PHD Guiding - How good is good enough??

[Peje]

3 minutes ago, RayD said:

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) suggests using the guiding assistant, and notes how it helped him, so it's worth looking at.

Ill give it a try, conditions here ATM aren't really great for deep sky so might as well do something productive.

Last night I took a handful of 1min exposures of Vega and stacked them just to pass the night...pretty happy with the result for just being a quick session.

[Starlight 1]

You can just put then back it only take 10s or so to see if the line going up or down . I do not guiding assistant as it chance to much in one go . and when it that good by just putting one up or one down is easy to go back.

[RayD]

3 minutes ago, Starlight 1 said:

I do not guiding assistant as it chance to much in one go . and when it that good by just putting one up or one down is easy to go back.

I know what you mean, but as the OP appears to be starting with the adjustments from default, running the guiding assistant first, and then working from there with tweaking would seem to be the best approach?

[RayD]

3 minutes ago, Peje said:

Last night I took a handful of 1min exposures of Vega and stacked them just to pass the night...pretty happy with the result for just being a quick session.

There doesn't seem to be much wrong with the guiding on that.  Do you use a coma corrector?

[Peje]

3 minutes ago, RayD said:

There doesn't seem to be much wrong with the guiding on that.  Do you use a coma corrector?

Yeh I have the Baader MPCC Mk3. I do notice some flare if you zoom in but right now I'm putting that down to my 20 year old optics

[RayD]

No it's fine.  I couldn't work out what the horizontal lines were, but remembered you're using a Newt, so they're probably diffraction spikes.

[Starlight 1]

9 minutes ago, RayD said:

There doesn't seem to be much wrong with the guiding on that.  Do you use a coma corrector?

As Peje said its a handful of 1 min sub . is not guiding about geting long subs .

[RayD]

2 minutes ago, Starlight 1 said:

is not guiding about geting long subs

Guiding is about helping and improving any length subs.  The main benefits will be seen on longer subs, but if you have a poor mount or slightly off PA, then guiding will help full stop.  My comment was meant to be more of a rhetorical statement than a constructive criticism.

I'm not debating anything said, I just pass on advice given to me, and one of those is to use the guiding assistant and then work from there as it's there for a reason and will help establish a base for settings such as Hyst. and agression.

I assume you're far more qualified than me to offer help as I'm relatively new to DSO imaging myself, so I'll leave you to advise.

Pete hope you get it sorted 

 

[Peje]

14 minutes ago, RayD said:

No it's fine.  I couldn't work out what the horizontal lines were, but remembered you're using a Newt, so they're probably diffraction spikes.

Yeh my scope has a single lined spider rather than the 4 way version newer ones seem to have.

3 minutes ago, RayD said:

Guiding is about helping and improving any length subs.  The main benefits will be seen on longer subs, but if you have a poor mount or slightly off PA, then guiding will help full stop.  My comment was meant to be more of a rhetorical statement than a constructive criticism.

I'm not debating anything said, I just pass on advice given to me, and one of those is to use the guiding assistant and then work from there as it's there for a reason and will help establish a base for settings such as Hyst. and agression.

I assume you're far more qualified than me to offer help as I'm relatively new to DSO imaging myself, so I'll leave you to advise.

Pete hope you get it sorted 

 

I've only been at it since last year so I'm definitely still in your camp! I think I'll not my settings and give the guiding assistant a go tomorrow.

[Starlight 1]

Ray  Sorry was not ment to sound that way . and any help is good.

[cfpendock]

1 hour ago, Starlight 1 said:

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

Depending on sub length, round stars don't necessarily mean good guiding.  If the average error is in all directions (e.g. from seeing), you will still get round stars.  Similarly, large errors in all directions from any source, when averaged out during the sub, will also give round stars.

 

[RayD]

7 minutes ago, cfpendock said:

Similarly, large errors in all directions from any source, when averaged out during the sub, will also give round stars.

But you have an image full of fuzzy stars rather than nice pin points.

[Peje]

I think my acheles heel is my scope, it's an old, long steel tube with 20+ year old optics. Unfortunately it is also the basis for all my mechanical stability

[Starlight 1]

 I am not into imaging  hard working geting my head round paint program so I just try to get long subs i  just to put on the computer for a week or so then the bin.

[Peje]

An interesting point I just spotted in a guide, I've only been imbalancing DEC but imbalncing RA is also recommended. Which direction depends on which way your setup is driting, need to find that out!

