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Could Star Trails Still Be An Issue In Seastar's EQ Mode?

ZWO Seestar S50 Star Tracker NGC6960 Supernova Remnant Deep Sky
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Szijártó Áron avatar
Szijártó Áron avatar
Hello and welcome, I'd like to ask whoever is using the Seastar in EQ mode, or uses the TH10 Tripod head, or any Equatorial equipment with the Seastar, or just has experience in this.
Last time I was capturing the Veil Nebula, and at 42 exposures, the seastar began to say that it detected star trails, which I don't know how. Cause The EQ mode could have solved all the issues that the Seastar is struggling with.
So I said Wait, what?
How could that happen?
I literally polar aligned it to follow the Earth's rotation, yet it can still detect star trails.
So I had to ask, is this still possible to happen even in EQ mode, or has it happened because I wasn't really properly setting the seastar to face north or something?
Although using the TH10 fluid tripod head was totally worth it cause it's smoother to set up than the Skywatcher wedge.
 So, can anyone confirm what is causing this or why this can still happen?
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Tony Gondola avatar
Tony Gondola avatar
How accurate is your PA? To get no trailing in a 10 sec. exposure it has to be pretty close.
Peter LeFebvre avatar
Peter LeFebvre avatar
Star trails can happen even if you are set up in EQ Mode properly due to multiple factors.
  • What is the exposure length you have set?
  • How many frames are getting dropped due to star trails detected?
  • Did you get to near zero for latitude and north orientation during EQ calibration?
  • Is the Seestar close to level?


Wind can cause star trails, Seestar is very light. Make sure your tripod is stable and weighted down if possible. Keep the tripod legs short as that minimizes flex and vibration. If the tripod is on grass or turf vs solid surface use spikes as otherwise it shifts over time causing star trails. Get as close to level as possible. Perform "Get Polar Align Deviation" every time you set up for an imaging session. Setup I use is below.

I do not get 100% retention of frames but get good yield with this setup even using 60s exposures. 10 and 20s exposures nearly 100%.


Seestar - Low Cost EQ Mode Setup
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Szijártó Áron avatar
Szijártó Áron avatar
Tony Gondola:
How accurate is your PA? To get no trailing in 10 seconds. Exposure, it has to be pretty close.

The current altitude from which I started is 47 degrees. And the alt AZ values were 0.9 and 0.3, the polar alignment values, and the altitude was 52 degrees where I finished the setup.
It was like it was close, but you can tell it wasn't perfect. I do wonder how you can achieve a perfect polar alignment.
Jeremie Chapin avatar
Jeremie Chapin avatar
As with Alt AZ, Eq mode will also get star trailing. Eq mode is just slightly better, but will have its trailing issues too. Just make sure to get the best polar alignment you can and that is all you can do. I have those issues too with 10s, 20s, 30s and 60s. If it happens a lot, would recommend calibration of the compass as it has helped me with constant star trail messages. 

Clear skies my friend!
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Oscar avatar
Oscar avatar
Szijártó Áron:
were 0.9 and 0.3


@Tony Gondola these PA numbers are in degrees btw
Craig Rairdin avatar
Craig Rairdin avatar
EQ mode helps eliminate star trails caused by field rotation. This makes longer exposures possible. My experience is that I get the same results at 20 seconds that I used to get at 10. Others have better results.

The ability of the Seestar to accurately track across the sky also affects star trails. You can't do anything about that.

Putting a wedge under the Seestar means it is no longer centered over its mounting point. This makes it less stable and more affected by wind, vibration from whatever you might have it sitting on (concrete is preferred) and motion caused in response to normal motion of the scope in operation. If you can offset the wedge to keep the center of gravity of the Seestar over the center of the tripod, that will help make it more stable. I like the balance arm and eq mountsfrom https://petersonengineering.com/seestar-stuff for addressing this issue.

As others have mentioned, securing your tripod helps. Shortening the legs doesn't. The legs should be fully extended to give you a larger base. The tripod should be level and PA should be as good as you can get it.
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Noah Tingey avatar
Noah Tingey avatar
Are you sure that it was field rotation? My understanding is that field rotation only occurs when you are guiding, as it's a function of guide star angle as per this. 

I suspect you are talking about declination drift.
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frankyastrobin avatar
frankyastrobin avatar
Hi, I use EQ mode. At beginning in EQ I often had lost frames and star trails. This happend, because my S50 was placed directly on the earth/gras in my garden. But this ground is too soft. When the S50 is rotating, then the torque-power from rotation can't be fixed by the mount. Now a heavy concrete-plate is place on the ground, and the S50 is place on the plate. This is stable, and the mount provides a stable basis for the S50.

And, I never use 60sec. 20 sec is my favourite. 60 sec frame produces to much brightness, some stars become over exposed. And, in 60sec mode too much time is lost if a frame is deleted. My experience is, the 20sec generates best ration of exposure time/lost time.

The polar alignment must be exact if 60 sec is used. At 20sec the alignment can more inaccurate.
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Szijártó Áron avatar
Szijártó Áron avatar
Noah Tingey:
Are you sure that it was field rotation? My understanding is that field rotation only occurs when you are guiding, as it's a function of guide star angle as per this. 

I suspect you are talking about declination drift.

