One thing we didn't talk about is your guider setup. Are you using an offaxis guider or a guidescope? Guidescopes are subject to differential flexure. Offaxis guiders are usually way superior.
Here are fairly common settings:
1. The better the mount and the better the polar alignment then you tend to use longer exposures on the guide camera and shorter exposures if all is not good. By longer I mean 6 seconds which is what I find works best on the better mounts. What works for yours is trial and error. I used to use 1 second with a Tak NJP mount.
2. Guide rate .5X. Some mounts have some backlash so you can put in say a 1 second delay between corrections to help with that. Some software lets you set the aggressiveness separately for the 2 axes, others don't.
3. Aggressiveness. Similar to the above. The better tracking the less aggressive it needs to be. Again a bit of trial and error and watch the guiding errors. But 6 is setting I use a lot. You can raise that if the seeing is good.
If the seeing is bad you don't want to be chasing the seeing so watch the corrections and if they go from - to + a lot then you are chasing the seeing and the mount is correcting some of the last correction instead of the seeing.
4. Min/Max: Min: something low like .1 Max 2 to 3. If your polar alignment is good and your tracking is good then you don't want a correction for an error of 3 - its probably PE or a wind gust so set it at 2 so larger "errors" are ignored.
5. I find with PEC the reported errors can get high for a little bit and then lower and that is the PEC kicking in and correcting the larger wave of errors the worm cycle is producing.
6. One of the first things I do if I get too large errors is select another star.
You don't want too bright a star. A nice semi bright star is ideal especially if some light cloud goes over.
7. Roland Christen from AP recommends calibrating your autoguider near where the celestial pole and the meridian intersect.
8. AP has some other informative things about tracking. Like don't have all your counterweights at the bottom of the shaft. Its better to have more weight and have it near the top of the shaft and one weight down near the end of the shaft to get balance as there is less resistance to movement.
Ideal balance is not perfectly balanced but slightly biased to mesh the gears in east/west, I think its to bias towards the west and similarly bias the weights towards the camera. RA and Dec autoguide differently.
There is an article about these points on the AP website I think its under "technical".
Pulse guiding through Ascom is supposed to be superior to ST 4 relay guiding.
I use both an SBIG STi guider and an ASI290 which is very clean and very very sensitive so getting a guide star is easier.
Greg.
Quote:
Originally Posted by Craig_
Cheers!
Hi Greg,
Thanks for the reply.
Unfortunately my perfectionist nature when it came to landscape photography carried over into astrophotography as well - I can't deal with any visible elongation  I must admit that in the one set of data I did stack from it, the elongation in the final stack was hard to see, but as long as it remains I will just have a nagging feeling that I need to fix it.
Re: PEC on mount - if I am honest, no idea. I will need to look at this next clear night. Soon I will be able to image with the EQ6-R + Esprit 80 simultaneously with another EQ6-R and Esprit 120 which should help my patience with fixing the issues I have on the 120, as I won't be wasting good imaging time on the 80.
Mount is only about 8 months old - no upgrades. I'm not aware of any upgrade kit for it but could be wrong (since it already uses a belt.)
Autoguiding - mostly default settings actually. Those have served me fine on the Esprit 80 but clearly not so fine on the 120, but unfortunately I am a bit lost as to what to adjust, when, and by how much. PHD2 is what I am using. Any good resources you know of on how to fine tune your guiding via settings? I mean the manual explains each setting but I guess it's the effect each setting has on other settings and such that leaves me a bit lost when stepping outside the default.
Seeing was pretty good that night from memory but I am no expert in judging it either.
Cheers for the help! |