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C11 Mechanical Alignment & Collimation

Details of back cell casting

The C11 was fitted with two fans for cooling and three mirror lock screws to support the primary once in focus. The primary mirror is a big heavy piece of glass and these scopes by design have a known problem holding focus and collimation with weight shift when slewing in different parts of the sky, usually enough to throw the collimation out by a lot. So locking the primary on three points to support it helps hold it in place and minimise these issues.

Tube current can be a problem as well when the temperature drops rapidly in the evening. Fans help recirculating hot air out of the tube much faster and cooling times are improved.

A couple of handles on the back casting cell help with handling the scope as these can be quite heavy. It's easier to grab two handles and move the scope manually on the mount rather than trying to hold the sides of the casting, These handles are originally bathroom vanities door handles.

Finally a micro-focuser is a must and allows for very fine adjustement of the primary. The stock focuser is too coarse. You wouldn't be able to focus accurately with one, especially when using the hyperstar. The critical focus zone (CFZ) is pretty tight at F/2 in the order of 50 microns.

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Details of back cell casting