottom row the associated diffraction figures.
From left to right, we have :
- a diaphragm with an open hole of 0.33 D : the resolution is set by the diameter of the open hole,
- a diaphragm with two symetrical open holes of diameter 0.33 D : the resolution is still set by the diameter of the open hole.
- a diaphragm with four symetrical open holes of diameter 0.33 D : the resolution is improved, but still lower than than the resolution provided by the full aperture.
- a full aperture with a diameter of D and a central obstruction of 0.33 D (typical of Schmidt-Cassegrain telescopes).
The previous images were calculated with Iris software using the formula : PSF = [ Module FFT (Aperture) ]^2
They are displayed in log visualisation.