PHD Calibration

[martin_h]

Sometimes PHD won't calibrate N/S. It will do E/W in about 14 steps but refuses to do N/S even tho I have the step size set to 1600.

I have found a way to kick start it into action - change the step size by 1 unit, it doesnt matter which way, up or down.

It did it just now and got to 40 steps before I abandoned it, changed the step size by 1 unit and it did it in 12 steps.....I dont know why but it seems to work for me.

[mark7331]

Martin, I just wondered how smooth was the guiding after you got it calibrated? When I can't get it to do N/S I just pick another star but this could be a time saver if the guiding is good.

Cheers

Mark

[martin_h]

My Dec is nearly a flat line, RA is so,so depending on the seeing, so in all fairly smooth. I find that it just needs a kickstart. I was imaging a cluster so all the stars in the PHD screen were much the same, Ive used this method a few times now and it always seems to do the trick.

[mark7331]

Great. I'll give it a try when it happens next.

[carastro]

This looks like the sort of thread I have been hoping for. I have been having problems calibrating in DEC (PHD). Once I can get past calibration guiding works fine.

What do you mean by 1 unit though?

These are my current settings, but from what I have read looks like I need to up the calibration steps, but I don't understand what you mean by 1 unit. 501 instead of 500?

thanks

Carole

[Uranium235]

Carole, youre using the CG5-GT? Im using the same mount and PHD always has a problem doing the S calibration. The N works fine, but the S only moves the star a couple of pixels before kicking into guiding mode. Most of the time I stop guiding, re-select the guide star and carry on, though that mostly depends on how good my PA is that evening .... still get backlash though - even though my setup is under 4kg.

Daft question, but is the N/S calibration in PHD related to RA or DEC? Its not something that ive had time to look into while rushing to take advantage of rare clear skies.

Your calibration step size depends on the FL of your guidescope, for an ST80 I used 800-1100 and for the 50mm finderguider I use 1600-1800. Your current setting (500) seems a bit short.

[martin_h]

This looks like the sort of thread I have been hoping for. I have been having problems calibrating in DEC (PHD). Once I can get past calibration guiding works fine.

What do you mean by 1 unit though?

These are my current settings, but from what I have read looks like I need to up the calibration steps, but I don't understand what you mean by 1 unit. 501 instead of 500?

thanks

Carole

I would up the calibration steps on yours to about 1000 and try that first, and yes 1 unit would make it 1001 or 999, I dont know why but it seems to work for me.

[carastro]

Thanks Guys, was getting to the end of my tether as I tried swapping all the hardware, guidecamera, cables, laptop and even mount (I have one CG5 GT on a pier and one I use for Sky camp).

I have also E mailed Craig Stark at Stark labs and it seems like failure in DEC is a known problem. This is a quote from the problems page:

QUOTE" Does RA calibrate just fine but not DEC? PHD tries to clear out the

> backlash in DEC before calibrating, but it may not succeed if there is a lot

> of it. Have PHD running in the loop mode, you can see how long it takes to

> take up the DEC backlash using your mount’s normal controller. Go N until

> you move, then switch to S and count how many seconds it takes. PHD tries to

> take up the DEC backlash before calibration but if there’s a lot and/or the

> calibration step size is too short, it may not work. To get around this, you

> can manually take out the backlash prior to calibration. N is calibrated

> first. Figure out the arrow on your handbox that does the same motion as

> this. Before entering the calibration, hit this until the star starts to

> move. Then calibrate and you should get the DEC done just fine" UNQUOTE

Meanwhile I'll try upping the calibration step to 1000 (when we get some clear skies ).

Carole

[martin_h]

Ah Ha! that explains it - I'd forgotten about the Dec backlash, so my method isnt doing anything realy.....The first time round its taking some of the backlash but failing, so by stopping the calibration then re-starting its able to take the rest of the backlash the second time round.

[Uranium235]

I been digging and I came across these threads:

Telescope Reviews: PHD guiding failure with SSAG Orion guider package

CN FORUMS ARCHIVE Telescope Reviews: PHD Guiding problem

Both of them contain info from Craig Stark in regard to Minimum motion, step sizes and DEC calibration. From what is said there you can figure out what you need for your setup. There are some truly handy hints... and they work! My dec graph is as flat as a pancake right now

here's the proof:

[old_eyes]

Wow! I dream pf guide curves like that! I have it working 'OK' but haven't figured out which bits of tweaking are needed, and timeunder a clear sky is precious.

old_eyes

[Amazing]

How does the PHD software work, I was just looking into that, I got this CCD

Philips SPC900N, with that software does the webcam hook up to like a laptop and this software helps to track the stars?

