When I purchased my first f/4.5 Newtonian in February 1992, I learned about the need or reason for offsetting the diagonal. This was something totally new to me, as all my previous reflectors had focal ratios of f/8 or slower.

From my instruction book for the 10-inch Meade f/4.5 Newtonian which was beneficial for me at that time. I’m including a couple pages as following:

Meade Instruments Corp.

Newtonian Notes: Possibly or “arguably” one of the best books covering everything and anything someone would want to know about how to collimate a Newtonian reflector.

A page from “Newtonian Notes” as following, concerning the purpose and need for offsetting a diagonal.”

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