“Star trails detected, cannot stack, image discarded” after last firmware update

Winchester

Hello, last night I updated the Seestar app to the latest version and downloaded the firmware in my S50. After days of bad weather, I was finally able to try the equatorial mode by mounting the TH10 head on my S50. Just below I mounted the leveling base for an optimal bubble setting (although someone, told me not important in eq mode). Subsequently performed eq mode calibration following the advice for a perfect polar alignment. Set the click to 20s and a plane (in order to perform multiple sessions) in mosaic mode to capture the "Horse's Head" nebula and the "Flame" nebula. As soon as I start the plan, everything goes as planned, but I start receiving video messages, “star trails detected, cannot stack, image discarded“. Moral of the story, in 2 hours of shooting, only 20 minutes acquired. I don't understand, I bought the equatorial head just to be able to increase the exposure times and zero the discarded shots. The sky was perfect, there was only the moon near Orion to bother, but I don't think this is the problem of "creeping". In the calibrations I was very patient and precise. I read on Google that someone is experiencing problems with stars crawling with relative shots discarded after the last firmware update. Could someone give me some indications? Thank you.

3AC9bx99

You are likely to be experiencing severe star trailing due to the declination you are viewing at, where objects with low declination angles such as the Horsehard Nebula at Dec -2 degrees will experience a lot of star trailing. Apparently some Seestars are better at tracking low Dec objects than others but yours just like mine seem to struggle when you use long exposure times of 20s or more. I have to use 10s max with low Declination objects in EQ mode otherwise I experience a lot of dropped frames. I can only start to use 20s or more at much higher declinations of 50 - 60 degrees. I know some users have found recalibrating the compass and level sensor after a firmware update has a beneficial affect, but this does not get round the phenomenon of declination drift.

Winchester

3AC9bx99 So you're telling me that I'll never be able to take 20-second shots on objects with a declination of less than 2º??? Is it possible that this problem will not be solved with an update from ZWO?

3AC9bx99

Winchester Unlikely, but see what ZWO come up with in future updates, but my Seestar has been like this since EQ mode became available. This assumes your polar alignment is spot on. If you are using the Mosaic mode you may be better with 10s subs regardless, as it takes a lot longer to complete a full frame with 20s and if you are at a low declination the frame loss will compound the final quality of the image. I would suggest experiment with 10s and see if your frame retention rate improves. Then see how it performs with different objects at various Decs and different exposure rates, you will then know how your Seestar behaves.

Winchester

3AC9bx99 Thank you for the answer. But is there a way to make this problem of declination known to ZWO? Also because it would be a shame for users who encounter this problem of declination not to be able to take advantage of greater exposures in eq mode on objects with low declination.

3AC9bx99

Winchester I'm sure ZWO are aware of declination drift. I will convey my experiences with the Seestar S50 regarding it through their on line support page. Feel free to do the same. Look out for an expected YouTube video on the subject by Curtis. Read the discussion under "Seestar V3.0.2 has been released" on this forum.

curtismacc

Winchester Declination drift is a long know phenomenon in astro-imaging in EQ mode. Simply put, when the Polar Alignment is not perfect (which it never is) objects will appear to drift in declination as the mount does its best to track at sidereal rate. In fact, declination drift has been used to achieve accurate polar alignments long before plate solving became available since the drift provides the information needed to adjust the Altitude and Azimuth of the mount to minimize the PA error.

I am not sure whether the differences in dropped frames from one person to another at different declinations is due more to their differences in PA accuracy or also in differences in their Seestar themselves. This would be a very hard thing to measure even if I had multiple Seestars, although I have thought about purchasing 2 more S50s to test. Fortunately none are available right now so that thought has passed.

Regards,
Curtis

55u56qWD

I have had similar problems on both S30 and S30Pro. I found that closing the arm and reopening it fixes EQ tracking. I can then do 20s or 30s exposures for hours with hardly a dropped frame.

3AC9bx99

55u56qWD That's a good result but at what declination are you imaging at? A lot of folks claim good frame keep rates but don't always say at which declination the object is at.

