Phd2 doesn't agree with polemaster

[Hitesh]

Im completely rubbish at polar alignment so I got myself a polemaster to aid and speed up the process. I know the manual is pants but I have seen loads of videos on the tube, and I have been able to follow what's going on, and managed to align the scope. When I tried to verify the alignment with Phd2, a huge alignment error is shown (-104). I've also found other problems like non orthogonal axes when calibrating PhD. Has anyone any ideas on solving these issues? God I wish this hobby was less frustrating

[Thalestris24]

Hi

Can you post a screen dump of your phd2 drift alignment? It's hard to see how you could have an error of 104 mins!! Make sure you're trying to align in the right direction - it asks for azimuth first (south) then altitude (east or west). Don't rely on the guide assistant PA numbers - they seem to be instantaneous values so you have to be wary especially if seeing isn't so good.

Louise

[kens]

Or better still, post the PHD2 guide log from the session in question. It is usually located in your documents folder in subfolder PHD2. If you don't have a clean calibration then PHD2 doesn't work as it should

[Hitesh]

Ok guys heres the phd log from last night i hope it means more to you than it does to me

PHD2_GuideLog_2016-05-07_231534.txt

[kens]

You've got a bunch of problems there. First up your calibration in PHD2 is off with the two axes nowhere near orthogonal. In this log you used the calibration that was done in an earlier session (at 10:34 PM). Post that log file as well so we can see what happened during the calibration sequence. Without a good calibration PHD2 cannot work out your polar alignment

Another thing I see is that you have a very high signal to noise ratio so I strongly suspect that your guide star is saturated. Next time switch on the star profile display: Menu View > Display Star Profile. Check that the star profile has a pointy top and not a flat top.

 

[Hitesh]

Thanks for that, I will definitely look into that, and I will try and post up the earlier calibration. How do I sort out the orthogonal axes issue? 

[Hitesh]

What sort of signal to noise ratio should I aim for?

[Davey-T]

8 minutes ago, Hitesh said:

Thanks for that, I will definitely look into that, and I will try and post up the earlier calibration. How do I sort out the orthogonal axes issue? 

Check your balance, my mount gives orthogonal warnings in PHD if the balance is off.

Dave

[Hitesh]

here are the other logs from the night. My balance is off, i think i need a longer dovetail and offset the scope to bring it into balance but that makes me think is there enough clearance for the focuser if i push the scope forwards towards the objective lens to bring scope into balance.

PHD2_GuideLog_2016-05-07_220034.txt

PHD2_GuideLog_2016-05-07_222222.txt

[kens]

That's a pretty bad calibration.

You need to adjust the calibration step size. Go t o the guiding tab on the brain and click Calculate. Then enter the appropriate values.

If you are using ST4 guiding then make sure you enter the declination where you are doing the calibration.

Also make sure the guide rate is the same as you have in your hand controller or EQMOD. And ideally at 0.5 or 1.0x sidereal. It looks like you are guiding at 0.3.

Why did you do the calibration with ST4 guiding then switch to EQMOD pulse guiding? If you are happy with EQMOD then I'd suggest calibrating with that setup also.

You should calibrate either close to where you are imaging or, if you plan to reuse the calibration, close to dec 0. From the data in your calibration either you were calibrating with a different guide rate on RA from Dec or you were calibrating at around Dec 75 degrees

Make sure you have a good calibration before doing anything else with PHD2. Otherwise it simply wont work.

 

[Hitesh]

Thanks for that, I think I will stick with EQMOD, one less cable hanging around that way. So do the RA and DEC guide rates have to be the same? 

[Davey-T]

2 minutes ago, Hitesh said:

Thanks for that, I think I will stick with EQMOD, one less cable hanging around that way. So do the RA and DEC guide rates have to be the same? 

You need the RA guide rate set to keep up with sidearal rotation, in a perfect world dec wouldn't need to guide .

Dave

[kens]

Don't mix up guiding with tracking. The guide rate for RA should be 1 or less so that eastwards corrections work by turning off the tracking temporarily. Guide rates more than 1 cause eastward corrections to reverse the motor direction which leads to backlash.

The guide rates for RA and Dec do not need to be the same but there's also no reason for them to be different. So you may as well keep things simple.

[Davey-T]

Thought I read somewhere that PHD doesn't reverse the RA motor just stops until it catches up, can't believe everything you read though, unless it's in the Daily Mail 

Dave

[kens]

Its not controlled by PHD. Its the motor controller that determines it. All PHD does is to tell the motor controller to guide East for xxx milliseconds based on the guiding rate and the amount of correction needed. If the guiding rate is less than 1x sidereal the motor controller should just stop for the appropriate time. e.g. If it is 0.5x sidereal it will stop the motor for xxx/2 milliseconds or alternatively it could send out only half the tracking pulses for xxx milliseconds

[Hitesh]

Finally a clear night to test everything again. I've managed to put the scope on a longer dovetail ( thanks for that FLO great service as usual) and shifted the tube up towards the objective lens, this has massively improved my scopes balance and PhD now sees the axes as othogonal with a smallish error, this is can live with for now ( thanks Davey-T for the suggestion) . And having calibrated properly today I even got a very low error on my polar alignment so looks like my original problems are felt with. Now to learn how to guide properly!!!! ??? God I love this hobby when things work