Have a look at this link:
http://www.nfilipovic.com/astrophoto...00k-ota-review
The graph shows 5 different optical systems.
The 5th row down of the optical results is for:
Quote:
5) Shape of the spot 10mm off-axis, in the plane shifted to compensate for field curvature.
Field curvature is defined according to the minimal RMS spot radius.
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You can clearly see that the spot size for a Newt. is much greater than an RC.
(The SCT is shocking.)
I wish I could find a higher resolution image of this graph of optical results.