3AC9bx99

I've just had success with imaging M108 at Dec 55 degrees using 30s exposures but using the continuous imaging mode. I initially set 500 exposures, after deleting a few frames for satellite trails and clouds I got a 100% stack of 495 frames using the deep sky stacker function. In Live mode I would not expect to get that level of successful stacks. It may be the live stacking algorithm is different to the deep sky stacker function. I need to do more experiments at lower declination angles but an encouraging result.

curtismacc

3AC9bx99 Declination drift for objects at 55deg declination will be much less than objects close to the celestial equator. The true test is something close to 0deg dec. M42 is at -5deg and NGC2244 is at +5 deg. Good targets to try, but they are getting further from the meridian after dusk these days.

7RZPFJfJ

My S30 Pro has completely no tracking in EQ mode. The target will move out of frame in few min.. Both RA and DC gear have very large amount of play. Last try was an object declination of 26 degree and with alignment error of 0.1.

curtismacc

7RZPFJfJ Try M81 or M82 at 69deg declination. If you don't get in the 90% capture rate with either of these you either have really bad PA or something is else is very wrong with you setup or unit.

3AC9bx99

curtismacc That is my plan, these are good low declination objects to go for, though may be low in the sky to clear obstacles from my back yard. Will give them a go in both Live and Continuous capture.

Léon323

I have sometimes noticed that temperature can also have an effect on this problem (outdoor temperature e.g. +0 degrees). Before the moment of observation, I have balanced the camera tripod outside (I a, using separate video tripod). At the beginning of the observation, I bring the Seestar S50 from the inside out and do the polar alignment according to the instructions. Usually, after a few minutes or maybe 10 minutes, the device will start notifying you about the alignment for the first few pictures. I go to do the polar alignment again and after this the device no longer gives error messages.
That was interesting information about low inclination targets. I've noticed that the images are sometimes blurry or have streaks, for example, when I use 20-second exposures. Great tip, I'll try with 10-second exposures in the future.

3AC9bx99

Léon323 Good point about temperature. Generally if I can I place my Seestar outside about 1/2 -1 hour before starting imaging to allow the unit to equilibrate to the outside temperature. Helps with stable focusing.

francescoCh

Just adding my two cents here.
A few months ago I made a thread about the S30, EQ mode and mosaic. Even sent images to zwo.
My conclusion is that for whatever reason, mosaic and EQ mode do not mix at all as percentage of rejected images is at least 50% at 60secs exposure. The surprising thing was that decreasing exposure did not improve that figure, it even made it worse. As a reference normal EQ mode at 60sec has a 10% average rejection.

Given the lack of clear skies where I live, I decided to use manual mosaics instead (for instance the markarian chain) even though I'm not very good at it yet.

7RZPFJfJ

I am confused with one thing. The declination drift should be producing the star trail at north-south direction.
But the S30 Pro 's IMX585 is in portrait mode. The sample we have all show the star trail in east-west direction. Is this supposed to be the RA drift?

3AC9bx99

7RZPFJfJ I'm sure other can correct me on this but the visible drift rate is affected by the cosine of the declination. So at the Equator at Dec 0 degrees, Cos (0) = 1 so stars appear to move at their fastest rate. Near the Poles
Dec of 90 degrees, Cos (90) = 0 so stars appear to move very slowly, traversing a small circle. So at lower declinations as you approach the celestial equator, more precise tracking is required otherwise stars produce long faster moving trails which is what you are seeing in the images. To minimise star trailing at lower declinations a shorter exposure time is recommended, whilst at higher declinations the exposure time can be increased.

7RZPFJfJ

3AC9bx99

Thanks for the comment. Just for reference. That sub was taken for a object at DEC of 26 degree. I had another session for a object of DEC 48 degree. It is not much better.

The site is located at southern hemisphere. Assuming this should not make any difference apart of different RA/DEC for the given object

curtismacc

3AC9bx99 You are exactly correct in your description of the sensitivity of declination drift.

3AC9bx99

7RZPFJfJ RA/Dec are the same for everyone wherever you are on Earth. What changes is the Alt/Az for your particular location and time of day. The discussion under "Seestar V3.0.2 has been released" may be of interest to you.