[casstony]

Not sure if it's cool to pinch whole posts from other forums, but this info from Roland Christen is very informative:

There is a real difference between these two optical systems. Although both are SCTs, the Meade has an aplanic coma-free design, whereas the Celestron is an all-spherical mirror design similar in performance to a Dall-Kirkham along with characteristic off-axis coma.

What does this mean to you the average telescope user? Well, having a coma-free design puts other restraints on the optics. The corrector of the Meade ACF is twice as strong as the Celestron, resulting in more sphero-chromatism on axis. The result is lower performance on-axis but better off-axis images for the Meade. The Celestron all-spherical design theoretically would have better on-axis performance and worse off-axis.

Can you see the difference normally? Visually there is little benefit to the off-axis coma-correction of the Meade. Only when using it for CCD imaging with big chips would you see the benefit to the wider corrected field of the ACF. Stars are sharp over a wide CCD field, whereas the celestron shows quite comatic stars not too far off-axis. One can tame these somewhat with certain telecompressor accessories, but not fully supress them.

There are other considerations besides this if you are primarily a visual user. An 11" scope has more light grasp than a 10". Mechanically there are differences also. Mirror shift, collimation shift, focus shift as you move the scope around the sky can put a real damper on your observing pleasure (these are real problems and all these scopes have them to some degree - minor in some, major in others). The Celestron design certainly is fussy with collimation, but the ACF design with its hyperbolic secondary is many times more sensitive to miscollimation. You should check these scopes out before you buy.