The skywatcher maks are faithful to the original design in that the aperture stop is at the corrector - not the primary mirror, and yes the primary mirror diameter is larger than the clear aperture.
There is a simple “flashlight test” you can do in a long hallway or garage - measure the clear aperture of the corrector with a tape measure. Put a bright LED at the focus and adjust carefully so that the scope illuminates a spot on a distant wall of the same diameter. Now walk back to the scope and measure the width of the beam coming out of the corrector. This is the effective aperture of the scope.
An alternative view is that they started with the largest primary mirror that will fit inside the OTA, and the corrector aperture is thus slightly reduced in respect to that.
There is a reason why this is important, optically; too complicated to go into here. The maks from Intes and Questar likewise.
With the mak-newtonians the field of view is larger than it is in the mak Cassegrains so the ratio between primary and corrector varies accordingly.
If you want the full theory obtain a copy of sky & telescope “Gleanings Bulletin C”, it spells out everything you may want to know about maks.
Last edited by Wavytone; 27-10-2018 at 06:38 PM.
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