wildcard wrote:Attached is a one page PDF document that had been uploaded by user "obsessionowner" on the Argo Navis Yahoo Group entitled
"How to Center the Encoder Bracket on the mirror box" by Charlie Starks and Jean-Paul Richard.

Thanks again, Gary!

ausastronomer wrote:
Firstly, if you can't adjust the altitude encoder position in both axes you don't have any options that don't involve a lot of work on the mount. On a scope like an Obsession (which is what is pictured in Scott's powerpoint) it is very easy. Scott's powerpoint is very detailed and actually makes the process sound a lot more complicated than what it is.

Hi John - Thanks for the amplification on the red-laser method.

Unfortunately, I can not easily move the ALT-encoder on this scope. But the first task is to determine if there's a substantially better location and therefore worth the effort so I appreciate your help.

Cheers,
Mike

Gary - Thanks much for the PowerPoint! I'll take a look.

Mike

ausastronomer wrote:Hi Mike,

Notwithstanding that your altitude bearings are eccentric, have you done the red laser test to ensure that the altitude encoder is centred, as best as can be centred, on the altitude axis of rotation? I found this helped pointing accuracy enormously in the pre TPAS days. It also helps post TPAS as there are less errors to be corrected by TPAS.

If you haven't done it I can walk you through it.

Hi John! Rosalie says Hi! too. Hope you are well. We are traveling to NZ this spring (I'm taking the travel scope that's the subject of these posts). We haven't yet visited all the places you recommended for our last trip!

Thanks for the kind offer to help. I don't know the red laser test, but it looks like Gary posted a how-to guide so I'll take a look at that.

I discovered this problem because I could see that the ALT-encoder was moving as I moved the scope in altitude. I set out with paper and protracter to find the "right spot" but discovered there wasn't one right spot. But, as you say, there is probably a "best" spot.

Many thanks,
Mike

Hi Gary: Yep, I’ve performed a Daytime Encoder Test. This scope started out with awful AZ encoder reproducibility, but with work I now have 360-degrees of revolution registering as 360-degrees on my AN and all of the results I discuss were obtained under this condition.

The important observation out of my data is that the scope has a raw-rms of 20’ whether I do an "all-sky" sampling run or a “restricted-sky” sampling run. IOW, it is NOT the case that I get a small model-rms with the restricted-sky run because I started out with a small raw-rms. Rather, BOTH all-sky and restricted-sky samples start out at 20’ raw-rms. The best-case model-rms values are 10' for the all-sky sample, 2.5' for the restricted-sky sample. That’s why I suspect going forward I’ll get a better determination of model term values with the restricted-sky sampling.

Regards,
Mike

Test
Test

Thanks for setting this up, Gary.