Seestar S50 drifting: Page 3

Seestar S50 drifting

bakosmi

A very small window opened few days ago, so i did another trial.

My Polar alignment:

Nonrejected pictures - 30s exposures blink

horsehead.mp4

6MB

9:31PM - 11PM - so hour and a half and clouds came but alnitak was still visible so i kept it running.

I would assume backlash would settle, but seems like it did not and i had dithering on.
I will also try to turn off the dithering next time as the way it "wanders" maybe not another dithering is needed ? :-)
I know from my past short time with iExos-100 and 400m lens, that tracking is affected by the target declination, but i wasn't expecting so much issue with the Seestar S50.

I had no chance to try it without 3.0.0+ updates as I have unknowingly updated it right after unpacking. :-(

bakosmi

is my polar align on the picture actually so bad it could prevent 20s exposures ?

Daemon42

curtismacc Yes that is possible, and have indeed see more crosstalk between axes during PA calibration if it's not levelled. But after a couple cycles through PA calibration to the point I'm < .3 degrees on both axes, it shouldn't matter any more, but still seems to. I do notice one other odd glitch while doing PA.. If I find I have move a lot.. say 3-4 degrees on AZ as I am turning the screw on the EQ mount and getting close, ala.. 3.. 2.. 1.. .6.. .3 <it sticks right here> I'll keep turning the screw and it just stops showing any change to the value, for about 3-4 seconds, and then it either claims I'm at/close to zero (when I know I've turned the screw more than that) or it shows overshoot. My subjective impression is that there's a glitch here, where as it turns the display of the numbers from red to green.. it stops actually registering changes for a couple seconds, and actually messes up the PA. I find that if I stop turning the screw right at that moment the color changes, wait those seconds, then I can fine tune it more accurately.
It seems to be more of a problem when I'm coming in from a larger initial deviation (maybe because I'm turning the screw faster), so the other thing I do is just always put my tripod in the same place, and try to visually align the scope with a particular target (center of a tree about 50ft away) so I'm usually starting no more than 1-2 degrees off angle.

bakosmi

Daemon42 i have the same issue - it freezes when i finally should be close. i have to re-check the error via button or restart whole pa or do a big change in any axis.

Daemon42

jgood This is the rail.. https://www.amazon.com/dp/B0CBV87NM9?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1

And this is the spacer https://www.amazon.com/Manfrotto-120-Spacer-Tripod-Columns/dp/B001FCN1TE/ref=sr_1_10?crid=10TIPI1XJ7QMU&dib
Yes it's about 2" in diameter, so supports the scope optimally.

And FWIW, this is the EQ mount. https://www.amazon.com/dp/B0CLVM66M2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2
But it's not available any more.
Something like this should work
https://www.amazon.com/NEEWER-Panoramic-Millimeter-Adjustment-Aluminum/dp/B0FB3G7PKF

Daemon42

xalex I'm a bit skeptical of the idea of it having a "baseline speed" that only works in one part of the sky. There's nothing that complicated about the math. It knows exactly how fast it needs to drive to track no matter where it points in the sky. With 20s exposures I do not see anything to suggest that the tracking during initial captures is too slow or too fast, and I regularly shoot stuff both very high (closer to north pole) and out near the ecliptic. I'd be more suspicious of it just being lost in the gear lash after any larger movement but with a 30s exposure it should take up all the lash in one frame.

3AC9bx99

Reading around the subject of frame rejection rates, excessive dithering may play a part in this. With the Seestar app there is no way of adjusting dithering, it is fixed. I'm no expert in this but would reducing the dithering help with frame acceptance rates. In NINA software I know dithering can be controlled, do you get better frame retention when using NINA compared to using the Seestar app

curtismacc

3AC9bx99 Good question but I don't think there is any way to accurately compare the two. NINA does not reject frames, it captures everything. So, one would have to set up criteria in a post processing software like Siril or Pixinsight, etc. to reject frames. There is no way to know what the exact criteria the Seestar Stacking algorithm uses so also no way for a direct comparison.

What one could do is capture images with the Seestar App and with NINA using several different dithering settings and then use post processing software to determine the ellipticity , HFR, FWHM, etc and compare among the different dithering settings.

3AC9bx99

curtismacc I think I will continue to save all the frames in the Seestar app on a low declination object and stack with one of the scripts in Siril and compare the frame retention rate with the Seestar stacked image. May show nothing but worth a shot. With your M81 image with a frame rejection rate of 0-2.4% and with M42 at 47.5-51% rejection I take it you were using NINA. If so do you know what dithering setting you used.

curtismacc

3AC9bx99 I was using the Seestar App. As I said NINA does not reject frames. The rejection rate you will get in Siril certainly will depend on the criteria it uses. It could well be that the Seestar App rejects more frames than necessary.

For the record, plotted the frame rejection rate versus cosine of the declination of the targets for targets from -2deg to 69deg (M81). The data fits a straight line with an R-squared of 0.8 which is extremely good considering all the other things that can cause frames to be rejected. I will publish this along with other data on frame rejection rates after I finish summarizing my results and post them on my YouTube channel.

Best Regards,
Curtis

3AC9bx99

curtismacc I'll subscribe to your channel to make sure I catch it.

Nasa-HSIA

curtismacc May I ask what the latitude of your location is? What is the rejection rate performance at Dec. smaller than -2 deg?

3AC9bx99

So if NINA does not reject frames how do you get a final image out of it. Does NINA stack frames, use a plug-in, do you need to transfer saved fits file to an external program like Siril for stacking? I sometimes use NINA just for the polar alignment step as it is more accurate.

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