Dithering ruined my night!

[Guest Tuomo]

Hello!

 

New imaging season has launched and I was about to capture double cluster. I have been able to get relatively long exposures with my belt driven AstroEQ EQ5. With guiding, easily over 300 seconds. Thats pretty much the upper limit in my light polluted garden. Last week has been nearly perfect for AP. Nearly perfect seeing for many nights....

So, as I started guiding, first there was strange problem with symmetrical graph. When RA moved to north, DEC moved to south and it was perfectly in sync....I disabled DEC compensation in PHD2 options and everything started to work with no problems...huh?.... After that I could not believe my PHD2 graph. DEC and RA graphs under 0.5" and line was VERY flat, easily the best guiding done with my new nema 17 steppers and I was not guiding dead pixel. I let PHD2 to run quite some time just to make sure everything was for real. It was not a dream and I was about to to make first exposure. After the first exposure there was dithering and after that it ruined everything. Dither did its thing but guiding was not able to recover from that. Ok, first I was thinking that the movement was too large for guiding to catch up, but after I lowered scale and dithering distance there was more problems. Guiding and basicly everything was random from that point on. Guiding was erratic and at the late hours even symmetrical just like before. When RA moved, DEC moved in symmetrical fashion. It felt like there was constant dithering going on and I could not stop it.

So here are my conclusions:

I tried to PA so that there would be constant drift to north or south. I dont know how to do this so in Pole master I never centered those red and green squares. I left one square at the top of another assuming there would be drifting. HOW do I polar align that there is some drift to north or south?

Scope is balanced and mount is leveled. To be honest Im getting tired of these RANDOM things with my modded EQ5. 

 

ps. There is guide log in attachment. You can clearly notice the first symmetrical guiding error and after that VERY flat line(there was few times I had to make small adjustments to focus, so that why there are few big jumps in that flat line. After dithering everything is just chaotic and I tried to do everything to stop it. There was one lonely cloud that interrupted my guiding but that passed, thats why the star loss. IF weather allows it I try to guide tonight. I hope it was some kind of software glitch, but for some reason I doubt that....Do you guys at SGL have ANY idea what was going with my guiding.....

log.rar

[ollypenrice]

Being slightly polar misaligned is all you need if you want to guide in only one direction in Dec. You have to experiment to see which Dec guiding direction it is that can be disabled. After a meridian flip you must swap the guiding direction round to the opposite one.  This is sometimes done on mounts with backlash in Dec. If your mount doesn't suffer from Dec backlash then you should get your polar alignment to be as good as you can. You may be trying to solve a problem which doesn't exist.

Did you run the guiding assistant after calibration? This is a good idea and works well. Let it run for several minutes and then apply the settings it recommends.

If you have problems with automated dither you can just move the mount very slightly between subs by stopping the guiding and giving the mount a tiny movement via the handset at guide speed. 

But first I'd see how things work out with a good PA.

Olly

[Guest Tuomo]

On 28.9.2017 at 18:43, ollypenrice said:

Being slightly polar misaligned is all you need if you want to guide in only one direction in Dec. You have to experiment to see which Dec guiding direction it is that can be disabled. After a meridian flip you must swap the guiding direction round to the opposite one.  This is sometimes done on mounts with backlash in Dec. If your mount doesn't suffer from Dec backlash then you should get your polar alignment to be as good as you can. You may be trying to solve a problem which doesn't exist.

Did you run the guiding assistant after calibration? This is a good idea and works well. Let it run for several minutes and then apply the settings it recommends.

If you have problems with automated dither you can just move the mount very slightly between subs by stopping the guiding and giving the mount a tiny movement via the handset at guide speed. 

But first I'd see how things work out with a good PA.

Olly

It was the loose RA belt wheel that caused everything. Not Dithering. Sorry Mr. Dithering...At the moment guiding works fine. Thanks for your help and time.