PHD Drift Polar Alignment.

[IvanT]

Well, the astro gods smiled on me last night. It stayed clear long enough for me to have a real good session learning PHD drift alignment. I think I've got it nailed but was surprised at how much (what I assume is PE) exists in my system.

Am I correct, is this PE in both RA & DEC?

[RobH]

You don't get PE in DEC, as it's not driving all the time, unlike the RA drive.

Re. Cone error, as mentioned earlier in the thread.

This only affects goto pointing accuracy, and has no effect at all on drift alignment.

As long as whatever scope you are using is pointing to a star in the right part of the sky for whichever axis you are aligning, it doesn't matter a jot whether the scope is aligned to the mount's axes.

I've been drift aligning using PHD for several years now....dead easy

Rob

[RogerTheDodger]

Ivan, what guide cam/setup are you using?

[IvanT]

Ivan, what guide cam/setup are you using?

I'm using the the SWE straight through finder supplied with the scope (9x50?) with a QHY5. Using EQMOD pulse guide settings.

[RogerTheDodger]

Thanks, I'm playing with modding a finderscope to guide with a webcam, I was amazed at the view you have in PHD - that QHY5 makes a big difference

[RobH]

Another tip with drift alignment in general....use the longest focal length scope you can, or if you only have short FL scopes, bung a barlow lens in.

This will show any misalignment very quickly, and if you can align accuratelly using a long FL, when using anything shorter guiding will be dead easy.

I finished my rig off the other night using my edge 11 at F10, so 2800mmFL.

Cheers

Rob

[IvanT]

Thanks, I'm playing with modding a finderscope to guide with a webcam, I was amazed at the view you have in PHD - that QHY5 makes a big difference

No problem Roger, I've found the whole thing a bit of a mine field but think it's down to me trying to run before I've learned to walk. With so few nights under clear sky it's difficult not to try and cram too much in.

Good luck with the finder scope mod. As you say, the QHY5 is pretty good.

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[IvanT]

Another tip with drift alignment in general....use the longest focal length scope you can, or if you only have short FL scopes, bung a barlow lens in.

This will show any misalignment very quickly, and if you can align accuratelly using a long FL, when using anything shorter guiding will be dead easy.

I finished my rig off the other night using my edge 11 at F10, so 2800mmFL.

Cheers

Rob

Thanks for the info Rob, but short of plugging the QHY5 into the 200P and drift aligning at prime focus, the finder guider is the only option I have for now. Do you think PHD drift aligning with a barlowed QHY5 at prime focus would be worth trying?

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[RobH]

Thanks for the info Rob, but short of plugging the QHY5 into the 200P and drift aligning at prime focus, the finder guider is the only option I have for now. Do you think PHD drift aligning with a barlowed QHY5 at prime focus would be worth trying?

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Anything you can do to get the focal length up is good.

Obviously, if you have a permanent setup, then drift aligning with your longest FL scope is well worth it.

Even without a permanant setup however, putting the QHY into the 200P and drift aligning, then taking it out, putting it into the finder guider and doing a PHD calibration run will only take 4 or 5 minutes longer at the most than drift aligning using the finder, but what you will gain, which may actually save time, is being able to see any drift much more quickly, and once you get used to it, you'll become pretty quick at alignment.

Rob.

[IvanT]

Cheers, my mount is on a concrete pier so I'll give the QHY5 at PF a try tonight, looking like it's gonna be another clear one.

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[bamus]

Gents,

Have any of you example screen shoot showing dx/dy graph before and after mount corrections? Reason I am asking is fact that when I was doing polar alignment using this method, blue graph - dx was responding to mount corrections, not red one as explained in the method. I am not sure if I have done something wrong or colours in Dx/Dy graph does not correspond to colours in RA/DEC graph?

[Ant]

I'm pretty certain that you have DEC guiding turned off.

Change the option to AUTO - I've circled the setting in your screen shot.

I'm going from memory - but I'm 99% certain that this will be your problem.

Cheers

Ant

[bamus]

Thanks Ant

This screen shot was done during polar align procedure, therefore guide in DEC had to be switched off. Important question is: in dx/dy graph, does dx represent N/S (dec) movement or E/W (RA) . If it is N/S, then correction must be made to this procedure as everyone seems to think that you have to look on Dy graph, not Dx

[themos]

If you click on the dx/dy button, doesn't it switch the graph to RA/DEC (which is what you want)?

[bamus]

themos

have a look on PHD polar Alignment description at the begining of this thread. DX/Dy movement has to be observed, not RA/DEC

[themos]

Drift alignment is always done by monitoring the Declination drift, whether you are pointing East/West or South.

[bamus]

Drift alignment is always done by monitoring the Declination drift, whether you are pointing East/West or South.

I am well aware of this I think you do not fully understand my question regardnig dx/dy graph. Have you done polar aligmnent using this PHD?

[themos]

Important question is: in dx/dy graph, does dx represent N/S (dec) movement or E/W (RA) .

dx/dy represents a mix of those two as the camera has not been aligned to the RA/DEC directions.

[themos]

have a look on PHD polar Alignment description at the begining of this thread. DX/Dy movement has to be observed, not RA/DEC

You are right, that's wrong.

[bamus]

ok, understand now (I hope) . in my case my camera must have been aligned 90 deg to RA/DEC direction. So to get this method right and be able to observe mouvment in Dy axis then camera has to be rotated in such a way that RA movement is in left right direction and DEC in up down direction. is it correct?

[themos]

No, the camera does not have to be rotated. Just let PHD calibrate itself first as if you were going to guide. And then make sure you are monitoring a RA/DEC graph (looking at the DEC drift) instead of dx/dy.

[bamus]

so then I have to keep guide in DEC on and disable guideing output. right? If I will switch guide in DEC, declination graph will be not shown.

[RobH]

Align your camera so the up and down on the screen is DEC, and Left/Right is RA (it's not essential to do this, but it makes it easier to read....also, you don't have to be exact)

Run PHD and let it calibrate (have guiding enbabled both for RA and DEC at this stage.

Then switch your DEC guiding off (you disable guide commands if you want, but will then see periodic error in the RA axis).

Lock onto the star you are going to use to align.

Tell it to guide.

You will see the star drift in one or the other direction in DEC (give it a few minutes).

Adjust your mount .

Simples

Cheers

Rob

[themos]

You want to let the star wander off in the DEC direction so the drift builds up and up. That's why you always turn off DEC guiding.

[chandrainsky]

Wanted to check if anyone in the forum has tried out drift polar alignment with the following combination: PHD softare + NexGuide (or SynGuide which is the same as NexGuide). I tried it out today and this is what happened:

I had connected the computer to NexGuide through the PC port on NexGuide. Since I dont have a RJ11 port to connect to the PC port, I used a RJ11 to USB converter. When I start PHD software, none of the camera options shows anything. Then I installed ASCOM and tried out. There was some response with the ASCOM camera option now but all I saw was noise (anyone remembers the noise that used to appear once upon a time on TV screens when there was no signal?). For the first few seconds I see "capturing" and then "star lost". There was no star on the screen to be lost in the first place!

Of course, certainly there is a star in field since I could see it on the NexGuide display - the star was almost centered on the NexGuide screen - but no star image appears on the PHD window. Tried various exposure times and different stars (from Sirius to a 4th mag star) but the result is the same.

Am I missing something? Or this combination does not work at all?