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PHD Dec all over the shop!

Spoon

By Spoon
in Discussions - Software

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Spoon

Spoon

Posted
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afternoon,

its supposed to be clear here tonight so thought i would go if out if it is. Thing is, the last 4/5 times if guided the dec goes off the chart within a minute. What causes this and how can i prevent it?

Thanks,

Cam

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Spoon

Spoon

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Hi Cam, really new to guiding but the thing that springs to mind is ota balance ...

has it been ok before but now playing up or always done it ?

i try and do everything as best  can when setting up but OTA balance is the one thing i do lightly, i do it well enough so it balances but not really accurately.

When i first started guiding, i think the second night i was getting 10min subs without ANY errors, no trails nothing.

Will  do everything properly tonight and let you know

Cam

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Spoon

Spoon

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Is DEC guiding disabled ?

If so your PA is out.

No i'm pretty sure its enabled. How do you check?

PA is the thing i do as best i can as i know it is very important. My routine may be wrong though :/ i used AstronomyShed on youtube's tutorial i think?

Cam

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wxsatuser

wxsatuser

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No i'm pretty sure its enabled. How do you check?

PA is the thing i do as best i can as i know it is very important. My routine may be wrong though :/ i used AstronomyShed on youtube's tutorial i think?

Cam

I think it is auto as default,

Check in brain, top right, dec guide mode....... I'm using old version btw.

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ChrisLX200

ChrisLX200

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The first thing I would try (mainly because it's quick and easy) is to uninstall and re-install PHD!  Why? Because I had this very issue with the DEC running away and I spent quite some time head-scratching trying to find the reason. A re-install was one of the last things I tried and it was an instant fix for the problem. Not saying it will sort yours out but it's worth a try.

ChrisH

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Spoon

Spoon

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My guiding used to do the same thing when imaging anything near the meridian, I found that balancing the scope well made it rock on the gears, so made the mount scope heavy and it cured the problem for me.

This is when I'm imaging the Cygnus area though so quite a bit away from the meridian.

I think it is auto as default,

Check in brain, top right, dec guide mode....... I'm using old version btw.

Yep it's on auto. I hadn't changed anything so should have been on anyway.

The first thing I would try (mainly because it's quick and easy) is to uninstall and re-install PHD! Why? Because I had this very issue with the DEC running away and I spent quite some time head-scratching trying to find the reason. A re-install was one of the last things I tried and it was an instant fix for the problem. Not saying it will sort yours out but it's worth a try.

ChrisH

Hmm ok will try it when I get home. Will let you know if I lt works.

Cheers,

Cam

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wxsatuser

wxsatuser

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I would do a DARV and check your PA.

Plus don't perfectly balance your setup, make it a bit heavy east side so it keeps the gears meshed.

If you cross the meridian then the unbalance wants to be the other way.

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Spoon

Spoon

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I would do a DARV and check your PA.

Plus don't perfectly balance your setup, make it a bit heavy east side so it keeps the gears meshed.

If you cross the meridian then the unbalance wants to be the other way.

What is a DARV?

I will try east heavy next time I go out :)

Cam

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wxsatuser

wxsatuser

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I dd try Alignmaster but I could never quite get it spot on, others have but me no. :grin:

DARV is time consuming for a non permanent setup but if you have an obsy it's the dogs.

There is another way, drift align with PHD, with this you can see immediate results.

For azimuth.

Calibrate and guide on a star near the meridian and zero degrees DEC.

Open the graph and change to DX/DY, it's normally RA/DEC.

Turn off DEC guiding.

The red line, if your PA is spot on, will be a straight line near the centre.

If PA is out the redline will drift up or down.

If it drifts, carefully adjust your azimuth bolts to bring the redline back to the centre.

For elevation

Calibrate and guide on a star towards the east or west and at zero degrees DEC.

Use graph as before.

Turn off DEC guiding.

Again if your PA is out the red line will drift but this time use the elevation bolts to get

it back to the centreline.