[carastro]

How does the PHD software work, I was just looking into that, I got this CCD Philips SPC900N, with that software does the webcam hook up to like a laptop and this software helps to track the stars?

Yes so long as your webcam sees stars you can use it as a guide camera, but you will need guide cables and a guiding telescope as well and some means of fitting the guidescope to your mount so it's looking in the same direction as your imaging scope. (apologies if you already knew that).

Carole

[carastro]

Follow up to my earlier posts:

Your calibration step size depends on the FL of your guidescope, for an ST80 I used 800-1100 and for the 50mm finderguider I use 1600-1800. Your current setting (500) seems a bit short.

Went out two nights ago and tried to calibrate on same settings = DEC CALIBRATION FAILURE

Upped the Calibrations steps to 1200 and it calibrated straight away, however the guiding was not as good as usual ("usual" being once it gets past the failed calibration stage). So will reduce the calibration to 1000 next time I go out and see what happens.

Carole

[msinclairinork]

I been digging and I came across these threads:

Telescope Reviews: PHD guiding failure with SSAG Orion guider package

CN FORUMS ARCHIVE Telescope Reviews: PHD Guiding problem

Both of them contain info from Craig Stark in regard to Minimum motion, step sizes and DEC calibration. From what is said there you can figure out what you need for your setup. There are some truly handy hints... and they work! My dec graph is as flat as a pancake right now

here's the proof:

wow my head really hurts after reading all that!

But seriously thanks for posting that up, I may have only absorbed <50% but atleast I feel a bit more prepared should any problems arise in the future

Cheers,

Michael

[RobH]

I ran into the DEC calibration problem when I first started using it, but once I'd read about the DEC backlash issue, I just nudged the mount to the north before starting calibration, and never had the problem again.

Rob

[carastro]

nudged the mount to the north before starting calibration

This is what Craig Stark says, and this is how I interpret what he says. Rob would you be kind enough to tell me if I have got this right and if not what I should be doing.

I am assuming you let it go through the E & W calibration steps, then while it is checking backlash I use the handset and move the mount N a few pixels. This should be completed before it starts calibration N & S.

Thanks

Carole

[RobH]

No, don't interfere with the mount position once calibration has started or it'll all go pear shaped!!

Using the hand controller, nudge the mount a couple of pixels to the north before you start the calibration routine.

That will take up all of the DEC backlash.....you'll notice this once the mount has finished it's E/W calibration as when it gets to the 'clearing DEC backlash' stage, this will be done super quick.

Cheers

Rob

[MikeWilson]

Nice thread! I had this issue a couple of nights ago.

I'll remember the 'nudge the mount north' trick and take a look at increasing the calibration steps.

Thanks again.

Mike

[mark webster]

This sounds like the problem I'm having as it says not enough movement in dec so turning off dec then it starts guiding. Now I know this might sound stupid but when you say nudge north do you mean up wards towards the Polaris or as in compass north east and west. Don't laugh I'm only a novice

[carastro]

Yes towards polaris, you need to work out which way your handset arrows will take you.

BTW I upped my calibration setps to 1000 - 1500 as suggested by Craig Stark and calibration worked from then onwards.

Phew!!

Carole

[mark webster]

Thanks for that I'm having so much trouble . I have my calibration steps set to 2500.

I will give it a go again when we get a clear night. Keeping my fingers crossed this will work

[carastro]

Mark, I learnt a lot when I had guiding problems. They say the mount should be weighted to the East. i.e. If you're imaging on the east side, the weights should be heavier. If you're imaging to the west the weights should be lighter. Never did find out what happens if you're imaging to the north or south though, although it's bound to be slightly to one side or another.

Also, make sure you don't have any shift (flexure) in the drawtube of the guidescope (or the imaging scope for that matter), make sure there is no drag on cables (tie them up so any drag will not be on the cameras.

Carole

[swag72]

Carole, can you just confirm about the weights? Do you mean that if my weights are facing towards East they should be heavier and if the weights face westwards then lighter? Does this mean East / West as per a compass, or is there someother East / West with imaging?

[mark webster]

After all of this I've found my problem the ST4 cable that came with the camera is faulty. By pressing Ctrl & T when in PHD it will send test pulses to the mount and mine did not respond at all in the N Dec and E RA modes. Checked the cable for continuity with a multi-meter and found 2 wires faulty

Tried the test via the handset using Ascom and doing away with the ST4 cable and all 4 directions work. I've spent months trying to sort this out