PHD help - edit calibration? Dec Backlash?

[rogerg]

G'day all,

I'm fairly new at using PHD since it's not really worked for me in the past, until very recently when it's showing some good signs of working.

I'm having a little trouble with Calibration at the moment. :help: My FOV is very wide so large movements are required to show mount direction. My GM8 also have significant backlash. My polar alignment is average. These 3 factors seem to be confusing it.

It seems to not be waiting long enough to do Dec backlash and then seems to only attempt to remove dec backlash in one direction (the first dec direction it tries, north I think).

I can't find a setting to tell it how much dec backlash to soak up before trying to calibrate?

Once calibrated it has RA quite nice but Dec is way off, it shoots off, presumably due to incorrect calibration. If I were in CCDSoft I would solve the problem by editing the calibration settings for Dec to values I know are reasonable.

I can't find access to the calibration settings PHD generates. Is it possible to manually edit the calibration?

Thanks for any assistance :thumbsup:,

Roger.

[gbeal]

Roger,
I too struggle with understanding PHD, mind you I don't have a PHD either, LOL.
You have tried the "Brain" symbol? This allows you to modify the parameters etc, although I am not sure about the calibration.
Gary

[aworley]

Hi Roger,

I would suggest that you put a bit of effort into polar alignment and see how you go....I use the CCD Drift method (takes about 5 minutes to get close enough for PHD to do the rest).....

here's one link to ccd drift method....I use 30 or 60 secs depending...

http://www.deepskyjam.com/Files_GB/TechNote/DriftCCD/CCD_Drift_Method_02.asp

PHD only removes backlash in one direction for me (can't remember which way, I think after west???) I use mostly the default settings although give calibration steps a good shunt near the poles - but it sounds like you have got that bit licked anyhow...

Alex

[JohnG]

Hi Roger

These are the setting I use for my GM-8 mount with an 800mm f/l telescope:

In the "Brain" symbol

RA Aggressiveness: 75
RA Hysteresis: 10
Dec Guide Mode: Auto
Dec Algorithm: Resist Switching
Calibration Steps: (ms) 600

The Calibration Steps can be highlighted and a new number typed in, I have used 1000 ms without any problems.

The remainder of the values I leave at default.

A reasonable Polar Align is needed, other than that, it works just fine for me using a Q-Guider as an autoguider.

Cheers

[rogerg]

Thanks all,

I've played around in the "brain" a bit... I actually have the calibration steps set at 3000! Focal length is 700mm, using Q-Guider.

I can't remember the values for the other settings, they'd be the defaults.

Sounds like I need to stop trying to fix the calibration problem and just pay attention to my polar alignment... exactly what I'd be telling someone else in my situation :lol: ahh gez I hate having to spend time on that :) .. sure, it's not long, but you know. I guess with Guide Dog I got used to being able to just let it counter act the polar error when I was lazy.

OK, will do more work on my polar alignment tonight and try again.

Oh, that Dec "Resist Switching" sounds good too, thanks for that.. I will try that one, sounds like what I need in some situations, as Dec only needs to be corrected in one direction in theory for me.

Roger.

[leon]

I have to agree with the comments on having your set up, at least pretty well polar aligned.

I use, and love PHD, rarely I change any default settings, and it never lets me down.

It is the foundation work that makes it all happen.

Leon

[seeker372011]

the calibration step you are using 3000 seems waaay too high

I have a 900 mm guidescope, and 1000 when guiding near the pole and 500 when far away seem to work well
The trick is to get around 20 to 30 calibration steps I find in NS and EW respectively. More than 60 steps, PHD will give up; less than 10 simply doesn't work !
usually dec backlash is cleared in around 6 steps or less..probably mount dependent

I think PHD will guide even if your polar alignment isn't all that flash; your resultant image may have filed rotation of course. But for guiding it doesn't have to be that perfect

[rogerg]

interesting... I was finding that numbers less than 2000 were just not moving the star very far, but perhaps I'm thinking the wrong with when it comes to PHD.

With CCDSoft (what I'm used to) your aim is in the one movement to move the star a good distance across the screen such that CCDSoft can re-analise the whole FOV, detect where the star has moved to and then have a good number of pixels in movement to get a reasonable vector. I'm now realising the contrast between that and PHD's method where it follows the star bit by bit for x steps.

I'll see if I can get that majical 30 or so steps :thumbsup: .. I think that will be a value of about 1500 for me.

Thanks,
Roger.

[leon]

Roger are you telling me that it takes more than 30 steps to calibrate, for me if i image to the SCP it takes about 25, but anywhere else t is not more than 15-20, this is what you need to achieve

Leon

[danielsun]

Roger, provided you have PHD version 1.9.0 or newer there is a very handy feature, once you get your polar alignment close enough click on tools and select enable graph and this will tell you how well your mount is guiding.

Cheers Daniel.

[PeterO]

It also helps to not do a calibration near the pole or on the meridian.

[rogerg]

G'day all,

Thanks for your replies. I have it working now. Steps to success:

1) improved polar alignment quite dramatically
2) set calibration steps to 1000

Seesm to have been guiding OK for about 2 hours solidnow. :thumbsup:

[gbeal]

I thought you needed to calibrate close to where you were actually imaging?
You are saying calibrate in one area, and image in another?
Gary

[seeker372011]

not a good idea methinks; usually its best to recalibrate every time you slew to a new target a reasonable distance away -and especially if a meridian flip is involved it goes without saying

[PeterO]

I've never had a problem with only doing one cal per side for exposures up to 10 min, my mount is permanent and very well aligned though. Yes need to recal on a meridian flip.

[rogerg]

I believe it is best to calibrate near your target, but it's definitely not required. On my LX200 using CCDSoft I calibrate once every couple of months, and image targets ll over te sky. With PHD I plan to do it near the targets until I work out how well it performs.

Roger.