PHD Guiding - How good is good enough??

[Peje]

As title suggests I'm trying to figure out if my guiding is good enough, I've attached a graph from last night with some fairly OK conditions (no wind but high level cloud) which would be fairly typical of a nights guiding for me. I typically stay within +/- 1 arcsec and on a really good night I would sometimes see long periods of within +/- 0.5 arcsecs.

My setup includes a 20+ year old steel tubed Newtonian with non-CNC tube rings (I couldn't get CNC ones for this oddball size) so it's optics/construction are likely to be less than perfect. I am fairly certain I'll be getting lots of flexure but I'm not planning to fix this as I've set on upgrading the scope to a Quattro 10 CF next summer, I did plenty of upgrades this year so I wanted to reap the benefits of these before chucking even more money at a new scope.

Results are fairly round stars depending on conditions, I will get obrounds and odd halos but I think this is not directly related to my guiding as it seems to be consistent (per night) regardless of how the guiding is performing.

Thanks in advance,
Pete.

[Peje]

@Shelster1973

[Freddie]

I guess only you can determine what is good enough based on what you find to be acceptable to you in your images.

[Peje]

LOL I kind of expected that answer, I guess a better question...what values do others find acceptable?

[cfpendock]

It seems pretty good to me.  You are guiding well within the limits of atmospheric seeing, and I don't know if it would be possible to do better much than this. I would be tempted to increase the exposure time to at least 5 seconds.   At the end of the day, it is pixels rather than arc seconds that count, and as Freddie above has pointed out, it depends what you want from your images.  

Chris

[Starlight 1]

I put this in a post this week and there is lot more to think about ." There is a sticky somewhere on this forum explain in great lengths on the telescope size against the guide  size ,pixel values, and trying to stay within whatever percentage. "

[Peje]

15 minutes ago, Starlight 1 said:

I put this in a post this week and there is lot more to think about ." There is a sticky somewhere on this forum explain in great lengths on the telescope size against the guide  size ,pixel values, and trying to stay within whatever percentage. "

Any chance you remember the name of the topic so I can have a read?

Ideally I'm just trying to figure out if I'm in the right ballpark or if I have work I need to do before the still and clear nights (hopefully) arrive.

[Peje]

16 minutes ago, cfpendock said:

It seems pretty good to me.  You are guiding well within the limits of atmospheric seeing, and I don't know if it would be possible to do better much than this. I would be tempted to increase the exposure time to at least 5 seconds.   At the end of the day, it is pixels rather than arc seconds that count, and as Freddie above has pointed out, it depends what you want from your images.  

Chris

I'm generally doing deep space and normally fairly long (~8min) exposures. I haven't tried going above 3 seconds so perhaps trying 5 might give me some improvement.

[Starlight 1]

I see this over a year ago Peje  sorry .

[Starlight 1]

I push my heq5 mount from 20 mins to 1 hour on a clear night.

[Peje]

5 minutes ago, Starlight 1 said:

I see this over a year ago Peje  sorry .

No problem.

2 minutes ago, Starlight 1 said:

I push my heq5 mount from 20 mins to 1 hour on a clear night.

Sorry, not following, you do what?

[Starlight 1]

I can image up to 1 hour subs and still have round Stars.

[Peje]

Good lord, that's spectacular!

[Starlight 1]

This is 900s just staring to go off round.

Eastem Veil NGC6992_900sec_1x1_L_frame2.fit

[Starlight 1]

I allway start out by runing phd for 5 mins to see the best I can get from it every night not the same any 2 nights its down to seeing . so test sub are done to save time . so this 900s sub tell it the best I am going to get on this  night.

[Peje]

That's very impressive, I did look at adjusting my PHD settings but gave up after very little success. Perhaps due to not really knowing what I was doing other than following a youtube tutorial

[RayD]

7 minutes ago, Peje said:

 

That's very impressive, I did look at adjusting my PHD settings but gave up after very little success. Perhaps due to not really knowing what I was doing other than following a youtube tutorial

 

The built in guide assistant is pretty good, and once run for 5 minutes or so tells you what to adjust to improve things.

Worth a look.

[Peje]

12 minutes ago, RayD said:

The built in guide assistant is pretty good, and once run for 5 minutes or so tells you what to adjust to improve things.

Worth a look.

It certainly sounds like it is worth a look, maybe if there's a break in the clouds tonight I'll have a poke at it

[Starlight 1]

I do not like guide assistant and stay away for useing it. I am looking at the blue line how good is your balancing of the telescope  as it puting lots of up in on blue.

[Peje]

2 minutes ago, Starlight 1 said:

I do not like guide assistant and stay away for useing it. I am looking at the blue line how good is your balancing of the telescope  as it puting lots of up in on blue.

My balancing is pretty good, I generally off-balance the weights to make it west-heavy but it doesnt seem to make any difference.

[Starlight 1]

I make that East by just abit. Your RA try taking it down from 70 and try 25 to 40 and the same on the next one that is on 10 . It look to be push blue hard  and try to take away again pust it back down .

[Peje]

2 minutes ago, Starlight 1 said:

I make that East by just abit. Your RA try taking it down from 70 and try 25 to 40 and the same on the next one that is on 10 . It look to be push blue hard  and try to take away again pust it back down .

OK, you reckon I should try RA Agression to 25-40 and Hysterisis as 25-40?

[RayD]

Personally I would say your RA RMS @ 0.60" is very reasonable, and should be good for all but the most demanding imaging.  I achieve about 0.4" with no drift alignment and have no issues imaging 900s+ with pinpoint stars.  However, if anything I would say the oscillation on the RA axis would say to me that you could try a touch of bias on the East side to balance slightly heavy on this side of the pier.

[RayD]

13 minutes ago, Peje said:

My balancing is pretty good, I generally off-balance the weights to make it west-heavy but it doesnt seem to make any difference

I think this should be East heavy (depending what side of the Meridian you are imaging) and could account for the RA oscillaiton.

[RayD]

In addition to moving the weight bias (this only needs to be very slightly East heavy, not too much) I would definitely judge how well your guiding is by the images you're getting, not just the shape of the graph.  Whilst this can tell you a lot, it also is just showing you that your guiding is actually working.  

Olly Penrice (I believe one of the more respected imagers on this forum) recently suggested in another post using the guiding assistant, and notes how it helped him, so it's worth looking at.