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I collimate my scope every time I set it up. So i've had lots of practice.

But I can use a sight-tube. My eyes cant focus on the mirror and the cross hairs at the same time. I've used a chesire, but i find them to be a pain. I have an auto collimator, but I don't use it. It's extremely sensitive to focuser tilt, which for a visual scope is not a critical adjustment.

I can however show you how to collimate with a barlowed laser (mine). It's the quickest method I know. I've compared it to cheshire collimation and find the barlowed laser to be just as accurate.

Come to the next Carp star party. And I'll show you how I collimate my scope and you can try the method with yours.



As for fan cooling:

if you're blowing against the back of the mirror a 120mm computer fan will suffice. But you should turn it off when doing planetary observations. I would also recommend filtering the fan intake. (You will be amazed how quickly the filter gets filthy.)

If you're sucking air out of the tube, I suggest a big a fan (or as many fans) as you can get. The key in this case is to seal the bottom of the tube so the fan(s) dosent(dont) use suction.

If you have a choice sucking is probably better than blowing. But it it is harder.

The very best fan arangement is fans that blow straigh across the front of the mirror. This is the mist effective arrangement as it produced instant results (the key is to thermaly-homogenize the air infront of hte mirror. do that, and you dont actually need to cool the mirror). However it's the hardest to mechanically implement. It hink filtering is especially important in this case.

I use a filtered-back blowing fan on my 25" because I havent figured out how to arrange surface scrubbing fans on my 25" whithout hacking the nice wood to bits.

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