While we can ruminate on pixel size and focal length, I have found for "diffraction limited" optics...and Lord knows that is not a given
that so many other aspect conspire to smudge your images, far more than an imperfect optic.
eg:
Environmental factors (seeing, local environmental temperature, transparency )
Mechanical factors: Tracking accuracy, guiding accuracy, wind buffeting and vibration suppression, OTA rigidity, collimation retention, focuser rigidity.
Thermal control: Suppression of tube currents, optical figure retention, focus retention.
.....and apologies to Stefan for the digression..
Best Astrograph? Simple.
*Anything* made by Astro-Physics.
