To minimize drafts and humidity when the dome is closed, the ScopeDome manual recommends capping the top of the crown with a ring of sheet metal that extends horizontally to the lower dome casing.
The spider with the secondary mirror removed. The three-element flat field corrector is visible in the spider’s center gives an 80 millimeter flat focal plane. The entire assembly as pictured is 13 kilograms.
The photo below shows the optical tube assembly (OTA) configured for prime focus flat-field photograhy. The secondary mirror is removed so that the light path passes through the flat field corrector and filter wheel.