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Old 21-02-2008, 10:54 AM
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pvelez (Pete)
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PHD settings

I'm having a play with PHD as my guiding has not been crash-hot to date and would appreciate any tips from the gurus.

I have set Dec guiding to off. My research suggests that this results in guiding to address PE issues only and that I need to turn on Dec guiding as well as it is Dec guiding not RA guiding that corrects for a dodgy polar alignment. (Need I add that my polar alignment has been reasonably dodgy to date?).

If so, I switch Dec guiding to Auto.

Also, does anyone have any thoughts on the influence of a backlash % setting on PHD guiding? I read an interesting note somewhere suggesting that backlash should be set as low as possible to avoid the mount swinging back and forth too much.

I'm using an LXD75 mount with a laptop - no dedicated guide port unfortunately.

Lastly, is there a guide rate setting in Autostar? I can't find it but I have read that this needs to be set at 100%.

Thanks in advance

Pete
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Old 21-02-2008, 11:15 AM
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iceman (Mike)
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Hi Pete
I use PHD, but I've only ever used it on full auto for all the settings.

I literally plug it in, click on the camera, click on the mount, and hit go.

I only have problems losing the guidestar if it's too faint. I usually try and keep the exposure as short as possible (0.05, 0.1 or 0.2 secs), because i'm not usually polar aligned well enough to trust any longer than that
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Old 21-02-2008, 11:25 AM
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pvelez (Pete)
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Thanks Mike - I wish it was so easy for me. But I suspect its pilot error

Dunno why I've always used the Dec guiding set at Off.

Have found the FAQ on Craig Stark's site which is really useful - it answers my backlash setting question

http://www.stark-labs.com/wiki/doku....orials:phd:faq

Pete
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Old 21-02-2008, 02:16 PM
DeanoNZL (Adrian)
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Hi All.
Pete,
Not a Guru yet!
There is a driver for the Meade Mounts that has been modified to enable "Pulse Guiding" on the Stark-Labs website.
http://www.stark-labs.com/phdguiding.html
1/2 way down the page.
Reports are that this makes the LXD more responsive.
I had to increase my "Calibration Step" setting to between 950-1200 ish for a smaller scope.
What software version of Autostar are you using?
Let me know if you need anything else.
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Old 21-02-2008, 03:39 PM
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Thanks Adrian

I tried to add the revised Meade Ascom driver last night - couldn't get it to work but it was late and too cloudy to give a whirl so I left it for this evening.

I'm not sure what the Autostar software version I'm using. I think I updated about 3 months back so I guess its reasonably up to date.

I'll have another crack at it this evening with the new driver and will let you know how it goes

Pete
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Old 21-02-2008, 04:07 PM
DeanoNZL (Adrian)
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Pete,
Also, when calibrating PHD, how long does the "clearing DEC Backlash" indication last?
This was an indication of how much play there was in the DEC axis.
It may be able to be tuned slightly.
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Old 21-02-2008, 05:22 PM
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Quote:
Originally Posted by iceman View Post
Hi Pete
I use PHD, but I've only ever used it on full auto for all the settings.

I literally plug it in, click on the camera, click on the mount, and hit go.

I only have problems losing the guidestar if it's too faint. I usually try and keep the exposure as short as possible (0.05, 0.1 or 0.2 secs), because i'm not usually polar aligned well enough to trust any longer than that
Mike, wow that is short - the advice I have had is use the longest exposure you can to avaoid chasing the seeing (ie correcting for errors that are not real). The max exposure will depend on the quality of the mount (ie the max PE and how smooth it is). Normal range seems to be 2-5 secs but this will also depend on the arcsec per pixel of your imaging train. I guess Mike that your tolerance for errros is tiny due to the extreme fl and small chip sizes you are used to when doing planetary work?
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Old 21-02-2008, 05:28 PM
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Quote:
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Mike, wow that is short - the advice I have had is use the longest exposure you can to avaoid chasing the seeing (ie correcting for errors that are not real). The max exposure will depend on the quality of the mount (ie the max PE and how smooth it is). Normal range seems to be 2-5 secs but this will also depend on the arcsec per pixel of your imaging train. I guess Mike that your tolerance for errros is tiny due to the extreme fl and small chip sizes you are used to when doing planetary work?
I usually go for 2 sec, but have on occasion gone to 10 sec if the guide star is faint. Seems to work OK.
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Old 21-02-2008, 05:31 PM
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Quote:
Originally Posted by DeanoNZL View Post
Pete,
Also, when calibrating PHD, how long does the "clearing DEC Backlash" indication last?
This was an indication of how much play there was in the DEC axis.
It may be able to be tuned slightly.
Adrian, I can't honestly say. I haven't had PHD set for Dec guiding which explains why the guide don't guide very well. Will give it a go tonight (I hope - its looking cloudy again in Sydney)

Pete
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Old 21-02-2008, 06:58 PM
Alchemy (Clive)
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ive used phd and found it to be a great program, the settings i use depend to some degree on the amount of wind as my scope blows around a bit if its windy,

before i go too far i am using a losmandy G11 which is reasonably accurate,

i use a guide rate of .5 sidereal where possible and about 60% aggressive , i feel its better to catch up over 2 pulses rather than overshoot and do the left/right/left/ right thing. i use 1 second increments as i agree about chasing the seeing at a fast rate. all other settings are standard. ive experimented a bit with it and currently its the best for me.

select a star that is well defined but not FAT for the time length you use- its easier for a centroid on a small star than a big one.

if the winds up a bit i may go to 2x with maybee a 25% rate

you may as well use corrections in both axis as perfect polar alignment takes a while and one bump and its off (i have mine in a permanent ob so its set to go and aligned 24/7) i still use corrections in both axis

hope this helps some.
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Old 21-02-2008, 09:12 PM
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Righto, now I'm even more confused....Craig Stark's site recommends replacing the usual Meade ASCOM drivers with a modified version on his site.

