Review of the Vixen Polarie star tracker

Review of the Vixen Polarie star tracker

You’ve seen those awesome wide-angle Milky Way photos, sometimes with a building or a tree in the foreground. They’re great, right? Want to take one yourself? I’ve taken a few in my time, but never really nailed it. Star trails look nice, but if you don’t want them, it’s awful. The Vixen Polarie can help with that.

The Vixen Polarie is a compact and light star tracking device. It enables you to take photos of the sky using a DSLR camera and a lens. The Polarie rotates the camera to counteract the Earth’s spin. This means your photo won’t have star trails. Put simply, it’s a very light equatorial mount, although its designers have tried their utmost to make it look anything like one.

We got a Vixen Polarie to review, and after a few tests, I took a fairly successful photo of the Large Magellanic Cloud. Here it is, and this is the story of how I did it.

Large Magellanic Cloud, stack of 114 60s exposures using Vixen Polarie

Overall verdict

The Vixen Polarie is easy to use and pretty easy to set up and roughly align. By that I mean good enough to get exposures of a minute or so. I found, though, that setting it up more accurately was a challenge.

The unit is small enough for you to take with you anywhere – it’s not quite pocket-sized, but it’s certainly hand-luggage sized. Having said that, it does need a heavy-duty tripod to keep it stable.

If you use a short focal length lens on your camera it will enable you to take remarkable wide field photos of the Milky Way and other targets. But it you use a longer lens or a small telescope, the alignment becomes more critical. It’s even more of a problem in the Southern Hemisphere, where we are.

However, I can see myself falling in love with this little jigger, despite it’s being fiddly. Those wide field photos are great, and the step-up from tripod-only shots is very noticeable.

What you get

The basic unit ships on its own, or as a package which includes a tripod and a ball head as well. The ball head allows the camera to swivel to any target, so to take photos away from the equator you obviously need this. However, any heavy-duty tripod (with the standard ¼” thread) will work with the Polarie.

I found it a little curious that the basic unit comes without the ball head, but instead, the ball head comes with the tripod. It would have made more sense to me to have the ball head packaged with the basic unit and the tripod sold separately, as you can’t really use the unit without the ball head.

Ball head for the Vixen Polarie

The unit also runs on a couple of AA batteries, or you can power it using an USB input (which is 5V). One tip though: you have to bring spare batteries. Mine lasted less than two nights. They’re easy to change, though, because they’re under a large panel on the side. You don’t need to take the camera off the Polarie, or the Polarie off the tripod in order to change them.

The unit itself

The complete Built-in compass and polar alignment hole on the Vixen Polarie assembly on a tripod

Design

The Vixen Polarie is quite heavy in your hand. It feels solid and well made.

The Vixen Polarie sits nicely in your hand

The overall shape of the Vixen Polarie is reminiscent of a camera. My guess is that they designed it like that because it’s pitched to photographers rather than astronomers. Its main competitor looks much more like an equatorial mount, which, to some non-astronomers, can be intimidating.

While operating this piece of equipment accurately does take some practice and knowledge, it’s not that difficult. If you can use a DSLR to anything more than point-and-shoot level, you can easily learn to use a star tracker.

Settings

The Polarie’s dial has five settings (apart from “off”, of course).

For alignment in the dark, there is a mode that simply illuminates the latitude dial. This helps when aligning, especially if you’re on a photographic field where torches are banned.

Sidereal tracking is marked with a star. This is the most common mode and simply tracks at a rate that keeps up with the stars.

Vixen has had the idea of a half-sidereal rate. This helps you get an astroterrestrial photo with stars in the background and a tree or building as a foreground subject. The half sidereal speed shares the motion blur between the foreground and the background. This compromise will get you longer exposures. Depending on your focal length, you might get a minute or even more.

The other rates are lunar and solar tracking. I’m not convinced these are useful, as there isn’t a great difference between these rates and the sidereal rate. To make them necessary you would have to have exceptional polar alignment.

Capacity

The Polarie is designed as a portable tracker. It can support a camera and lens of up to 2kg. In comparison, its main competitor can carry up to 5kg. However, the Polarie doesn’t need to support a heavy telephoto lens. The type of photo people use the Polarie for is a wide-angle skyscape, not a narrow field shot. Wide field photos use shorter focal length lenses which are much lighter.

