PHD Drift Alignment problems

[SimmoW]

Gawd, last night was hell. I spent over 4 (!!) Hours chasing the PhD drift alignment trend line.

I learned one good thing, to make sure each exposure was at least 2 secs to avoid the tortuous 'chase the seeing' scenario (it finally dawned on me after a brief 2 hrs..)

But even after seeing a settled trendline, I started guiding and the guider was struggling to keep up, jolting all over the graph.

I tried a different, heavier balance weight, only barely differeny, could that be it? Even after doing a synscan polar alignment, the graph was off the scale and very , very hard to level out. One small adjustment would cause the graph to go opposite direction, almost vertical!

And I was Going so well before! Last week I found the alignment process much easier. Could it be the new version of PhD?
Simon

[codemonkey]

I feel your pain mate. I've been struggling with PHD for a little while now with no success.

One thing to note when doing drift alignment is that tiny adjustments can go a long way.

Hopefully it's ok to link to other forums here, but have a read of this thread for some suggestions on drift aligning, it helped me out a lot: http://www.cloudynights.com/topic/472874-drift-alignment-with-phd2-the-bookmark-technique/#entry6172443

Drift aligning isn't the problem for me it's actual guiding. No matter what I do I can't get that to work well. I've finally got DEC guiding working well enough by making the scope even more east heavy, changing the minimum move to 0.6px and the guide length to 250ms. My RA is off the dial though, completely random it seems.

Last night I ended up giving up because my ram was getting far too interested in me and my equipment (even rearing at my mount and trying to eat the cables) but before that I had the... I think it's the "RMS error" or something, was reading 0.4 on DEC but 2.5 on RA... worst I've seen on RA yet. Driving me nuts because I have lots of new toys but this is preventing me from actually doing anything with them :(

[lazjen]

I can't see any posts on the forums (Google Groups) suggesting any issue with 2.3.1 (which reminds me I must update).

Do you use astrotortilla at all? It's got a PA routine I find much easier to use without the need for tedious drift alignment.

[codemonkey]

One thing I noticed last night as I was packing up was that I was doing 3s exposure with the guide cam and the star had a SNR of 3.8 ... after googling around people are getting SNR of 20+ and seem to have problems with less, so that might have been a particularly bad star for me to be trying on, thus causing some of my issues, so it's something for you to consider also. I haven't seen over 7 though, and 20+ sounds crazy good.

[lazjen]

Lee, I often guide on stars around the SNR of 3+. Anything less than that generally doesn't work for me.

[SimmoW]

Thanks Lee , that's a useful link, bookmarking will certainly help! Damn it's frustrating, esp when it was so good the last few times. Another issue for me was my altitude adjustment was a whole degree off because I'd used the mount in the country. But I'd already adjusted it back using Synscan. But after that the results were still pretty poor. Is Synscan that bad? Should I be using an external controller?

Thanks everyone

[Andy01]

Simmo,

Here's my PA routine with PHD 1. This works well for me.

Drift Alignment (with thanks to Chad Gray)
I point the mount south as best I can, using a compass (not the iphone) or solar noon method and allow for the mag deviation for your location. (11* 36'44" east for Melb).

Level it using my own spirit level. I use an inclinometer (bunnings $35) to set the alt scale to my present location co-ords (37.5 in Melb).

I do a quick & dirty one star alignment to get everything running, then point the scope just north of the zenith and find a brightish but not saturated star. Calibrate PHD on the star then stop tracking. Turn on the graph and change to DY/DX display. Click the brain and turn off DEC guiding. Start guiding on the star.

If the DY line drifts up or down then adjust your physical azimuth knobs on the mount until the graph stops drifting up or down. If the red line drops or climbs vertically then your initial placement of the mount is way off relative to true south. I have been known to pick up the whole damn thing and turn it out of frustration at this point! Not recommended however! Better off getting the mount pointing accutately true south first :)

Once the red line is as flat as possible, Move the 'scope and find a star as low as you can on the east or west horizon. Click the brain and force calibration. Turn back on DEC guiding. Calibrate on your star. Stop guiding. Click the brain and turn off dec guiding. Start guiding on the star. If the DY line drifts up or down adjust your physical elevation knobs on the mount. (Assuming you have preset this accurately, any corrections will be minimal.)

Now your mount is polar aligned. Now run your mounts alignment procedures on your alignment stars so you can find things in the sky.

This method gives immediate feedback and no waiting. The original idea/instructions on this web site:

http://njstargazer.org/PolarAlignment.asp

I havn't adjusted to phd2 yet, I found it fiddly but that tutorial link posted above may help!

