On Monday, July 18, 2016 at 3:46:28 AM UTC-6, StarDust wrote:

What i read, reason for the larger CO is for photography. Before with the 19%
CO was more difficult to do photo, unless the camera/imager had a small CCD.

Interesting. Usually, a larger central obstruction is found in photographic
telescopes to better correct aberrations, and because contrast is not as
important for photography as for visual observing.

It certainly can be true that a small central obstruction could lead to
vignetting, particularly in prime focus photography, but this is the first time
I've heard of it being a consideration.

John Savard