Setting it up

Putting it together

The Polarie has a silver circular plate (they call it a “camera mounting block”) on the front. Two thumb screws secure it to the Polarie’s axle. You remove the plate by loosening the thumb screws. Push the spring-loaded button at the back of the plate to reveal a standard ¼” thread.

Thread on Vixen Polarie's camera mounting block

Attach the ball head here, and then put the camera mounting block back onto the Polarie.

Ball head and camera mounting block on the Built-in compass and polar alignment hole on the Vixen Polarie

Next, attach the Polarie with the ball head to a standard tripod. Then you attach your camera to the ball head. This is the final assembly.

Vixen Polarie assembled with ball head and DSLR

Here’s one thing to watch out for. While I was setting mine up there was a sudden failure. The camera fell and hit the tripod head. There wasn’t any damage, though. It seems I hadn’t screwed the ball head to the camera mounting block tightly enough. I’d tried to avoid over-tightening as I didn’t want to scratch any of the parts. I tightened the ball head a bit more and it didn’t happen again. When the camera was on the westward side of the Polarie, this exerted an anti-clockwise pressure on the ball head. I was a bit more careful when the camera was in this position.

Aligning it

The whole point of the Polarie is to counteract the apparent motion of the stars. To do this, the Polarie rotates around an axis pointing at the South Celestial Pole (SCP).

This is a hand-scribbled diagram that shows what I’m talking about. The Earth rotates one way, and the Polarie rotates back the other way, leaving your camera dead still.

Equatorial mount diagram

The more accurate you can get the Polarie aligned to the pole, the better it will track. With more accurate tracking, you can take longer exposures.

Polar alignment has long been a bugbear of astrophotographers, especially in the Southern Hemisphere. You can align the Polarie in a number of different ways. However, there is no method that’s simultaneously easy to use and especially accurate in the Southern Hemisphere. You just need practice.

First, the Polarie has a small viewing hole at the top right of the back. This is simply a hole straight through the unit. The designers intend you to look through it to the stars beyond. In the Northern Hemisphere, where there is a bright star near the pole, this might be useful. However, it’s pretty useless in the Southern Hemisphere. It’s difficult to find a dark patch of sky and differentiate that from the adjacent dark patch. In the dark it’s awkward to peer though the hole. What’s more, it’s hard to know if you’re looking straight through it or not.

Polar scope

As an accessory, Vixen (and other third parties) sell a polar scope with a reticule. This reticule is a screen you can look through that shows where the alignment stars should be. You install the scope through the centre of the Polarie, then peer though it to align on Sigma Octantis. In the best conditions, this is a very accurate way of aligning the Polarie. The problem is that finding Sigma Octantis in a polar scope is famously difficult. It’s even harder in a light polluted area.

Having polar aligned with a scope, you then have to remove the scope, replace the rear cover on the Polarie, attach the camera mounting block with the ball head and camera, all without moving the Polarie. Move it a fraction and you’ve lost polar alignment and you have to start over. This would be a horrible bummer.

More please?

Something else that would be useful would be a red dot finder that sits on the flash shoe on top of the Polarie. Correctly aligned, this would make aligning the Polarie a little easier, and would certainly be less awkward than looking through the polar viewing hole. You would use the same red dot to aim the camera after aligning the Polarie. They’re available, and not terribly expensive.

This is what I did

Built-in compass and polar alignment hole on the Vixen Polarie

Without accessories, you can roughly align the Polarie using the built-in compass and latitude (or “altitude”) meter.

Vixen Polarie's altitude gauge

This is what I did on my first night. The whole alignment only took me a minute or so. I found it to be accurate enough, as I was able to get 30 second exposures with round stars. Having a bit of experience in polar aligning, I’m also good at finding Sigma Octantis with binoculars. Doing this first makes things a lot easier, as it gives you a head start finding true, not magnetic, South. This is a quick procedure, and you can do it all with your camera on the Polarie.

On my second night, I tried something a little more complex. During the afternoon, I used a GPS to find a point on the other side of the viewing field due south of the camera. Then I pointed the Polarie in that direction before using the latitude meter to tilt to the right angle.

Photos

Enough about the unit itself, let’s get onto the interesting stuff. The results.

Test photos – and a short animation

On the first night I used the Polarie I set up in back yard in suburban Melbourne. There had been some extensive bushfires that week and the light pollution was terrible. It’s OK, this was really just a test.