Try a few iterations as moving one may affect the other.

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wxsatuser

wxsatuser

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I can find how to turn off dec guiding?

You can turn off DEC guiding in the graph.

Bottom right of graph there is a dropdown box, it should be auto.

Click it and set to off.

BTW I'm using the old version, not PHD2.

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Christopher Davenport

Christopher Davenport

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I dd try Alignmaster but I could never quite get it spot on, others have but me no. :grin:

DARV is time consuming for a non permanent setup but if you have an obsy it's the dogs.

There is another way, drift align with PHD, with this you can see immediate results.

For azimuth.

Calibrate and guide on a star near the meridian and zero degrees DEC.

Open the graph and change to DX/DY, it's normally RA/DEC.

Turn off DEC guiding.

The red line, if your PA is spot on, will be a straight line near the centre.

If PA is out the redline will drift up or down.

If it drifts, carefully adjust your azimuth bolts to bring the redline back to the centre.

For elevation

Calibrate and guide on a star towards the east or west and at zero degrees DEC.

Use graph as before.

Turn off DEC guiding.

Again if your PA is out the red line will drift but this time use the elevation bolts to get

it back to the centreline.

Try a few iterations as moving one may affect the other.

Thanks for this, new method for polar align, I normally drift align with APT using zoom as the movement is quick to pickup.

Your method sounds way more scientific, I will give it a go next time I am out.

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wxsatuser

wxsatuser

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It's a method I have seen in various places and tried it, the effect is immediate as you turn the bolts.

At first I was over compensating, a light touch is needed but once mastered it is easy to get that red line straight.

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IanL

IanL

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If you're getting serious drift in Dec in just one direction, it won't be due to scope / counterweight balance issues.

Balance issues will normally result in erratic guiding with the trace shooting up and down the graph wildly.  Unhelpfully it can be so severe that is might look like drift in one direction if the trace shoots rapidly off the graph never to return, so you may need to change the graph scale or check your logs to be sure (e.g. load them in to PHDLab or similar).  Balance problems normally become more severe as you get close to the meridian (in RA) or the zenith (in Dec).

(For the record,unbalancing by moving the weights deals with problems in RA.  Any unbalancing needed for Dec would be achieved by moving the scope backwards/forwards in the rings or the dovetail in the clamp).

I would check:

- Is everything mechanically sound - covered in detail in the guide linked in a previous post, but even a small amount of slop in the mechanicals can throw things off (check the mount, clutches, scope/guider mounting, focuser, camera, cables dragging on things, etc.)

- Whether the Dec guiding commands are being acted on - again the tests are detailed in the guide.

- Did you get a successful calibration before guiding - if PHD is calibrating in a few steps it may be inaccurate and so you may need to modify the calibration step size.

- Polar alignment - a poor polar alignment might cause so much drift that the guiding cannot keep up with it, but equally a perfect polar alignment will cause PHD to want to switch guiding directions in Dec frequently, which in turn may lead to erratic guiding due to backlash in the gears. (If you think you have nailed PA, then you can try turning off Dec guiding but this would only usually be viable with a permanent mount set-up).  A slight misalignment is ideal, just enough so that Dec guiding only corrects for drift in one direction.  Just enough so that seeing effects don't cause PHD to reverse direction, but not so much that field rotation becomes an issue (at long focal lengths normally).

- PHD settings - the main settings to fiddle with are described at the end of the guide; if everything else is good then it might be that the guide commands are being limited too much to keep up with the drift.  You might also want to look at the guiding rate you are using (set by the hand controller or EQMOD).  Maybe try a slightly higher guide rate, but remember to re-calibrate each time you change it.

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Spoon

Spoon

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It's a method I have seen in various places and tried it, the effect is immediate as you turn the bolts.

At first I was over compensating, a light touch is needed but once mastered it is easy to get that red line straight.

When I did that there was still two lines even though one was off?

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