Declination drift? Like you mean, I wasn't perfectly aligned it right, or it wasn't perfect?
Noah Tingey avatar
Noah Tingey avatar
Szijártó Áron:
Noah Tingey:
Are you sure that it was field rotation? My understanding is that field rotation only occurs when you are guiding, as it's a function of guide star angle as per this. 

I suspect you are talking about declination drift.

Declination drift? Like you mean, I wasn't perfectly aligned it right, or it wasn't perfect?

Declination drift is the drift that happens if you are not perfectly polar aligned and if you are not guiding. 

You mentioned that you got within 0.9 and 0.3 degrees of alignment. This is still pretty far off alignment, at least from my experience. With my 1.4"/px setup, I make to sure to get within 1 arcminute, for reference.
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Szijártó Áron avatar
Szijártó Áron avatar
Peter LeFebvre:
Star trails can happen even if you are set up in EQ Mode properly due to multiple factors.
  • What is the exposure length you have set?
  • How many frames are getting dropped due to star trails detected?
  • Did you get close to zero for latitude and north orientation during EQ calibration?
  • Is the Seestar close to level?


Wind can cause star trails, Seestar is very light. Make sure your tripod is stable and weighted down if possible. Keep the tripod legs short as that minimizes flex and vibration. If the tripod is on grass or turf vs solid surface use spikes as otherwise it shifts over time causing star trails. Get as close to level as possible. Perform "Get Polar Align Deviation" every time you set up for an imaging session. Setup I use is below.

I do not get 100% retention of frames but get good yield with this setup even using 60s exposures. 10 and 20s exposures nearly 100%.


Seestar - Low Cost EQ Mode Setup

As of right now, im going towards 30 seconds of exposure cause I want to bring everything the seastar can do, especially in EQ mode.
At 42 integration time, it only dropped 1 frame, although I can't tell exactly how much it dropped. I only noticed how long it takes till it proceeds to continue the work.
The alt AZ  values were 0.9 and 0.3. The azimuth value was closer to 1, but the altitude was way closer to being perfect. And speaking of leveling, I havent really checked if the tripod or in general the setup was leveled.
Szijártó Áron avatar
Szijártó Áron avatar
Noah Tingey:
Szijártó Áron:
Noah Tingey:
Are you sure that it was field rotation? My understanding is that field rotation only occurs when you are guiding, as it's a function of guide star angle as per this. 

I suspect you are talking about declination drift.

Declination drift? Like you mean, I wasn't perfectly aligned it right, or it wasn't perfect?

Declination drift is the drift that happens if you are not perfectly polar aligned and if you are not guiding. 

You mentioned that you got within 0.9 and 0.3 degrees of alignment. This is still pretty far off alignment, at least from my experience. With my 1.4"/px setup, I make to sure to get within 1 arcminute, for reference.

So like how careful you need to be to achieve this to be perfect, I saw in a video that someone showed how to do a perfect polar alignment where both values were 0. I use the th10 tripod head cause it looks like it can do a smoother polar alignment than a wedge it has. So just wondering how I can do that without moving too much.
Tony Gondola avatar
Tony Gondola avatar
Oscar:
Szijártó Áron:
were 0.9 and 0.3


@Tony Gondola these PA numbers are in degrees btw

.9 degrees is pretty loose so you will certainly get trailing with longer exposures.
Craig Rairdin avatar
Craig Rairdin avatar
Noah Tingey:
Are you sure that it was field rotation? My understanding is that field rotation only occurs when you are guiding, as it's a function of guide star angle as per this. 

I suspect you are talking about declination drift.

I can't follow your link for security reasons but yes, I'm talking about field rotation. Equatorial mounts are superior to alt-az mounts specifically because they eliminate field rotation. OP was (correctly) expecting that his star trails problem would be eliminated by using an eq wedge and putting the Seestar in eq mode and was disappointed that it did not. I was pointing out that there can still be star trails from other causes, including bad polar alignment and the tripod not being level as others had pointed out. My whole point was to say that there are many causes for star trails. Eq mode eliminates field rotation as a cause, but doesn't eliminate all causes.
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Szijártó Áron avatar
Szijártó Áron avatar
Tony Gondola:
Oscar:
Szijártó Áron:
were 0.9 and 0.3


@Tony Gondola these PA numbers are in degrees btw

.9 degrees is pretty loose so you will certainly get trailing with longer exposures.

Ah, that explains it. For a moment, when the seastar hit these values, I said okay, it looks like this also works, but 5 seconds ago, the altitude value moved away even though I didn't touch it. So I wonder how close I can go to achieving the polar alignment perfectly, cause if I move it too quickly, I just will screw up the setup.
Tony Gondola avatar
Tony Gondola avatar
Szijártó Áron:
Tony Gondola:
Oscar:
Szijártó Áron:
were 0.9 and 0.3


@Tony Gondola these PA numbers are in degrees btw

.9 degrees is pretty loose so you will certainly get trailing with longer exposures.

Ah, that explains it. For a moment, when the seastar hit these values, I said okay, it looks like this also works, but 5 seconds ago, the altitude value moved away even though I didn't touch it. So I wonder how close I can go to achieving the polar alignment perfectly, cause if I move it too quickly, I just will screw up the setup.

Well I don't know how fine the adjustments are but you should be able to do better than almost the width of two full moons. The whole setup needs to be beefier and better balanced, all on a solid, level base. The needed accuracy is rather tight and once there can't be allowed to shift because of slewing, winds or tripod slop.