Please check For Guiding Error Or Backfocus distance Error.

[Singlin]

I bolted my ST 80 directly on to a vixen bar on the top of my scope rings.

Here is a link to the test images using the ST80 as a guide scope with the QHY2.

https://www.dropbox.com/s/92ei4r4yr3yzbpl/CCD%20Captured.zip?dl=0

[ollypenrice]

I bolted my ST 80 directly on to a vixen bar on the top of my scope rings.

Here is a link to the test images using the ST80 as a guide scope with the QHY2.

https://www.dropbox.com/s/92ei4r4yr3yzbpl/CCD%20Captured.zip?dl=0

That looks better. In the 900 there is a very slight elongation of the stars top to bottom but it isn't at all bad. Does the guide trace agree with this?

How do yu feel about it?

Olly

[Singlin]

My guide trace did not look good at all.

I have now installed my Aluminum plate on the inside of my focuser tube and look forward to see the difference.

[Singlin]

Having another run this evening.

Below is my guide graph.

[Singlin]

Here is the link to three fits files of this evenings session after I had installed the reinforcing plate.

https://www.dropbox.com/s/sm6l44hql8s3ng5/test%20after%20inserting%20plate.zip?dl=0

[ollypenrice]

I must say we get a far better guide trace than that from our Mesu. In Dec you are drifting to two pixels, if I read the graph correctly (not being up on PHD.) Below is a typical Astro Art/ST80/Lodestar guide trace for ours but the guide cam is running in Bin 2 so you have to double the error seen here to compare with yours if you are running unbinned. Whatever the details of pixel scale, the difference between the traces is far too extreme to ignore.

I suspect that your problem will lie in the parameters used in PHD. Min and Max movement could be the key ones but I know very little about tuning PHD. We use the Stellarcat Mesu, not the SiTech, so I don't know what guide speed options you have but we guide on our slowest guide speed in four second subs.

The problem with your guide trace is that it is fairly random so the 'round star' test is not adequate. With that level of movement you will get roundish stars while still losing resolution. (When using the 14 inch with an OAG and unbinned Lodestar at 2.4 metres FL our trace was always sub pixel.)

Olly

[Singlin]

I will send Lucas an email with my guide camera specifications and a copy of the above graph in order to get advice on how to improve things.

[steppenwolf]

Whilst it is true that I only have a 509mm focal length on my Mesu 200 (with a sampling rate of 2.19 arcseconds/pixel), I get very twitchy if my guiding errors go over 0.15 pixel (0.33 arcseconds) and I start looking for a problem!

I use an OAG which could have some bearing on this although I believe that Olly uses a guidescope?

[ollypenrice]

Whilst it is true that I only have a 509mm focal length on my Mesu 200 (with a sampling rate of 2.19 arcseconds/pixel), I get very twitchy if my guiding errors go over 0.15 pixel (0.33 arcseconds) and I start looking for a problem!

I use an OAG which could have some bearing on this although I believe that Olly uses a guidescope?

He does.   An ST80 at 4OOmm FL and usually a Lodestar in Bin2. However, Yves and I remained sub pixel usng an unbinned Lodestar and OAG at 2.4 metres FL in a previous incarnation of the Mesu.

Olly

[Singlin]

So should I be getting sub pixel guiding with my Qhy5 and St80 or is my only option an Off Axis Guider?

In which case I will have to look to change my scope.

Lucas also suggested an Off axis guider.

[pietervdv]

If the scaling on your graph is correct, a 2 arcsec RMS guiding error is not acceptable for a mount like this. I usually get lower than 0.5 arc sec with my Mesu.

What guide algorithm are you using in PHD2? You should use hysteresis mode for both RA and DEC. It is important not to use the "resist switch" mode in declination.

That does not work on a friction mount (no backlash).

Set your guide exposures to 5 sec to cancel out the seeing. For a Newtonian I would also strongly advise to use an off axis guider.

You might want to check with Lucas what kind of version RA motor you have, mine had to be replaced because of poor tracking.

Hope this helps,

Good luck,

Pieter

[Singlin]

HI Pieter,

I have just checked my settigs in PHD2 and I have indeed Resist Switch set as my Declination Algorithm.

As soon as my clients stop playing cards and go to bed I will go up and try your suggested setting.

  My mount went back to Lucas for problems with the encoders and I beleive that I have the updated motors. I received the Mount last June.

Regards,

Simon

[Singlin]

I have tried guiding in PHD with the Pieters settings and came across the following problems:

West calibration would take 17 steps and then the East would count down from 7.

When nudging the star back south I always get star lost notice after 3 nudges and cannot finish mz calibration.

Below is a screanshot of mz PHD2 settings and also mz Differential settings in Sitech.

[Singlin]

When it does the final nudge south the star keep moving south out of the box.

[Singlin]

Today's workflow.

I have re-crimped my ST4 lead as it was a bit loose.

Changed my USB lead to my guide camera.

Uninstalled both PHD and PHD2 and eliminated any log files.

Re-installed PHD2.

When my clients are in the Restaurant I will go up and have another go.

[ollypenrice]

Cables do have to be right. Best of luck!

Olly

[Owmuchonomy]

I'm no way as qualified to comment as the other posters on here but I'm following this thread with much interest. Your recent graph is particularly poor in Dec. My Heq5 achieves (achieved) around 0.9" in Dec but I note you have both N and S correction set to on. I find that once PHD2 has told me which way my Dec is drifting (with the adjustment set to off) I can then just guide in one orientation, N or S. Having said all that I've just this week fitted a belt mod and set my pier up in the new Obsy. I will keep followng with interest.

[pietervdv]

Hello,

Your PHD2 setting look pretty good.

I made a screendump of my settings, you can check them below. With this I get sub pixel guiding at 950mm each time.

Another very important thing to check in the settings of the encoders in the SiTech config file:

Are the encoders configured as "Polite"? If not the mount will try to compensate any mount adjustments made during guiding.

Best regards,

Pieter

[Singlin]

Thanks Pieter!

What guide speed should I enter in PHD2?

[Singlin]

I cannot finish the calibration due to star lost message when doing the final nudge south. the star dissappears in the opposite direction of the nudge.

Later I will install my finder scope again as the guider and see how it goes.

[Singlin]

I keep getting the message "The Ra and Dec rates vary by an unexpected amount" after trying to calibrate.

[Singlin]

I went back to trying my finderscope and QHY5 combination with PHD1.

I got the error below.

My mount is now unguidable.

[Singlin]

This is the message that I am getting in PHD2

[Singlin]

Here is my PHD2 graph after finaly managing to finish a calibration without an error message.

[Singlin]

There has to be some stupid error here.

I have already changed cables, guides scopes.

I will now uninstall all ascom drivers and camera and scope drivers and start again.

Skies not looking great for tonight though.

I have also installed Astroart demo.