What is an 'Orthonogality error'

[slim mole]

The first clear dark (ish) night and I have dusted down my 'scope with the intention of trying to get to grips with guiding. I have a sw200 pds, with an st80 as a guide scope all sitting atop an eq5.

Found a suitable star in PHD and asked it to calibrate. After a few minutes I got a warning about my RA and Dec having a suspicious calibration, a button on the warning lead me to the attached detail. 

I have no idea what it means by the Orthogonality Error, but I dont like the fact that its nearly 90 degrees adrift. From the graph it looks like my RA driver is making the same changes to my direction as the Dec, but that doesn't seem to make any sense. 

As my own sanity check I was able to find M31 using the slew buttons ok the SynScan hand set, so I think my goto is working (at least its move the telescope when I ask it too).

Any advice on what I am doing wrong would be greatly appreciated

Thanks In Addvance

Moley

[michael8554]

Most strange ! Yes it does look like the Calibration commands are both going to the same axis.

When Calibration starts, does the star image step to the left of your screen in time with the messages "step 1", "step 2" etc?

Then return to more or less the start position?

And similarly does the star image step vertically down your screen in time with the step messages?

And back to the start position?

That is the normal behaviour.

Michael

[slim mole]

Thanks for the reply Michael. I never got any star to track at all, always seemed to drift away from the cross hairs in one direction during calibration. And in normal tracking I would also  the star drifting off in the same direction. 

This was working ok on my old 50mm guide scope. I upgraded to the ST80 to help with picking a suitable star to guide on (which has significantly improved) but now I have loads of stars I can see but the tracking has gone to pot 

[Tony H]

This link may well help you understand and then correct the error:  http://www.company7.com/library/techin/orthogonality.html

[Tony H]

...and someone else here has been through the same it seems...http://stargazerslounge.com/topic/238953-phd-non-orthogonal-error/

[lensman57]

How good was your Polar alignment?

A.G

[slim mole]

How good was your Polar alignment?

A.G

Err, well, lets say I made a cursory nod in the general direction of polar aligning. I could understand if I got a few degrees of error with my setup, but not 90 (89.9).

With just Sidereal tracking on my mount I was getting a small amount of drift , but at 90 degrees to the drift I was getting when trying to set up guiding

[Pompey Monkey]

Was the "sidereal tracking rate" on in ASCOM?

If it's not on, you'll get the orthogonality error in the calibration, for sure!

Don't ask me how I know.

[kalasinman]

Any chance you've been guiding on a hot pixel? You are using a bad pixel map or dark library in PHD2?

[slim mole]

Was the "sidereal tracking rate" on in ASCOM?

If it's not on, you'll get the orthogonality error in the calibration, for sure!

Don't ask me how I know.

Without the sidereal tracking on in EQMOD I couldn't even click on a star to select it for guiding, more like little thin worms crawling across the screen ! Thanks for the post though, confirms that it needs to be on, rather than off...... something I have always assumed and never known.

[slim mole]

Any chance you've been guiding on a hot pixel? You are using a bad pixel map or dark library in PHD2?

I tried various areas of the sky and a couple of nice big stars (Vega, Deneb, Atlair) as my targets, all had the same issue.

When/If we get another clear night I think I will roll back all the changes in my setup since my last successful attempt at guiding (new PC, ST80, etc) and see if I can get it working again, then add the new stuff back in one change at a time.... see where things go Pete Tong

[michael8554]

Could you explain your reply #7, I didn't get the bit about drifting at 90 degrees etc ?

There is something fairly basic wrong with your setup, so I wouldn't bother yet with chasing Orthogonality, that's usually very fine tweaking. Here're a few more things to try:

If you GoTo a star, without PHD connected to the mount, does it remain stationary in the eyepiece? That would prove your PA is good enough for visual use at least. If it moves rapidly out of the eyepiece then your RA drive is not running, or is not at the correct speed.

