I just picked up an XT10plus and am looking at picking up a cooling fan for it. I haven't had a problem yet (other than getting a fair amount of moisture on the outside of the tube), but am new to this hobby and want to be proactive. In reading the instruction manual for Orion's fan, it states...
"The cooling fan should be turned on as soon as the telescope is brought outdoors before observing. It should run for approximately 15-30 minutes to properly cool down the telescope. During observing, the fan should be turned off. This is because even though it runs free from vibration, the air currents it generates in the optical tube will degrade image quality. Once the mirror has cooled to the outdoor ambient temperature, the fan will not be needed again until your next observing session."
I see a lot of discussion about what fans to use (computer, etc) and how to mount them to minimize vibration. But according to these instructions, that shouldn't even be an issue.
Congratulations on your new scope.. It's a good one..
As far as Orion Instructions, that would not work for me. This is what works for me with my 10 inch Dob:
- I try to set it out about an hour before sunset and start the fan cooling the scope. Even in San Diego's mild climate, 30 minutes is not enough.
- Cooling the mirror and scope is important for higher magnifications, the planets, double stars. Ideally the mirror should be within 1 degree C of the ambient air temperature.
- I run the fan continuously. The air temperature often drops during the evening, the mirror and scope need to track the air temperature.
- Vibration is a big concern. There are various ways to mount the fan so vibration is not an issue. I use a fan made by Floyd Blue more than 15 years ago. It's a fully baffle design, it seals the back of the scope so all the air flows across and around the mirror and up the tube.
The fan is mounted to a 0.060" thick piece of ABS plastic and it is mounted to the scope using Velcro. The Velcro provides the vibration isolation. It works, I use 820x on very close doubles, it's vibration free.
The hex bolts replaced the locking screws on the mirror cell. I use them for feet to stand the OTA on the floor.