Mauna Kea (Hawaii) Astrophotography advice?

Started Sep 27, 2017 | Discussions thread
Astrophotographer 10 Forum Pro • Posts: 11,467
Re: Mauna Kea (Hawaii) Astrophotography advice?

deednets wrote:

Astrophotographer 10 wrote:

deednets wrote:

I rarely ever do this but will bookmark this post. Fabulous!!!

Now, regarding the Vixen Polarie, I have now and again played with the idea of getting 9ne, but must say that I wouldn’t know how to set it up.

In short: how “easy” is easy??

Thanks

Deed

Hi Deed,

You're in NZ right? So you need to polar align to the south celestial pole.That is the point in the sky that all the stars rotate around.

You can roughly align the Polarie simply by getting one of their accessories that fits on the hot shoe on top and has an inclinometer which shows the angle the Polarie is set to and a compass. The angle is the same as the latitude of where you are. For example at my dark site its 33 degrees south so the Polarie has a little angle dial on its side and I set the angle of the Polarie on the tripod to 33 degrees. Now it has to point due south.

The compass give an idea but of course there is magnetic south and actual south. So you need to know the offset for the 2.

I use the Polar scope. Its a little telescope that fits through the hole in the Polarie.

You need to find a trapezium of stars around the star Octans. There is a bright star next to the large magellanic cloud. Start there. Now right near it are 3 fairly dim stars that form an arrow shape. That arrow is pointing towards the Trapezium stars which are about 1.5 screens away. Move the unit gently and smoothly and don't loosen the controls of your tripod. I use a Manfrotto tripod which has arms that control the rotation and angle etc. I don't loosen them too much just enough to be able to move it slowly without it suddenly dropping.

The polar alignment scope has an etched reticle in it. When that is illuminated with a dim red torch you can see the Trapezium formation etched into the reticle. You find the Trapezium as above and then line it up with the reticle and once they overlay you lock off your tripod and you are done. Now you will find you can do up to 15minutes at 14mm.

I used to find shining a torch down the polar scope very hard. It would be too bright and dazzle my vision. I would wrap a dim torch with a rag to dim it down even more so I could see both the stars and the reticle. It was hard.

I found an accessory meant for a Skywatcher polar scope which is an illuminator. It attaches on the end of the polar alignment scope and you can control its brightness. The stars get overwhelmed easily so you don't have it very bright, just enough to see the stars and the reticule so you can make them overlap.

I also use a USB power pack to run the Polarie which seems to last for ages. The unit uses 2 AA batteries but I find they run out very quickly. I have the USB power pack attached to the tripod using Velcro.

In the northern hemisphere they merely have to align the scope with Polaris (the north star). All very quick and simple so they have it easier.

It helps if you know where the south celestial pole more or less is.

If you are looking south at a dark site you will see 2 white patches. Those are the Magellanic Clouds which are 2 of the companion galaxies of the Milky Way and they orbit our galaxy. Now off to the other side that they are on you will see the pointers of the Southern Cross. if you criss cross lines from the pointers and the Magellanic clouds where they intersect is pretty close to the south celestial pole. I have sometimes simply looked for the Trapezium stars by pointing at where I know roughly the pole is. That works but it would be hard for the first few times until you can recognise this Trapezium. That takes practice.

https://www.vixen.co.jp/en/polarie/polarie_movie.html

Greg.

Oh boy ... not "easy" as such right??

But thanks for trying!!! Maybe into the too-hard-basket she goes??

Deed

Don't be a baby Deed  Mate,I thought you were a tough Kiwi. hehe

Yes, its a bit daunting the way I put it but just go the easiest to start and have some fun and some decent images with it. Simply setting it at the angle of your latitude is simple as it has a tilt meter built into its side and then point it roughly where south and you will get a big improvement in your stars. To get it perfect requires the above so leave that to another day after you've had a lot of fun.

I develop another technique that is "fairly simple".

1. Set the Polarie to the angle which is your latitude using the tiltmeter on the side of the Polarie and a torch so you can see it.

2. Point to where you think south is (between the Magellanic clouds and the Southern Cross).

3. Focus your camera and do a 30 second exposure at ISO6400 F2.8.

4. Look at the image with magnified view - are the stars round or elongated? How are they better than  untracked images?

5. If elongated leave the angle unchanged as that is going to be quite close. But the pointing south is off. So rotate the Polarie one way or the other (your best guess0. Take another exposure. Are the stars better or worse? If better then you rotated the Polarie the right way. If its worse you went the wrong way. So if worse then rotate the Polarie back to where you started and then a bit further. Take another exposure, is it better or worse and continue until you are happy with the results.

6. This can be done fairly fast as really if you only taking 30 seconds shots with a wide angle lens there is already a lot of tolerance. Getting round stars in 30 seconds 12-14mm lens shots is not very demanding of the Polarie at all.

Greg.

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