[RayD]

3 minutes ago, Peje said:

 

An interesting point I just spotted in a guide, I've only been imbalancing DEC but imbalncing RA is also recommended. Which direction depends on which way your setup is driting, need to find that out!

 

This is what we were talking about with the east heavy.  Dec would be North & South, RA would be East & West.  

If you stand behind your pier looking North with East to your right, and your OTA is on your right tracking to the left, then you would need to be slightly heavy at the OTA end (East).  This way it will put your mount in a permanent mesh on the heavy side and help that oscillation on the RA on your PDH graph.

[Peje]

7 minutes ago, RayD said:

This is what we were talking about with the east heavy.  Dec would be North & South, RA would be East & West.  

If you stand behind your pier looking North with East to your right, and your OTA is on your right tracking to the left, then you would need to be slightly heavy at the OTA end (East).  This way it will put your mount in a permanent mesh on the heavy side and help that oscillation on the RA on your PDH graph.

I'm not sure the tracking direction is as simple as that for the N/S imbalance, it mentions the tracking drift due to polar alignment

On 20/06/2013 at 17:12, IanL said:

- The same sorts of consideration apply to the Dec worm and worm gear (unless you are not guiding in Dec of course). You need to imbalance the Dec axis by moving the scope forwards/backwards (or adding weights) depending on which direction you are pointing relative to the zenith so that you achieve driven resistance.

If you have southward drift:

- If the scope is pointing South of the zenith, imbalance the scope so that the North (lower) end is heavy.

- If pointing North of the Zenith, again imbalance so that the North (higher) end is heavy.

If your polar alignment is causing a gradual northward drift instead, then you reverse the imbalance:

- Pointing South of zenith, South/higher end heavy.

- Pointing North of zenith, South/lower end heavy.

 

 

[RayD]

Yes Dec is a little different as if you are perfectly polar aligned, then in theory you should have no movement at all in Dec.  However, if you are struggling with dec then you can balance slightly out again (front heavy) and guide dec in one direction only.

If I were you at this point I'd make sure your PA is as good as it can be, run slightly East heavy to help the oscillation, and then run the guiding assistant.  From there you should be somewhere in the ballpark and can then look at tweaking the Hys and agg settings, and perhaps looking at Dec balance and guiding in 1 direction only in dec if that's still bad.

[Thalestris24]

Hi

On my AVX facing east I usually get between +/- 2" to +/- 4" of guiding error but that's mostly due to imaging through an open window which gives lots of turbulence. If I guide through the window glass I get a much better performance but, of course, stars get distorted! I wish there was something as transparent as glass but without the refractive properties. The heq5 seems to perform better than the avx though that's through a smaller open window facing west where there is less overall lp. Naturally, I stick to shorter focal lengths

Louise

[Peje]

7 minutes ago, RayD said:

Yes Dec is a little different as if you are perfectly polar aligned, then in theory you should have no movement at all in Dec.  However, if you are struggling with dec then you can balance slightly out again (front heavy) and guide dec in one direction only.

If I were you at this point I'd make sure your PA is as good as it can be, run slightly East heavy to help the oscillation, and then run the guiding assistant.  From there you should be somewhere in the ballpark and can then look at tweaking the Hys and agg settings, and perhaps looking at Dec balance and guiding in 1 direction only in dec if that's still bad.

I used Drift Align in PHD a few months back once I moved to the pier and got it as close as I could. Looks like we'll have some cear spells later so I'll have a crack at the guiding assistant

[RayD]

2 minutes ago, Peje said:

Looks like we'll have some cear spells later so I'll have a crack at the guiding assistant

Good luck, let us know how you get on.

[Starlight 1]

I would like to think we all  like to see a good PhD all the time. But it's the image that counts . Just curiosity did you say what pixel scale you guiding at.

[RayD]

45 minutes ago, Starlight 1 said:

Just curiosity did you say what pixel scale you guiding at.

Looking at the OP's sig, it seems the guide scope is a ST80 (fl 400mm) and he's using the QHY 5L ii (3.75um) as the cam.  This would give a resolution of 1.93"/p.

[Peje]

Hi All, out working at this. Typically clouds rolled in right in the middle of the guiding assistant running but I grabbed some screenshots before it all went pear shaped. Do they mean anything to anyone else??

[Peje]

4 hours ago, Starlight 1 said:

I would like to think we all  like to see a good PhD all the time. But it's the image that counts . Just curiosity did you say what pixel scale you guiding at.

I tried changing RA aggression to 25 & 45 but it started to drift off wildly so had to change it back. Worth a try though, thanks