Long exposure guiding

[Bottletopburly]

So Friday night was a good fruitful evening, earlier in the week I had to fettle the pier plate as Mount wasn’t sitting flat and riding in the middle of plate , so re  polar  aligned using sharpcap pa and said was GOOD , now I stuck at 120sec subs but I did try 300sec but stars starting to look eggy so stayed on 120 sec , so what’s the secret to getting longer subs , is it down to PA , guider scope?  I use a qhy miniguide scope fl 130mm F5 or should I be using an OAG  on the 200pds F5 1000fl or any other tip.

[+RonC]

Hi Dave, I don't think there's a secret, a good PA (I only use my eye through the polar scope!) a good mount and a  good star alignment (2 or 3 star). I can get 300 - 450 secs on a sub but usually use 180-300 for DSO's using a 150PDS and a mini guide scope..

 

Ron

Edited July 8, 2019 by Ron Clarke

[+Ibbo]

Mount with low periodic error, polar alignment (I use Sharpcap on the mobile and drift align on the permanant set up)

 

Star alignment helps find objects but does nothing for guiding.

A GEM does not need to be level.

 

Guider should help even at 1m f/l do not guide with very short guider exposures as you chase the seeing.

 

Personally I use an OAG but I do image at near 2m f/l sometimes and my camera has it built in.

 

Make sure things are nipped up (not too much though) and watch out for dragging cables, but do allow a bit of give.

 

 

[+Ibbo]

Balance the mount with a slightly heavy east side.

[Bottletopburly]

2 hours ago, Ibbo said:

Mount with low periodic error, polar alignment (I use Sharpcap on the mobile and drift align on the permanant set up)

 

Star alignment helps find objects but does nothing for guiding.

A GEM does not need to be level.

 

Guider should help even at 1m f/l do not guide with very short guider exposures as you chase the seeing.

 

Personally I use an OAG but I do image at near 2m f/l sometimes and my camera has it built in.

 

Make sure things are nipped up (not too much though) and watch out for dragging cables, but do allow a bit of give.

 

 

I used 3sec last session 

2 hours ago, Ibbo said:

Balance the mount with a slightly heavy east side.

Even on a belt modded mount 

[+Ibbo]

11 minutes ago, Bottletopburly said:

I used 3sec last session 

Even on a belt modded mount 

I would as it still has a worm in the mix

 

[+Graham]

No one has yet mentioned the most basic and fundamental step in guiding.

 

Calibration is key to good guiding.

 

The more steps used when calibrating the more calibration data collected = the smoother the guiding.

 

By personal preference I use PHD 1 

 

I am set up so the calibration steps in RA are between 20 and 30 depending on which part of the sky I am imaging in. ( and yes it does differ greatly as you move up towards the zenith )

 

The following adjustments will be found on the guiding graph window.

 

Once guiding you need to adjust the RA aggressiveness to control the over corrections that might occur. 

I have mine set at 60.

I will adjust this as and when to suit the conditions. 

 

You can also set the HYS. this also helps to correct oscillation caused by the over corrections.

I have mine set to 12.  

I will also adjust this as and when to suit the conditions. 

 

You also have the ability to change the pulse width in EQMOD to suit your mounts characteristics.

On my AZ EQ 6 I have these set at 50 in RA and 70 in DEC 

 

I also use OAG which again is a personal preference.

I run at 1 second subs which is my preferred setting.

 

Apart from the odd glitch caused by outside sources such as temp changes, moisture, wind ect.  I can happily run at half hour subs with a near flat lined graph all night.  

 

This won't happen overnight it takes time, effort and above all patience --- lots of patience ---- oh and a great deal of swearing too ?

 

Take the time to experiment with these adjustments so you can fine tune your guiding to your own set up.

Remember too if you strip your set up down after every session these parameters will also change slightly every session.

Edited July 8, 2019 by Graham

[+Ibbo]

Yes I forgot the important bit

 

the swearing

[Bottletopburly]

1 minute ago, Ibbo said:

Yes I forgot the important bit

 

the swearing

i covered that base many times 

[Bottletopburly]

22 minutes ago, Graham said:

Calibration is key to good guiding.

yes calibration done .

 

23 minutes ago, Graham said:

By personal preference I use PHD 1 

using phd2 though maybe i should try phd as less to setup than phd2 ,i do have it all set up 

 

27 minutes ago, Graham said:

I am set up so the calibration steps in RA are between 20 and 30 depending on which part of the sky I am imaging in. ( and yes it does differ greatly as you move up towards the zenith )

w-15 steps E 10 steps N 11 steps s- 9 steps backlash 4 steps / phd2 calibration ar 20 degrees ish it then works out and allows/adjusts for declination 

 

30 minutes ago, Graham said:

You also have the ability to change the pulse width in EQMOD to suit your mounts characteristics.

On my AZ EQ 6 I have these set at 50 in RA and 70 in DEC

cant remember off hand did adjust to what you told me before 

 

32 minutes ago, Graham said:

Once guiding you need to adjust the RA aggressiveness to control the over corrections that might occur. 

I have mine set at 60.

I will adjust this as and when to suit the conditions. 

 

You can also set the HYS. this also helps to correct oscillation caused by the over corrections.

I have mine set to 12.  

I will also adjust this as and when to suit the conditions. 

yes i never know which way to adjust higher or lower 

[Bottletopburly]

 phd2 guide log from last session https://www.dropbox.com/s/hngi39y3ptr3uom/PHD2_GuideLog_2019-07-05_212119.txt?dl=0

i remember looking at the rms value whilst guiding it was lower than what the log was telling me 

ran guiding wizard too and dark map also done .

Edited July 8, 2019 by Bottletopburly

[+RonC]

Graham are your PHD settings for Pulse or ST4?

[+Graham]

They are for pulse guiding the Az EQ 6 via EQMOD

Edited July 8, 2019 by Graham

[+Graham]

" w-15 steps E 10 steps N 11 steps s- 9 steps backlash 4 steps / phd2 calibration ar 20 degrees ish it then works out and allows/adjusts for declination " ? ? ?

 

My exact reason for using PHD 1

Select star - hit calibrate - guiding 

 

[Bottletopburly]

33 minutes ago, Graham said:

My exact reason for using PHD 1

Select star - hit calibrate - guiding 

i will try it next time out 

[+RonC]

That's why I like PHD 1.2 even though I use ST4 ?

[Bottletopburly]

8 hours ago, Graham said:

" w-15 steps E 10 steps N 11 steps s- 9 steps backlash 4 steps / phd2 calibration ar 20 degrees ish it then works out and allows/adjusts for declination " ? ? ?

 

My exact reason for using PHD 1

Select star - hit calibrate - guiding 

 

You only have to calibrate the once though in phd2 @Graham , move to a different target , select star, guide 

[+RonC]

I do that with PHD 1 but not if it's the opposite direction to the previous target, if I'm imaging then I'll re-calibrate

to make sure it's still accurate. 

Ron

[+Derbyshire Dave]

Interesting comment that a GEM doesn't need to be level. I always use a spirit level and set mine as level as I can in both directions.I used 3sec last session. I use PHD2 and always force a re-calibration by holding the shift key down when clicking the guiding symbol.

 

22 hours ago, Ibbo said:

Balance the mount with a slightly heavy east side.

 

What are the practicalities of 'Slightly Heavy East Side'. I understand that it's to keep a bias, but how do you actually do that, and by how much?

 

 

 

 

[+Ibbo]

As long as the polar axis is pointing at the north celestial pole ( for us)it does not matter if the tripod is upsidedown, it would make it awkward to use granted but the PA would not be out.

 

The weight bias is so that the worm is always in full contact  with the cog esp when imaging near the meridian.

Edited July 9, 2019 by Ibbo

[+Derbyshire Dave]

Thanks Steve. OK, so I'm polar aligned, telescope pointing West, camera on the 'Eastern' end, do I bias it so that it's slightly 'camera end' heavy?

[+Ibbo]

I would bias it to camera heavy, you don't need much 1/2 kg is fine.

 

For me it really helps when I am in what I call the dead zone ie near the zenith near the meridian is where my mount plays up.

I also have mine a bit tail heavy as well.

 

And to confuse things more I also turn off guiding Dec in one direection as it can "bounce" ans upset the guiding.

 

All good fun and nedds to be experimented with for your mount as they all behave slightly differently.

Edited July 9, 2019 by Ibbo

[+Derbyshire Dave]

Yeah, it is all interesting. Guiding is a funny old business, and I tend to leave well alone.

 

This thread has made me want to go and try some of these things out.

 

[+RonC]

Good luck Dave!!

[+Ibbo]

Its all witchcraft I tell you