Andrew Celestron CPC-1100 Celestron NexStar 8SE OTA on Sirius EQ-g mount running EQMOD Orion ST-80/SSAG guiding package Coronado PST on iOptron SmartEQ Imaging Source DBK21AU04 and DMK41AU02 Mallincam Hyper Color imager My astronomy blog: http://andysastro.blogspot.com Norman OK (nearest CSC station) 73 de AE5YJ
Quote:It means the polar scope's optical axis is not in line with the scope's mechanical RA axis.
When adjusting, only adjust half the distance you think you should, and you will find that you will not have to adjust as much as you think you will. Here is a good tutorial:
Uncle Rod Uncle Rod's Astroblog: http://uncle-rods.blogspot.com/
Tak AP QSI Canon
Quote:As a side note. When I had an EQ-G I found the plar alignment routine in Eqmod extremely useful. It's incredibly easy to use and it gets you reasonably aligned in minutes. At least close enough for guided imaging.
Quote:The correct way to align the polarscope's reticle is to center the crosshairs on a target and rotate the mount on the RA axis. You'll need to point the mount at the target using the altitude and azimuth adjustment screws or by rotating the tripod and adjusting the leg lengths.
Now, as you rotate the RA axis, any movement of the crosshairs on the target means that the reticle needs to be centered a bit better. As Orion said, you use the adjustment screws on the polarscope. What Orion didn't tell you is that you can't adjust the reticle by tightening the screws. You need to loosen two or three adjacent screws before tightening the other or others. The screws press directly on the edge of the reticle and overtightening them can crack it. You really don't want to do this.
Your description of how things looked through the polarscope sounds like you have it perfectly aligned with the mount's axis. If objects viewed in the scope describe an oval, then you probably have cone error, caused by the scope's axis not matching the mount's. Orion's Vixen dovetail bar that the rings attach to has adjusting bolts where the rings are connected to correct cone error. You should use a target at least 500 yards (1000 or more is better) away when checking for OTA (Optical Tube Assembly) cone error. A scope with zero cone error has its optical axis perfectly aligned with the mount's RA axis.
A final thought - think about what happens when you collimate your scope. What happens to its optical path as you collimate? Could this introduce cone error? I'll leave it up to you to think about these things rather than spend more tome adding to this response.
Warren - Stargazing since the 60's! Scopes: ETX-LS6, ED80T, AT6RC, Lunt LS60T, C9.25 Mounts: Atlas EQ-G, Vixen Portamount II Cameras: Atik 314L+,DMK31AU03,SSAG, ASI120MC Filters: Astrodon LRGB, Orion HA, SII, OIII Acc: Orion 5 place Filter wheels x 2, Flatman Primary Imaging site: Bortle Scale Class 6 Red Zone http://astrobin.com/users/rigel123/
Quote:I had the same experience as you. When I finally aligned it on a radio tower about a half mile away I could get that rotation you are seeing down to a minimum. This gets me close enough that I don't drift align after doing alignement with the PA and I can do 2 minute unguided and pretty much as long of an exposure that I want guided. I typically don't go over 15 minutes but could go longer guided.So if you haven't tried this on something further away, try that first.