Ah, I get it. I was referring to the theoretical resolution of an unobstructed aperture, wheras you and Erik were talking about the effects of diffraction caused by a secondary obstruction. But if you assume the 40-inch in the argument to be of the same optical configuration, with a similar sized secondary by percentage of aperture, we are back on an even playing field. And calling effectively a 41 inch aperture is misleading without specifically referring to resolution. I consider myself schooled on this point. Thanks, Brent. The Grim does have the same limitations of field of view, but because it is driven, that limitation isn't so bad. Large objects still cannot be seen in a single FOV. One of the penalties of long focal length, with generally comes with large aperture. On Tue, Oct 29, 2013 at 2:39 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary.