For my next installment of learning!...

[Rustang]

I'm trying to use my down time as productively as possible so I'm now going to try and understand my guiding graph/settings a little better. Up until now all Ive known really is to make sure the TOT reading stays under 1 and your good!, it has been doing that fairly well, keeping between 0.4-0.8 most if the time but really does get upset sometimes and as you can see from the picture, the graph gets pretty crazy.

Ive been doing a lot of reading myself and have read that if its doing this I can lower the 'RA Aggressiveness' setting to 70-80% (currently on default 100%) so I may try that and also tweak the 'Min motion setting' There's a great document called 'Understanding PHD2 and getting it to work properly' that Ive been reading and it helped me set things up at the start. In there it talks about the Calibration step size, the example given for the writers set up with a pixel scale of 2.67 arc-secounds per pixel, he sets the steps to between 2000-2500ms, he states that if your pixel scale is higher then to up that amount, mine is 3.44. In PHD2 I have changed mine to 3000ms to start with but it wont allow me to change this in the advanced section settings and keeps it on the calculated '1950' for the guide scope details I have put in so not sure what to do here?

The guiding can get upset after a dither,  I have read that if the Dec cant recover well after a dither then to dither only in RA, from reading up this doesn't seem to be a good option and produces 'walking noise'

I want to clarify in PHD2, what is the 'Guide speed n.nn x sidereal'? is, is that the Guide rate? Mine is on 0.5, it also states in the document to set that to 1x so should I?

What are the readings to keep an eye on, in real simple terms? My graph can look crazy but what are readings besides the TOT that I need an eye on to help me tell how the guiding is really going? I believe there are some in regards to the image pixel scale?

I'm not sure how to get the logs files from my sessions so currently I only have to below cropped image for you to go by and it would be good to get that settled out. i know there's lots of factors, I have been reading but lets start with the good basics, and as you know I can struggle to understand things so I simple terms please! ☺️

To add, I know about the Guide assistance but a little worried i wont really understand it at the moment.

Edited October 13, 2020 by Rustang

[Rustang]

PHD2_GuideLog_2020-09-09_215827.txt Ive found the logs, here are a couple from my last session.

PHD2_DebugLog_2020-10-09_205113.txt

[wimvb]

1 hour ago, Rustang said:

Up until now all Ive known really is to make sure the TOT reading stays under 1 and your good!, it has been doing that fairly well, keeping between 0.4-0.8 most if the time

The guide error, RMS value you are refering to, should be the one in arcseconds, which for you is 1.53” if I read correctly. This value should be at most half your imaging scale, ie less than 1.1”, otherwise tracking errors will affect the stars in your images.

To avoid guiding on seeing flicker, keep your exposure time several seconds. If you go below 1 second, the guide star will move due to seeing.

The guide assistant will give you recommended settings. Use these as a baseline. It will also show your polar alignment error and DEC backlash. If the latter is large, keep a small polar misalignment, and guide in only one DEC direction (opposing the drift).

On the phd website, there is a link to a guiding analysis program. Download and install to analyse your guide logs.

Edited October 13, 2020 by wimvb

[wimvb]

http://adgsoftware.com/phd2utils/
for the guide log viewer

[Rustang]

40 minutes ago, wimvb said:

The guide error, RMS value you are refering to, should be the one in arcseconds, which for you is 1.53” if I read correctly. This value should be at most half your imaging scale, ie less than 1.1”, otherwise tracking errors will affect the stars in your images.

To avoid guiding on seeing flicker, keep your exposure time several seconds. If you go below 1 second, the guide star will move due to seeing.

The guide assistant will give you recommended settings. Use these as a baseline. It will also show your polar alignment error and DEC backlash. If the latter is large, keep a small polar misalignment, and guide in only one DEC direction (opposing the drift).

On the phd website, there is a link to a guiding analysis program. Download and install to analyse your guide logs.

When you say 'read correct;y' you mean from the blurry picture? By imaging scale you mean the imaging camera's Pixel scale which with my canon 600d and 600fl scope is 1.5 so as you says needs to be 1.1 or less, if its 1.53 then that's why I had star issues in my last session. Or do you mean the 3.44 Image scale of the guide scope would then need to be under 1.7 ?

When you say exposure time, you mean the number to the right of the 'stop' symbol on PHD2 which i currently have set to 2s !?

Edited October 13, 2020 by Rustang

[Seelive]

I've never quite understood why guiding accuracy is referenced to arcsec on the guiding log. I would guess that PHD2 can only guide at best to within about +/- 0.1 PIXELS of the guide camera.  What that results in +/- PIXELS on the imaging camera depends upon the focal length of the guide scope, the focal length of the imaging scope, the pixel size of the guide camera and the pixel size of the imaging camera. If you are getting round stars, then I wouldn't worry too much about the guide log, but if you're not and the guide log shows guiding errors of less than 0.2 pixels then I would suggest you need to consider your hardware setup.

[wimvb]

58 minutes ago, Rustang said:

When you say 'read correct;y' you mean from the blurry picture?

Yes

1 hour ago, Rustang said:

By imaging scale you mean the imaging camera's Pixel scale which with my canon 600d and 600fl scope is 1.5 so as you says needs to be 1.1 or less, if its 1.53 then that's why I had star issues in my last session.

Sorry, my bad. Imaging scale ir pixel scale = 4.3*206/600 = 1.6”/pixel. Guide rms should then be < 0.8”. If it’s 1.5”, it’s more than 1 pixel, and since RA rms is larger than DEC rms, you won’t have round stars.

[wimvb]

1 hour ago, Rustang said:

When you say exposure time, you mean the number to the right of the 'stop' symbol on PHD2 which i currently have set to 2s !?

Yes, I couldn’t see that in your screen shot. If you can increase that, the guiding variation may decrease.

[Rustang]

2 minutes ago, wimvb said:

Yes, I couldn’t see that in your screen shot. If you can increase that, the guiding variation may decrease.

Thanks, appreciate the help as always. I will put this together with what Ive been reading and make some small changes and go from there 👍

Edited October 13, 2020 by Rustang

[Rustang]

38 minutes ago, Seelive said:

I've never quite understood why guiding accuracy is referenced to arcsec on the guiding log. I would guess that PHD2 can only guide at best to within about +/- 0.1 PIXELS of the guide camera.  What that results in +/- PIXELS on the imaging camera depends upon the focal length of the guide scope, the focal length of the imaging scope, the pixel size of the guide camera and the pixel size of the imaging camera. If you are getting round stars, then I wouldn't worry too much about the guide log, but if you're not and the guide log shows guiding errors of less than 0.2 pixels then I would suggest you need to consider your hardware setup.

Ive never quite understood most of astrophotography let alone all this calculations stuff! 😄

[wimvb]

42 minutes ago, Seelive said:

. If you are getting round stars, then I wouldn't worry too much about the guide log

If the guide deviations are equal in ra and dec, and truly random, your stars will look fat and blurry. You really need guide rms less than half image pixel scale if you want to keep details in your images. At the same time, you can’t expect guiding to be better than 0.1 - 0.2 pixels. That’s why the guiding pixel scale shouldn’t be too large compared to the imaging pixel scale.

Edited October 13, 2020 by wimvb