But the ASCOM siteb then explains that you can't just cut and paste drivers.

The Stark Labs site also refers to version 4 - downloading the lates I find its version 5.

Any tips?

Pete
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Old 22-02-2008, 10:16 PM
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OK, so I've identified my problem - PHD won't calibrate in DEC only RA. The word seems to be that there s too much backlash of my mount won't move enough in dec to get it calibrated. Now all I need to do is fix it.

The manual method of taking up the backlash before calibrating doesn't seem to work.

Has anyone else ever had this problem? Or am I on my own with this??

Am getting frustrated - if PHD is foolproof then I'd like to see a definition of a fool.

Pete
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Old 22-02-2008, 11:14 PM
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One Definition of a fool.
"'Tis better to be thought a fool, than to open your mouth and remove all doubt"

Theo
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Old 23-02-2008, 07:22 AM
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Quote:
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One Definition of a fool.
"'Tis better to be thought a fool, than to open your mouth and remove all doubt"

Theo
I prefer:

"Nothing is foolproof as fools can be very ingenious"

Pete
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Old 23-02-2008, 07:36 AM
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But I still can't calibrate for declination with PHD which means no autoguiding to fix my lousy polar alignment.

Surely someone else has this problem...

Pete
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Old 23-02-2008, 11:37 PM
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I think I may have a similar problem with my Nexstar 11 GPS.

My problem now is that something is wrong with my DEC motor. If I press up, then up, up, up... it has no problems. Nice and smooth. If I then press down, the star does a big jump and usually goes off the screen.

If I then press down, down, down...again, no probs. But when I press up, big jump again.

Left and right on the RA drive is no worries at all.

PHD is working brilliantly until it tries to calibrate the DEC motor.

I think my only option is to take the side off the fork mount tomorrow, expose the gear and the worm drive, and have a go at adjusting it until I get rid of this sloppy backlash.

I will let you know how I go.

Baz.
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Old 25-02-2008, 08:21 AM
ozstockman (Mike)
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Originally Posted by pvelez View Post
But I still can't calibrate for declination with PHD which means no autoguiding to fix my lousy polar alignment.

Surely someone else has this problem...

Pete
Hi Pete,

For my understanding of calibration process it has nothing to do with bad polar alignment. It deals only with a camera position in relation to DEC and RA axes.

With GuideDog you have to rotate a camera manually to calibrate it while in PHD it's an automatic process. During calibration process it calculates the angle between RA and DEC axes and a real position of a camera sensor. When it's done PHD takes this angle into account during autoguiding. Also there is no point in doing calibration for both DEC and RA as they are always 90 degrees to each other. It means that even movement in one direction(left, right, up or down) should be enough to calibrate a camera position.

if your scope isn't aligned properly or suffers from PEs it should be compensated by autoguiding itself.

cheers,


Michael

Last edited by ozstockman; 25-02-2008 at 08:36 AM.
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Old 25-02-2008, 10:19 AM
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I believe calibration also determins the (arc sec moved / sec of correction) for each axis so thast the code can calculate the duration as well as the direction of the corrections to be applied. As you can set the guide speeds differently for each axis I think both axes need to be calibrated. Additionally if backlash correction is to be attempted then calibration in both directions are required.

Just how big is your DEC backlash? At 1x siderial how long does it take to reverse the direction a star is moving in DEC? PHD should be able to handle large DEC backlash provided you correct in one direction only (opposite any remaining drift), that works for me and my mount had 8-12 secs DEC backlash before adjustment.





I
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Old 25-02-2008, 12:13 PM
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Thanks for all your suggestions. I am pleased to report that I was able to guide in both RA and Dec on the weekend - a first for me.

From what I can tell, PHD tries to calibrate in both RA and Dec - if for some reason it can't calibrate in Dec, it turns off the Dec guiding which explains why my guided photos looked lousy over about 120 seconds.

Steps I took to sort it included:

1. I adjusted the balance on my OTA

2. I dumped version 5.1 ASCOM and re-installed version 4.1. I then replaced the Meade driver with the modified driver on Craig Stark's site. This enables pulse guiding

3. I removed the backlash adjustment from my Autostar - it was set at 10% so I took it down to zero.

4. I manually took up the backlash in 1 direction (north I believe) before calibrating.

Still no joy

Then the clincher - I increased the pulse setting for calibration from 250ms (the default I think) to 1000ms. Hey presto, it calibrates in Dec and I'm off.

Of course the clouds then came in but I had time to shoot off a 5 minute shot of Orion at ISO 100. This is quite a breakthrough for me and I'm pleased as punch - to do this and finally get a handle on drift alignment in the space of a month leaves me feeling quite chuffed.

Here's the Orion shot. It suffers from coma as the OTA is a Schmidt Newtonian (MPCC is on back order), the colimation is a bit out and the camera doesn'sit quite square on the focal plane as I need to have the Tring sitting a bit out from the extension tube to bring it to focus - hopefully the MPCC will deal with this too.

Having said all that, I think this a good shot at more than twice the exposure I have been able to achieve before.

Pete
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Old 25-02-2008, 12:15 PM
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This time with the image!

Pete
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