Tube modifications

Ok, this weekend I would like to add a fan to my tube at the back of the primary. This would require ventilation holes at the front but there is only about 7 mm of spacing around the corrector (Schmidt-Newton scope) so the holes to be drilled could be no more than 4-5 mm. Would 50-60 holes be enough for ventilation?
Thanks for any input..
Nico

Are you sure you need to drill a lot of holes?
You might just need to have a fan and an exit hole for ventilation. They might be able to be made in the end of the tube if there is room there. A smaller computer fan could do the job. I am not sure whether I would add that many holes. I would also have to consider using filters for a closed tube like yours. I would filter the air being drawn into the tube and even have a filter for the exit hole. This would help to keep the dirt from gettin into the closed tube on onto your corrector plate.
Floyd

IF you have to ventilate, you would probably be better off with two, larger holes drilled into the SIDE of the tube about 2" back of the corrector. 50-60 holes around the thin metal supporting the corrector could cause a disaster. Either way, the whole thing will have to have all optics removed and other parts (focuser, etc.) masked off or the shavings from drilling could cause big-time damage. A filtered fan at the back and two filtered holes near the top sounds a lot more feasable.

Here's how it looks; the highlighted part on the rear-end shows the cardboard mirror-protection to be removed so the circular opening can accommodate the fan..
Nico

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