Polar alignment issue: Page 5

Polar alignment issue

curtismacc

P. Bombas Wouldn't it be possible for ZWO to include an option where the user manually performs an alignment to Polaris, after which the Seestar can calculate the deviations based on three other stars in different locations, without taking the level and compass sensors into account? In this way you avoid interference from external factors (materials) or am I seeing this wrong?"

All PA routines need a feedback system for the user to know what and how much to adjust the mounts mechanical alignment in Alt and Az. The Seestar uses the compass and accelerometer to provide that feedback. In the case of Non SMART telescopes, i.e. a standard telescope, the feedback comes in the form of viewing the star selected for PA through an EP or on a screen feed from a camera. The user then centers the star by adjusting the Alt and Az controls to achieve PA. ZWO could used the traditional method by showing us a PA star on the phone or tablet with a cross-hair for adjustment, but decided their way is easier for most users. It is very simple but, as we all have experienced, if there is anything out of calibration with one or the other sensor we get non-sense feedback.

Lilo

P. Bombas
Yes, use SkyAtlas to GoTo to the object, any.

braunschweiger

Lilo

I think you're completely misunderstanding something in this picture.

Let me try to explain how I do it in my own words (and it works very well).

EQ mode --> you set your latitude to 51°. A green checkmark appears.
Get Polar Align
Now you only need to look at the top two values! Not the
51° (or the deviation!!)

You just need to bring the top two values to zero (or
almost zero).

When the green checkmark appears, you're done.

Under no circumstances should you try to set the 51° again.

This is how it works for me, and it makes perfect sense, since the initial 51° setting is based solely on latitude.

In Get Polar Align mode, a more precise alignment is performed using three different stars.

Therefore, in this mode, the degree value of 51° (in your case) should be ignored, and only the two upper values should be considered and ideally set to zero.

Regards, Michael

Grahame

I’ve also been suffering with this sensor drift issue. Like the OP I’ve been seeing over 1deg/hour drift, even when powered off. I had been setting the Seestar up while there was enough daylight to make it easy, then just power up to polar align when ready to start imaging. I also found that a single iteration of PA was not accurate, except by luck, so I exited the EQ Mode page to redo a full 3 point alignment. I simply can’t do that now.

The Space Koala (Luca) has an excellent Utube video about why a single PA is, potentially, not accurate enough.

My suggestion would be to update the elevation figure on the Eq page with the calculated value, not the sensor value. Then either add an extra button or change the Refresh Deviation button to do a full 3 point scan again without having to quit the EQ screen .

Or use NINA.

3AC9bx99

Grahame Nina is the way to go. You get live feedback as you make your adjustments by plate solving not relying on the Seestar's internal compass or accelerometer. I can get below 0.1 degrees alignment. With the Seestar the deviation values bounce around so you never know if you are at 0 or not. Early indications are the subs keep rate at 20s and 30s improves as well. Am looking at this over the next few clear nights. Previously only achieving around 50% keep rate at 20s so hoping to significantly improve on that.

Grahame

3AC9bx99 yes indeed. Everything I’ve seen or read points to using Nina. Sadly however it’s Windows only, afaik, and I don’t have a usable MS device. My old laptop wrecked its 3rd battery after just a few years so I went to a MAC mini.
Being a poor old pensioner I’m reluctant to throw any more money at it.
Assuming a proper fix for the current issue is some way off, I’m hoping for at least a decent workaround can be figured out.

3AC9bx99

Grahame ZWO need to significantly improve the tracking capability of the Seestar in EQ mode. They should look at what Dwarf Lab are doing with the new Dwarf mini, that mini smart scope appears to work well in EQ mode at 120s exposure times.

curtismacc

Yes, NINA provides resolution down to less than 1 arc minute for PA while the Seestar only provides resolution down to 0.1deg which is 6 arc minutes. You could argue that really is 0.05 deg or 3 arc minutes, but it is still not as good as NINA's 3 Pt PA routine. Also, and in my opinion, more importantly, NINA does not use the internal sensors (compass, accelerometer) for the continuous feedback loop. It continues to take images and plate solves at the 3rd and final position after the initial 3 PT solution. So you get a continuous update via a plate solution. Seestar's internal sensors muddy everything as they kick in immediately after the initial 3 PT PA plate solution. So you can end up chasing your tail. I have already suggested to ZWO that they just continue to plate solve at the 3rd position and use that for feedback and silence the internal sensors. Then, one would only need to go back out of the routine and re-do the 3 PT PA if it is taking too long and the earth's motion starts to throw things off since one is not yet finished with the PA.

3AC9bx99

curtismacc I have been experimenting with NINA and I can get down to less than 1 arc minute for PA as explained. However this has not always improved my subs frame keep rate. On a trial run when I image objects towards the South my frame keep rate significantly drops off at longer exposures times of 20 and 30S. 60s is a waste of time. I have to use 10s for a good keep rate. However when I slew the Seestar to image to the North in the direction of the Pole star, my keep rate significantly improves with longer exposure times, I even had success at 60s. I believe this observation has been made before on this forum. So for my Seestar that is how I need to operate for good keep rates 10s for the South and I may go to longer exposure times for the North. Keep rates does seem to vary between users, whether this is related to a good or bad batch of Seestars is debatable or if there are other variables at play. But for the moment 10s for the South is best for me.

curtismacc

3AC9bx99 What you are seeing is the effect of drift due to the fact that the Seestar is not perfectly polar aligned. I am not saying that you did not do a good job of polar aligning your Seestar. Drift is a fact of life even in the most expensive mounts. I see drift with my $9K Software Bisque MX mount even after I use T-Point to do over 100 point polar alignment. We don't get field rotation since we are polar aligned, but we still get drift. Less the more accurate the PA and the better (in general the more expensive) the mount. The fact that you see more dropped frames when you point toward the celestial equator and less when you point north is due to the fact that the "apparent" motion of the object is greater looking near the celestial equator and less when looking near the celestial pole. Think of a time lapse image of star trails taken with a stationary camera. The stars' arcs are longer closer to the celestial equator than they are are the celestial pole.

3AC9bx99

I don't know what more I can do if you say I'm not perfectly polar aligned despite getting down to 1 arc minute or less. Even the new DwarfLab Mini from the videos I've seen, at £360 can seem to image quite happily at 120s exposures with minimal polar alignment effort. I do think ZWO can improve on the alignment process. I will repeat the NINA process and see how I get on.

curtismacc

3AC9bx99 No telescope is ever perfectly polar aligned. Assuming that you are as aligned as one can get with the Seestar, then the problem is in the Seestar's mechanics. This is a $550 all-in-one telescope so the mechanics will never be as good as a mount costing as much as or more than the Seestar itself. Also, it is clear that there is a significant variation in the manufacturing tolerances on the Seestar's mechanics as some folks report few dropped frames and others many dropped frames.

Bottom line, adjust the PA as best you can with the effort you are willing to put in and then live with the result.

As far as the Dwarf Mini, I have also seen folks report as you say. I have one coming so I will be able to test it myself. Keep in mind that the wider field of view vs the S50 helps to minimize the apparent motion as well, but maybe the mechanics in the Mini are better. We don't know at this point, but time will tell.

3AC9bx99

curtismacc Totally agree. It will be interesting to see your take on the Dwarf Mini.

« Previous Page