Quote:
Originally Posted by morls
In terms of observing, does this mean a larger central obstruction would make it easier to resolve stars in globular clusters? What would the effect be on observing faint galaxies, such as those in the Grus quartet?
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In the specific case where the separation of 2 stars are at or near the Rayleigh criterion (ie. radius of the Airy disk) then yes, a telescope with a central obstruction will actually resolve these stars better than an unobstructed one. However, at lower spatial frequencies (ie. greater angular separation for the double star) the unobstructed telescope will perform better. Yes, it is counter-intuitive but a by-product of the wave nature of light. In practice however, you would need excellent seeing to take advantage of this in order to split a double star that has an appropriate separation for your aperture.
For extended objects such as faint galaxies there will be a loss of contrast due to the fact that the image is comprised of many overlapping point sources, so the airy disks / rings get "smeared" all over each other. Since an unobstructed aperture has less energy distributed to the rings, this smearing is kept to a minimum and results in better contrast.