[ATM] Width of Dome Slit?

["N. Foldager" <nf@dadlnet.dk>]

I'm considering a dome to my observatory. To allow for future scopes 
I base the calculations on a  14" (35.6 cm) scope. 

The bottom of the cradle of my equatorial mount (AP 900GTO) is 21.5 
cm (8.5") from the node point of the mount (= center of dome). This 
means that the diameter of a 14" scope will reach out to 21.5 + 35.6 
= 57.1 cm (22.5") from the node.

Does that mean that the slit of the dome needs to be 2 x 57.1 cm = 
114.2 cm (45"); at least when observing close to Zenith, to avoid 
vignetting from the slit?  

I think this is a very wide slit if the diameter of the dome is, say, 
300 cm (118"). That is 38% of the diameter of the dome.

What am I missing? Or do people live with that vignetting?

Best regards,

Niels Foldager




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