[ATM] cassegrain perforation size

[lance clarke <alaskawolfjoe@hotmail.com>]

Hi,
I'm finished hogging, and need to determine the size of my Dall-kirkham perforation.
The primary is 150mm f/4, the secondary is 45mm and the effective focal length of the entire system is f/16.
 
This is intended to be a "grab and go" scope for use in the city.
 
I figure that about 40mm is good for the hole, but this is just kind of a hunch based on the secondary size.  Should I be considering the focuser in these decisions?  I figure a 2" would be overkill, so I've been leaning to an 1-1/4 focuser, to keep things light.
Any suggestions would be very much appreciated.
 
Lance
Toronto
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