LXD75 Polar scope centering
Posted 07 October 2013 - 12:11 PM
I've found that my polar scope is off-center, and can't get a good polar alignment because of it. However, I'm having a fit centering the polar scope to where the cross hairs of the scope correspond to the center of rotation of the mount. Is there anybody who can refer me to a website or explain the technique for calibrating the polar scope center to the mount RA center of rotation. I'm not looking for info on how to use the polar scope once it's calibrated since I know how to do that. I'm guessing that it starts with pointing the polar scope at a fixed distant target. Then there's some combination of using the mount alt-az adjustments along with adjusting the 3 polar scope centering screws, but I'm having trouble figuring out the combination.
Posted 07 October 2013 - 12:55 PM
Posted 07 October 2013 - 02:43 PM
However, if the reticule housing is not collimated to the main objective you'll never get it right... BTDT...
Posted 07 October 2013 - 03:45 PM
OK, I finally found a web page - does anybody have a better technique?
Michael, the centering technique does work if the polar scope was properly assembled at the factory. A number of them were missing a critical part...the large o-ring on the inside of the mount (on the end of the polar scope). The o-ring serves as a pivot point for your polar scope as you adjust the three screws. Without the o-ring and pivot point any attempt at alignment will be hit and miss (and temporary).
Setting up and testing dozens of LXD75 mounts while working at Meade, I never used the polar scope. It was easier to make sure my OTA and mount were well aligned and then use the iterative technique for polar alignment.
Posted 08 October 2013 - 01:22 AM
I've added a collar to the front of the scope to stabilize it in the hole in the RA axis. I'm really looking to get a good polar scope to make the setup fast for the mount. I can use a slower technique for astrophotography, but I really want something fast and reliable for quick setups. I've read that the Takahashi NJP polar scope is good enough to use for astrophotography, so I'm building my own higher precision polar scope. Right now, I'm evaluating the current adjustment setup to see what works and what doesn't, and centering the crosshairs is really dicey. I've got an idea for the new polar scope which has a dual opposing cone design, but I'm also thinking about building an addon to the current polar scope collar that allows more precise adjustments.
My polar scope DIY thread is here: