Thursday, April 29, 2010

collimated Centre Dob

For the RASC Toronto Centre's loan program 8" Dobsonian, I made a "collimation cap" with a film canister (weird, I have lots of these "antiques"). Popped it in the eyepiece tube. And saw it was off a little (explains my less than good views). The secondary was OK but the primary was out.

I looked at the far end. Was not sure how to adjust the Philips and hex head screws at the main mirror (who's the goof who designed it such that you need 2 completely different drivers?!). Downloaded and printed the Sky-Watcher docs. The hex heads are called the "locks." In fact, they push the mirror "in" (toward the secondary); while the Philips screws pull the mirror out. Tried to collimate but it didn't seem to be working.

I noted that there were two rubber grommets on 2 of the Philips and none on the last one. I also noted that the hex head grubs were nearly at their maximum extension (they're only a 1/4 inch long). Could they fall out?! It seemed that if there weren't 2 grommets then the mirror cell would be closer to the back plate and the grubs wouldn't extend so far. I removed one of the double grommets and transfered one to the empty spot. Then completed the collimation. Nearly perfect.

Wondered if the horizon-to-horizon blue sky would last...

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