Star Tracker alignment

Started 3 months ago | Questions
vbuhay
vbuhay Veteran Member • Posts: 4,364
Star Tracker alignment
1

I just recently purchased the Star Adventurer 2i, and did my first Polaris alignment this weekend. My question is , is there a way to do an alignment without using the the polaris method. I want to be able to use my tracker without seeing Polaris. I live in an apartment in the city and do not have a view of the Polaris.... the only way to align with Polaris is to drive a few hours to get a dark enough skies...

Thank you in advance....

ist Milkyway with a tracker...

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W5JCK
W5JCK Veteran Member • Posts: 3,730
Re: Star Tracker alignment
1

If you are going to use it for UWA or WA shots then you can do a rough, estimated alignment. The wider FLs don't require as much precision in the alignment. Here is what I do:

Use a compass to find true north. Orient the tracker towards true north. Elevate the tracker the same number of degrees as your latitude. For example, if you live at latitude 32.5° N, then elevate the tilt angle of the tracker to 32.5°.

That should get you close enough to take longer exposures with a FL up to 50mm (on a FF camera). I routinely get 30 sec shots at 50mm on my FF using this method. It works better for wider FLs of course. It won't work for telephoto though.

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vbuhay
OP vbuhay Veteran Member • Posts: 4,364
Re: Star Tracker alignment

W5JCK wrote:

If you are going to use it for UWA or WA shots then you can do a rough, estimated alignment. The wider FLs don't require as much precision in the alignment. Here is what I do:

Use a compass to find true north. Orient the tracker towards true north. Elevate the tracker the same number of degrees as your latitude. For example, if you live at latitude 32.5° N, then elevate the tilt angle of the tracker to 32.5°.

That should get you close enough to take longer exposures with a FL up to 50mm (on a FF camera). I routinely get 30 sec shots at 50mm on my FF using this method. It works better for wider FLs of course. It won't work for telephoto though.

Thanks Jack,

I am actually tracking the moon using a Tamron 600mm lens and using my rough compass and latitude of 33 deg give or take... it sort of works since my SS is in the 1/600 sec. range for the moon only, but when I try to get longer exposure to get the stars it gets a bit Blurry...

I am trying to get the moon with stars in the background.... might have to do a composite instead...

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W5JCK
W5JCK Veteran Member • Posts: 3,730
Re: Star Tracker alignment

The ballpark alignment, which is what a I call it, will help some for telephoto at 600mm, but probably not much. I can get up to 8 sec at 400mm if I’m really lucky, but usually less. It is close enough to keep me from having to constantly readjust the camera to keep the Moon in the FoV, so that helps.

To get the Moon and stars when the Moon is a crescent, you might need a bit more shutter time. But if you can get a good alignment, you can take several exposures at various exposure levels to create an HDR image. If the Moon is too bright though, it will wash out the stars.

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Kazmarov Contributing Member • Posts: 983
Re: Star Tracker alignment

Drift Alignment is an option to consider.

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hha Contributing Member • Posts: 661
Re: Star Tracker alignment

vbuhay wrote:

I just recently purchased the Star Adventurer 2i, and did my first Polaris alignment this weekend. My question is , is there a way to do an alignment without using the the polaris method. I want to be able to use my tracker without seeing Polaris. I live in an apartment in the city and do not have a view of the Polaris.... the only way to align with Polaris is to drive a few hours to get a dark enough skies...

vbuhay:

As others have pointed out, alignment with a compass is an option. With a high quality compass and inclinometer, and a lot of practice, I typically find Polaris within one degree of the center of the pole axis scope on my IOptron Skytracker. If I stop there, how good is that?

Shown below is a picture of M13 taken with the Nikon Z6 with a f=135mm lens at f/4 from my backyard. This is 522x448 pixel cropped from the 4000x6000 image.

The Skytracker was allowed to run unattended for 3 hours. The resulting 174 x 1 min images were registered on the stars with Sequator, without using dark frames. The star registration is very good. The faintest stars are 2x2 pixels. Since my polar alignment was only approximate, hot pixels are visible as 140 pixel long trails. The slight curvature is due to flexing  of the setup. The 3 pixel wiggle in the trail is the 27” worm error of the Skytracker with a 9 minute period. The trails due to polar misalignment were a fraction of a pixel per one minute exposure.

The pole axis alignment was close to 0.5 degree off. That is the answer to how close you alignment has to be with 1 minute subs and 135mm lens using a 24 Mp camera. With a shorted focal length or shorter subs you could be even more off and still get excellent results.

By the way, when the data is processed with darks, then the hot pixel trails disappear, and you would not know how sloppy the polar alignment was.

Cheers.

hha

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Astrophotographer 10 Forum Pro • Posts: 13,907
Re: Star Tracker alignment
1

I use some smartphone apps. I set south (I am in the Southern Hemisphere) using the compass app. It seems quite accurate and I don't think its affected too much by the metal in the tripod or camera.

I set the angle using a digital inclinometer free app to my local latitude.

That gives me round stars 30 seconds at 14-21mm.

Greg.

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ErnieG530 Regular Member • Posts: 101
Re: Star Tracker alignment
1

You can find videos on YouTube.com  about this. Do a search on "align without Polaris". These will help, Dark Skies, Ernie

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