Tonight the seeing (according to Clear Sky Chart) was supposed to be poor. I took some exposures and measured the FWHM in PI and it showed about 3" - so the seeing is poor.
I decided just to play with PHD2 settings to see what would happen with different settings. My question is what (aside from round stars) should I be looking for on the graph visually. Do I want the flattest RA/Dec lines I can get with the minimum amount of corrections? How do you know if you have achieved this?
Here is my log from tonight - do you see ways to improve or is that as good as I can get on a poor seeing night?
I’m using a good mount (AP 1100GTO with an OAG on a C11 at 2800mm) no PEC correction being used.
On my Paramount - with ProTrack enabled, I achieve about 0.3" RMS - with 8-second exposures (remember, short exposures progressively measure seeing more than actual tracking errors)
On a belt-drive Avalon mount, which normally has about 10" pk-pk PE, I achieve about 0.6" - with 1-second exposures. (This mount has faster changing tracking errors and needs short exposures to keep up)
My seeing conditions are average - I’m at sea level in a country town in the UK.
You should aim for having sharp pictures without any noticable trailing stars… forget about the guiding graph. If the photo’s look fine, it’s fine. If not, then you can trouble-shoot and any problems can be caused by a lot of things.
My AZ-EQ6 was (pure luck) very good to begin with, on a clear night without wind I could achieve 0.5" guiding. I did decide to take it apart, clean it and replace some parts because I wanted it to behave like that in all positions (which it wasn’t always). I tweaked the backlash as well etc and I still get the 0.5" guiding (fjew) but it behaves better in general. I have to mention though this was a replaced unit, the first I bought simply had a major problem in guiding and to convince the store that was the case was a whole different and interesting road. I knew it was the mount itself because I was taking away all kinds of variables and the problems persisted, I went to stand next to the mount to watch the guide graph on a remote tablet and heard noises when things started to fail. Thing you have to realize is that guiding is an extremely precise thing to do, placing your foot next to the mount was enough for me to see the effect on the graph, so you really have to think about every little detail in the entire process to figure out where things go wrong… can be very frustrating, but you also learn a lot.
Well - that depends on how good you want to be - if you can see trailing stars, you certainly do not need a graph but when you are pushing the quality envelope, a guiding graph, with a suitable exposure period, is more discerning. I doubt many can see a 10% eccentricity on a star, but when you combine R, G & B exposures and try and line up stars - you wonder where the uneven color borders come from…
Yes indeed, so it depends on what you’re trying to achieve. If indeed there’s a problem in the final picture, that’s reason to get towards trouble shooting the guiding… but there are way too many people (me included in the beginning) that just want to get that RMS number as low as possible while it doesn’t always make any difference.
I knew it was the mount itself because I was taking away all kinds of variables and the problems persisted, I went to stand next to the mount to watch the guide graph on a remote tablet and heard noises when things started to fail. Thing you have to realize is that guiding is an extremely precise thing to do, placing your foot next to the mount was enough for me to see the effect on the graph, so you really have to think about every little detail in the entire process to figure out where things go wrong… can be very frustrating, but you also learn a lot.