We start off by examining the two highest resolution images of Mars ever taken from anywhere near Earth, by the Hubble Space Telescope (HST) when Mars was at its closest in 60,000 years. Have you clicked on "original" size below? The scheme used here sort of uses reverse Nyquist. The aim is to use 2 pixels on your monitor to equal the Full Width at Half Max (FWHM) of the diffraction disc of the telescope used. The FWHM of a scope with an aperture diameter A can be written as:

FWHM = 1.02 * wavelength / A

Sorting out the units and using the wavelength (555nm) at which the eye is most sensitive, we end up with:

FWHM (in arc-seconds) = 4.56 / A (in inches)

E.g. 0.33arc-sec for a C14, 0.57arc-sec for a C8, 1.14arc-sec for a 4" APO, etc. When we use Nyquist "sampling" (Nyquist "display" in the current exercise, 2-monitor-pixels = FWHM) we expect that essentially all detail that is available in an image should be visible. Basically, if we enlarge the image beyond that, we are employing empty magnification, introducing unnecessary bloat. Trying to sharpen up the larger image does increase acutance, but at the expense of introducing artifacts. In any case we cannot invent detail finer than already contained within the diffraction limits of the scope. It's easy to verify that no matter how fancy we get with our sharpening algorithms, it's very unlikely that we can significantly improve the legibility of the writing in the large, bloated images above.

The HST images in the top row are displayed at Nyquist (2-monitor-pixels per FWHM) for a 20" aperture scope. The subsequent rows present the images as they would have been imaged by a perfect scope of smaller aperture under perfect seeing. Taking the smaller images on the right and resizing them larger to match the Nyquist-display of a 20" aperture scope gives a good demo of image bloat, on the left. The recipe goes as follows:

Obtain a JPL-NASA simulation of your planet for the date and time your image was taken, from http://space.jpl.nasa.gov/ This immediately gives you the planet diameter in arc-seconds. Divide that by the FWHM value for your OTA from the previous formula, multiply by 2 and you have the desired Nyquist planet diameter in pixels. Resize your image to yield that diameter in pixels. Do the same for the JPL-NASA simulation. Comparison of the two immediately gives you an excellent assessment as to how much of a shortfall you have between what is achievable with your aperture scope under perfect seeing, perfect optics, perfect technique and what you actually have.

Interestingly, the JPL-NASA simulations should not be taken as religious truths, but they do give a pretty good idea of the general level of detail that one should be striving for. Compare the HST images in the top row to the simulations, and note the not insignificant divergences. The following slides present my own humble images using a C8 and a C14.