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Old 12-04-2015, 08:39 AM
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speach (Simon)
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And I though guiding would be simple!

And I though guiding would be simple! How wrong was I. There seems to be some thing strange happing. See the pic (this isn't the graph from PHD just one I drew) One of the traces goes completely of the graph after about 3 mins then comes back and is ok for 3-4 mins. It can happen with either plot and isn't regular in one plot then the other. I've done PEC, the scope is balanced but not too well. and I get L shaped stars.
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  #2  
Old 12-04-2015, 09:56 AM
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A couple of points about autoguiding:

1. The mount has to be polar aligned very well. Autoguiding is not a substitute for a weak polar alignment.

2. The scope has to be well balanced. Again you will get poor results with a badly balanced mount. That includes balancing it at the angle you will most likely image at. Some setups have a guide scope on top and the balance shifts with the angle. You may need a counterweight in this case or balance for the usual angle

3. No cable dragging the camera.

4. You need a fairly sensitive yet clean autoguiding camera. Lodestar is popular, I had 2 and they didn't play well with CCDsoft and are more suited to PHD or Maxim. The SBIG STi is hard to beat.

Now you can look at autoguiding.

Autoguiding through a guide scope is inferior to guiding with an off axis guider or a self guiding camera from SBIG.

The guide scope should be attached to the telescope tube not the rings of the scope so if the scope shifts slightly so does the guide scope.

When you cross the meridian the commands need to be reversed - ie reverse X box checked or do a new calibration.

Pick a medium bright star not an oversaturated too bright star and not a double star. Don't pick a star with another brighter star nearby as it can confuse the software which calculates the centre of the guide star.

Callibrate the guider (at least in CCDSoft). PHD may do this automatically. It tells the software how much of a command corrects how much of an error.

Make sure the guide camera is square to the scope and mount. Not at an angle. Some software (CCDSoft) will take an off square guide camera into account when you do the calibration but other software may not.

Chose a guide exposure long enough to get a decent brightness to the guide star and not too long so errors build up too much. I have found that varies with the mounts but as a guide better quality mounts can go longer between corrections (like 6 seconds) compared to lesser quality mounts which may need corrections more frequently like 1 second if you have a bright enough guide star.

Some guide cameras enable you to subtract a dark from the light. This is important because the software will often pick a hot pixel as the guide star and you will get odd and large errors that don't change if that is the case. SBIG STi has a shutter so it can do dark subtracts which I have found is pretty important otherwise I get the above hot pixel messing up guiding especially in warmer temperatures.

Aggressiveness is another setting. Start with 5 and see how it goes. It it takes too long to correct an error back down then increase it. If you mount and polar alignment are spot on then you can back it down.

Backlash. Some mounts have backlash and you may need to put a setting on this. I have never used this as my mounts did not seem to have significant backlash.

Min/max move. .1 min 3 secs max. Errors outside that range are ignored and no correction is issued.

What is a guide error? If you see guide errors averaging under .2 you are doing great. Over .8 and you'll see eggy stars.

If you are using PEC make sure the PEC curve is not upside down. In which case its pulling instead of pushing and it makes guiding worse. Invert the curve and see if the errors go down as they should.

Greg.
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Old 12-04-2015, 10:58 AM
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Quote:
Originally Posted by speach View Post
And I though guiding would be simple! How wrong was I. There seems to be some thing strange happing. See the pic (this isn't the graph from PHD just one I drew) One of the traces goes completely of the graph after about 3 mins then comes back and is ok for 3-4 mins. It can happen with either plot and isn't regular in one plot then the other. I've done PEC, the scope is balanced but not too well. and I get L shaped stars.

What: mount, telescope, guide camera & guide scope are you using?
Hopefully you are using an OAG.
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Old 12-04-2015, 12:04 PM
glend (Glen)
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There are some guide cameras that just don't work well with PHD - like the ASI which are high frame rate and cause PHD to hang. If your using one of those then Metaguide is the answer - ASI supported natively and so much easier to use than PHD in my experience.
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Old 12-04-2015, 12:59 PM
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There are some guide cameras that just don't work well with PHD - like the ASI which are high frame rate and cause PHD to hang. If your using one of those then Metaguide is the answer - ASI supported natively and so much easier to use than PHD in my experience.
My ASI120MM works fine with PHD2. PHD2 has native and ASCOM support for this camera.
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Old 12-04-2015, 01:29 PM
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Amaranthus (Barry)
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ASI120MM works fantastically with PHD2 using the ZWO ASCOM driver.
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Old 13-04-2015, 10:37 AM
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Shiraz (Ray)
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Quote:
Originally Posted by speach View Post
And I though guiding would be simple! How wrong was I. There seems to be some thing strange happing. See the pic (this isn't the graph from PHD just one I drew) One of the traces goes completely of the graph after about 3 mins then comes back and is ok for 3-4 mins. It can happen with either plot and isn't regular in one plot then the other. I've done PEC, the scope is balanced but not too well. and I get L shaped stars.
It would help a lot if you could put up an image of your parameter settings - for example, it might possibly be that you have maximum move or correction rate set too low.

also would probably help to know what equipment you are using.
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Old 13-04-2015, 03:12 PM
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Hi Simon.

Astrophotography is not easy, and that's the best part of it!

As for your graph, it seems to me that your mount is managing to correct traction for periods of time and then occasionally you get large drifting.

If I was to guess, I would say that there might be some play in your gear; maybe the focuser is not rigid, or tube rings, or maybe you have large backlash? Also, if any of the cords catches up on something it may also stuff up guiding.

Patience and perseverance will be your best allies in solving this issue
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Old 14-04-2015, 11:41 AM
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whzzz28 (Nathan)
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Originally Posted by Slawomir View Post
Hi Simon.

Astrophotography is not easy, and that's the best part of it!

As for your graph, it seems to me that your mount is managing to correct traction for periods of time and then occasionally you get large drifting.

If I was to guess, I would say that there might be some play in your gear; maybe the focuser is not rigid, or tube rings, or maybe you have large backlash? Also, if any of the cords catches up on something it may also stuff up guiding.

Patience and perseverance will be your best allies in solving this issue
All of the above and, make sure your clutches are tight (but not over tight).
However if you are seeing it once every 3-4min, then that sounds about right for a full gear rotation. Take a look at the gears to make sure they mesh properly, set the scope up inside and let it run in tracking mode and watch to see if there is any slippage.
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Old 15-04-2015, 11:01 PM
kens (Ken)
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Looks possibly like loss of the guide star to me. But not really enough info to tell whats going on. Why not post the PHD log file?
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  #11  
Old 22-04-2015, 08:27 AM
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speach (Simon)
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And it is!!!! Last night said to my self 'lets get this bloody thing working". Found out that it was the polar alignment that was the problem, got that fixed and bingo. The longest I've tracked for, up to now, is 20 mins, but I think it will go a lot longer than that. At 20 mins the stars are completely round.

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Old 22-04-2015, 08:52 AM
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rustigsmed (Russell)
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Originally Posted by speach View Post
And it is!!!! Last night said to my self 'lets get this bloody thing working". Found out that it was the polar alignment that was the problem, got that fixed and bingo. The longest I've tracked for, up to now, is 20 mins, but I think it will go a lot longer than that. At 20 mins the stars are completely round.

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