Herschelian Relflecter?

Hello All!
Earlier this month I posted a question about the possiblity of a flat primary. One Astron-Marter told me the focal point would be infinity, another told me to try to find the deminsions of the porter hill telescope.
Today, I came accross a design by Willaim Herschel. This, I think, uses a flat primary to direct the light straight into the eyepeiece. Is building this kind of scope difficult?
-Adam

The Herschelian does not use a flat mirror - a flat mirror will not form an image. The Herschelian is simply a Newtonian design without a secondary, so the primary is tilted so that the image can be examined with an eyepiece without getting the observer's head into the path of incoming light. Since the primary is working off axis, the images suffer from coma and astigmatism. You can minimize this by using a very long focal length primary. Modern versions may use primary mirrors that are off axis sections of a parabaloid, or may use some type of corrector to control the aberrations.