Quote:
Originally Posted by ptc
The airy diameter is determined solely by the f# and the wavelength of the light
Ray, you are confusing imaging of an Airy disk with the properties of the disk itself
if you want to image the disk you need to follow normal Nyquist sampling criteria
this is a very important zeroth-order issue.
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We can equally accurately say that the angular diameter of the Airy disk is determined solely by the aperture and the wavelength of light.
You are looking at linear measures in the focal plane and I am looking at angular measures in the field.
Since we are talking about the appearance of stars in our images, I think that it is necessary to incorporate the image sampling process as well as the Airy pattern generation in the analysis. The "20 micron pixel" comment shows why that is important.
I chose to use the angular frame of reference because:
- It is universally used for specifying optical parameters - resolution, field of view, seeing, sampling etc are all angular terms. The standard Airy disk formulation is an angular one.
- I wanted to incorporate seeing (which completely changes the PSFs) and the convolution applies in the angular domain, not on the focal plane.
- I wanted to avoid the odd outcomes that occur with a linear focal plane analysis, without consideration of sampling. For example, such an analysis would suggest that an f1.4 23mm Samyang lens will have smaller stars and better resolution than the 3.9m f3.3 AAO Telescope, because it has a lower FNo and smaller Airy disk. But we all know that the AAO will vastly outperform the small lens. An angular analysis shows that the angular resolution depends on the aperture and, along with sampling considerations, this explains why the performance of the big scope far exceeds that of the small lens.
Despite the differences in our approaches, I am sure that we agree that star size and shape in our images is determined solely by the physics of the image formation process (and I would add, the sampling) and that it is not due to charge diffusion in the detectors. That at least is a major step forward - thank you.
Regards Ray