I set the Polarie up on the grass and pointed it due south. I have a mark on the fence so this was quite simple. Then I used the gauge to set the altitude. The gauge is small but appears to be reasonably accurate. I needed about 37.8°, and the photo looks closer to 36. The results showed that that was probably close enough for a 30 second exposure when using a 28mm lens.

Polarie set up in my back yard

Before I launched on the sequence of exposures, I did a few tests to see if the Polarie was working. This also helped me get the exposure right. I didn’t have high expectations due to the smoke haze.

These two 15 second exposures are of the same part of the sky. They show the difference between when I had the Polarie running and when it was off. It’s pretty clear that the Polarie stopped most of the apparent motion of the stars. The ones on the right are much more pleasing dots.

Test 15 second exposures with and without Vixen Polarie running

Go!

I satisfied myself that the Polarie was running, as it makes a quiet clicking sound. Then I plugged in my intervalometer and programmed a sequence of exposures. I wanted 65 30 second exposures every two minutes. I pointed the camera at where Orion was (even though at that stage it was behind a tree) and pressed go. Then I went to bed for a couple of hours.

This is a detail from one of the images I got. It’s a bit noisy, but you can see the three belt stars. The Great Nebula is at the top.

M42 taken using a Vixen Polarie

I turned the resulting sequence of images into a very short animation which you can see on the Optics Central YouTube channel. In the animation, the horizon falls away to the right, revealing Orion in a heavily light-polluted sky.

The sequence also shows that my polar alignment was not perfect. The stars in the East appeared to drift northwards. Better polar alignment would stop this.

My second photo

A week or so later, I went up to the Astronomical Society of Victoria’s Dark Sky Site. This is a wonderful resource for members of the ASV. I used an old Pentax SMC 85mm f/1.9 screw mount in my Pentax K3-II on the Polarie. I thought the Large Magellenic Cloud would make a good target.

Setting up the Polarie using my GPS to find true south, I tried to find the LMC. Several minutes of pretty intense gymnastics later I succeeded. I’d pointed the camera in the right direction and focused it. I set the intervalometer to record 60 second exposures every two minutes. This gap between exposures allows the sensor to cool and avoid noise build-up. The sequence lasted about four hours. While it was clicking away to itself, I took a reasonable photo of the Horsehead nebula.

Individual images

This photo is the first of the sequence, completely unprocessed. It shows the field of the 85mm lens, as well as how dark the individual photos are. This really shows the benefits of digital stacking software.

If you look closely, you’ll see the stars in the centre of the field are nice and round. However, in the corners they have been elongated away from the centre. This is a problem of the lens, and not the Polarie.

Single uncropped 60s exposure

Over the course of the sequence, it became apparent that my polar alignment was not perfect. It was good enough for a 60 second exposure, but over four hours the LMC had drifted away. Again, aligning the Polarie accurately had been a challenge. It looked like I hadn’t been able to do it as accurately as I’d hoped.

Processing

Taking the raw images home, I stacked and processed them (including some calibration frames) in Astro Pixel Processor. I could have used Deep Sky Stacker, or any number of other packages. Stacking images is a way of increasing the signal to noise ratio of the individual frames to allow further processing. I finished the image off with Photoshop. I cropped the stacked image to keep the LMC in the centre of the frame.

The final image is at the top of this blog. I am pretty happy with the way it turned out, especially as it was only my second go at the Polarie.

What would I do for next time?

Plan, do, review. Whenever I do anything new, it’s natural to want to improve. So, what were the lessons for next time?

First, I would want better polar alignment. Each exposure had good round stars (at least as good as the lens was capable of). However, over a long sequence it drifted in the frame so I nearly lost my target. I think this would take some practice.

Second, it’s a pity I didn’t have the Milky Way available. MW shots are brilliant, and to get a really good image would be great. I’ll have to be patient, as MW season is over.

Third, a red dot on a flash shoe would make things easier, both for alignment and for aiming the camera. They’re not expensive.

Fourth, I’d like to try a wider lens. I used a 28mm for the Orion sequence, and this might be better than the 85mm.

The bottom line

There are so many targets and lenses. The Vixen Polarie can open up an entirely new level of wide field astrophotography. This (along with my telescope and other equipment) could keep me interested forever.

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