Cheers
Andy

[Andy01]

Ps: make sure your 'scope is perfectly balanced first, in both ra & dec, or you'll encounter major problems with backlash! Not doing this cost me half a nights frustration last year!

[SimmoW]

Thanks Andy, glad to know I'm not the only one who wants to physically move the mount in frustration! I'll give it another go tonight, though I doubt I'll do any imaging, just jump with glee if I can repeat the guiding results of last week.

After Paul's presentation at ASV, I thought I was pretty careful with my south alignment. I finished off fairly aligned last night (after 4 hrs!), have left the mount up in our glorious weather, so I should be off to a good start tonight. Famous last words...

Hey, can you post/send me a pic of your inclinometer. I have no idea what I'm looking for in Bunningsland

Ta

[codemonkey]

Ah, thanks Chris. Well, there goes that idea. I'm hoping my issues are related to cable drag which should be fairly simple to fix, if not that then I have no idea.

[SimmoW]

Bugger, another 90 mins of frustration. How come I found it so easy before? Now I do a pretty good Synscan alignment, but straight away the PhD drift alignment graph goes off the chart.

It took ages to level out the first Dec line. But then the altitude line got much worse. So I corrected that, then the RA went right off again! I get so confused after all this chasing, the mount head ends up being nowhere near aligned.

At the end I just could not fix the alignment, even just a tiny adjustment threw off the graph.

I might try to reinstall v2.3.0, I wonder if 2.3.1 is buggy?

I checked my balance, it's no different to before. Pretty good for the design of my stumpy scope.

Are there any other good alignment packages other than PhD? I tried v1 but couldn't get it to calibrate, let alone guide.

[SimmoW]

And I'm wondering, why should the altitude knobs constantly need adjustment? I'd think that once it's aligned, it should stay pretty fixed.

[Amaranthus]

Altitude shouldn't need re-adjustment, provided you've not changed latitude. Do it (alt) well, once, and then just refine azimuth for each new session.

[codemonkey]

I'm not sure about Simmo but I've got my scope on an EQ6 with a tripod on soil. Alt is definitely different day to day, usually a couple of arcminutes. I'm not sure how close you need to be with guiding so maybe I could get a couple of sessions out of it but that'd probably be about it.

[Andy01]

When playing with phd 2 last time, I noticed the scale is much more unforgiving than phd1. Try phd1 again using my aforementioned method for an experiment and see how you go, once you nail it you'll never look back! That said, I'll try phd2 again and see if I can nail it there eventually.

[SimmoW]

Yep, I'm going to try the earlier version of PHD2 as I found it much more forgiving, then maybe 1, and if desperate, will try metaguide.

I know my guidecam, an ASI120mm, has idiosyncrasies with some guiding programs, so maybe the latest beta is nerfed. Better be, as if it's not the guiding software, something has happened to my (pretty new) mount. Which is hard to explain as I cradle it like a newborn when carrying it.

Will keep you all informed!

[Amaranthus]

PHD2 and Metaguide both work brilliantly with my ASI120MM - but run it via pulse guiding and forget about ST-4.

[SimmoW]

Hmm, good idea. Now, what do I need to do pulse guiding? What type of cable do I need, from Pc to the mount? I know nothing about such things!

[Amaranthus]

No new cable, it is all done via the serial-to-USB connection.

[SimmoW]

Barry, I'm not sure what you mean, I don't have an existing USB to (is it?) RS232 serial cable, as I'm just using my synscan controller direct to the mount.

So if I google a decent length USB to serial cable (9 pin?) that'll be the one?

Thanks

Simon

[Amaranthus]

Simon, how are you connecting the computer to the mount? Whatever cable you are using for this (not counting the ST-4 cable) is what is used for pulse guiding. I think from what you say you are doing it in PC-DIRECT mode on Synscan, which is fine for using pulse guiding. Basically, just ditch the extra ST-4 cable, and turn on ASCOM pulse guiding. This has another advantage - if using EQMOD, you can also use VS-PEC with no clash with AG.

[SimmoW]

Barry, I connect the laptop to the camera via a usb cable, not sure what to call the other end. Then another cable goes from ASI camera to ST4 on the mount.

[Amaranthus]

Ok, then you need a serial to USB adaptor, or better still, an EQDIRECT cable, if you want to pulse guide.

[SimmoW]

Thanks Barry, I'll remember that.

Seems that it might indeed be a PHD2.3.1 issue, the below thread is similar to my issue. I'll go bak to 2.3.0 asap since that was working so well before.

http://zwoug.org/viewtopic.php?t=1729&p=3059