Don, with the exception of anti-reflection coatings, all telescope optics (mirrors, lenses, eyepieces, barlows, field flatteners, coma correctors etc) are designed to operate in the regime of geometric or ray optics and are based entirely on ray optics principles. Here, wave phenomena such as interference and diffraction can be completely neglected and light can be viewed as consisting of localised rays rather than extended waves that fill all space. Or, equivalently to the ray picture, you can think of light as point particles bouncing off mirrors and bending at air-glass interfaces according to the law of refraction. Ray optics does not contradict wave theory, but it is a special case of it, i.e., the short wavelength limit.
The ray optics approximation is completely valid for telescope optics in normal use, and only starts to break down at the diffraction limit of the scope, i.e., when one uses enough magnification to start seeing diffraction effects (e.g., Airy disk star images). (It does fail to predict some subtleties e.g. diffraction spikes from spider of a Newt but these are irrelevant in the present context.) It is perfectly valid to split the mirror into multiple components (e.g. a slow part and a fast part) and then figure the total light intensity in the focal plane to be the sum of the light intensities from its composite parts. And the statement that a given f-ratio mirror also contains all slower f-ratios is correct also.
Coma is a geometric property of the parabolic mirror. It is entirely a ray optics phenomenon and is corrected by optical devices such as the paracorr within that theoretical framework.
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The point to get across, here, is that the linear size of a comatic image will be exactly the same size 15mm off axis in any scope of the same f/ratio
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FOR IDENTICAL FIELDS OF VIEW, THE LINEAR SIZE OF COMA WILL BE IDENTICAL FOR ALL FOCAL LENGTHS OF A PARTICULAR F/RATIO.
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Yes, this has been stated a number of times, and I believe everyone who posted about it in this thread agrees on this point.