Posted: Jun 14, 2020 1:34 pm
by theropod_V_2.0
One other thing:

CAT scopes require a “cool down” period before they start to really providing good images. The larger the scope the longer it takes to reach this equilibrium, and the upper end sizes can take HOURS to get right. If the night time temps drop quickly for a long time a big CAT might never equalize its internal temperature with the ambient air temp. Most of the reason for this is the sealed construction of the design. A Newtonian has a huge hole in the “objective”end and heat just flows out like water, and refractors have their objective lens directly exposed to the air. Some people remove the eyepiece and turn the OTA (Optical Tube Assembly) objective down so the residual heat has an escape path, but that scares the hell out of me as it breaks the seal and could allow foreign debris to get inside the scope. A CAT is very touchy when it comes to alignment of the corrector plate with the main mirror, and internal cleaning is something I would leave to a paid expert. With proper care it is possible that such internal cleaning to never be needed. I personally absolutely love CATs and MAKs. The short OTA is easier on the mount and wind has far less surface area to work on, and wind with a wobbly mount is a study in frustration.