Thanks for most of the replies. As the picture above shows, I understand that the image is manipulated by mirrors and lenses prior to viewing it from the ocular end. I doubt that there is a mirror or lens that functions to rotate the image 20 degrees clockwise for example. Most of my understanding of light waves involves the image either being reversed as in a mirror or flipped 180 . I was hoping that Mule Deer would offer an opinion as clearly he has an in depth understanding of the workings inside a rifle scope.
My guess is that viewing the reticle backward thru the objective is a more sensitive means of assessing wither the internals of the scope it self are square and plumb or not. I have noticed this to varying degrees with the rifle scopes I own, and the (few) spendy ones seem better.
Thank you.