With PHD connected, the RA drive on your mount should be acurate enough on its own (only the Loop Exposures button pressed) to hold the guide star fairly stationary on the screen. Stars shouldn't be streaking across the screen. 

In the Tools dropdown menu is Manual Guide. This can be used to check your connections to the mount. While looping exposures try moving North and then East  - you may have to increase the Guide Pulse Duration on the Manual Guide window to a bigger figure to get a noticeable move. Does the star move in the right directions?

Michael

[slim mole]

Could you explain your reply #7, I didn't get the bit about drifting at 90 degrees etc ?

There is something fairly basic wrong with your setup, so I wouldn't bother yet with chasing Orthogonality, that's usually very fine tweaking. Here're a few more things to try:

If you GoTo a star, without PHD connected to the mount, does it remain stationary in the eyepiece? That would prove your PA is good enough for visual use at least. If it moves rapidly out of the eyepiece then your RA drive is not running, or is not at the correct speed.

With PHD connected, the RA drive on your mount should be acurate enough on its own (only the Loop Exposures button pressed) to hold the guide star fairly stationary on the screen. Stars shouldn't be streaking across the screen. 

In the Tools dropdown menu is Manual Guide. This can be used to check your connections to the mount. While looping exposures try moving North and then East  - you may have to increase the Guide Pulse Duration on the Manual Guide window to a bigger figure to get a noticeable move. Does the star move in the right directions?

Michael

Reply #7 - Essentially when I was getting ready to pick a star to  guide on there was a slight drift east-west, but after starting to guide, the same start would then drift approximately north - south.

As I had only pointed my mount to the pole (rather than a full alignment) I was expecting some drift, but assumed that the guiding system would correct for that (my previous attempts had been carried out in the same way, and worked well)

I never got to the point of visually using the main telescope while trying to set up the guiding, so not sure how static any object would have been. If pretty sure the RA drives are working ok, as I was able to manually (ie through the synscan hand set) point the telescope at M31 and keep it there through the slew controls.

Will test your other suggestions, hopefully tonight if the weather gods (specifically the evil one that looks after clouds) smile on me !

Thanks

[kookoo_gr]

First of all you need to remove any factors that may introduce error to the calibration process. Make a precise polar alignment, alignmaster is a very good tool, alternatevely use the ccd drift alignment method. After that is out of the way press the brain icon at phd and at the tab mount parameters you will find a button that reads calculate. There place the parameters of your guide setup and press calculate, this will calculate the calibration step for your guide setup. Then calibrate

[slim mole]

Thanks for all of the advice. 

I had a good session last night and eliminated as many causes for error as I could (good Polar alignment, nice collection of suitable stars). I rolled back all the changes I had made to my system over the past few months and checked guiding. Still getting the same problem, the guide software was unable to make any changes to the RA on my mount. The handset and EQMOD both RA and DEC, so assuming that the issue is in pulse only.  So with little else I could do I sat in the garden with a few beers and watched the Perseids. 

It was only this morning that I realised my guide camera has an ST4 port, so I could have tried that to see if the issue is with the mount or the hand set ..... Doh !

[slim mole]

Finally at home and a cloudless (ish) night, so had another stab at guiding.

Replaced the hand controller with an HiTec Astro EQDIR, and put in an ST4 cable. Found a suitable star and within a few minutes, I was guiding.... sort of. 

The star was essentially circling the cross hairs, but after 30 minutes the telescope was still guiding (previously it would have lost the star in about a minute), so progress.

This was with a 9x50 finder, so decided to move the guide camera to my St80. The thinking being that with better light capturing I would decrease the update rate on PHD and maybe get more adjustments per second......

Unfortunately, by the time I got everything set up, the sky had clouded up (it took me 5 minutes to notice as I assumed something was up with PHD as I was getting very low signal to noise rations, should have just looked up !) 

Will try the ST80 again on the next cloudless night

[glowingturnip]

 (it took me 5 minutes to notice as I assumed something was up with PHD as I was getting very low signal to noise rations, should have just looked up !)

been there done that !