So I’ve finally been getting a bit of use out of Move Shoot Move 2-in-1 Star Tracker & Rotator for actual star tracking sessions of late. I’ve used the rotator function of this device extensively, a function that to my mind almost justifies the cost of this device on its own merit. The star tracker however wasn’t quite working for me. With Australia being in the Southern Hemisphere, I had no bright pole star to align too even if the star pointer laser was legal. I went with the polar scope option with my purchase, however simply could not positively identify Sigma Octantis, the tiny magnitude 5.5 pole star for the Southern Hemisphere, through the scope no matter how hard I tried. I retired myself to the idea that I was going to have to make do with blind alignment using apps on my phone for a “near enough” polar alignment for which only wide focal lengths could be used without trails. To date, I have been quite pleased with how wrong I’ve been about this.
I recently treated myself to a new Sony 20mm f/1.8 lens which has replaced both the Sigma 20mm f/1.4 and Samyang 24mm f/1.4 in my camera bag. During the week I made use of some clear skies and decided to get this new lens onto my Sony A7R and have a go at some Milky Way shots from the deck at my house in Bortle 5 suburbia. After getting my blind alignment honed in I started increasing the exposure time on my A7R looking for the point at which stars trails appeared. They didn’t come. I incremented the exposure time by a minute at a time until I had the exposure at 5 minutes at which point I was able to capture the following.
There was no point increasing the exposure further as the image histogram, although quite narrow, was well into the middle of the range. I decided to see what I could get using a longer focal length. As I do not currently have any long focal length full frame lenses for my Sony cameras at present, I decided to get my Panasonic GX85 Micro Four Thirds camera a go with the awesomely sharp Olympus 75mm f/1.8 prime lens. Given the 2x crop factor of the Micro Four Thirds format, this was an equivalent of a 150mm lens on a Full Frame camera.
I was not expecting much as the Micro Four Thirds format in general is not known for very good low light performance with the exception of a few stand out examples such as the Panasonic GH5s and Black Magic Pocket Cinema Camera 4k. The lack of low light performance impacting the GX85 even more so as it uses an older 16MP sensor where the more modern Micro Four Third cameras are using a better performing 20MP sensor. Given the lack of a remote port or BULB function, I was also limited by the maximum exposure time of 60 seconds. I completed a test shot an was pretty amazed with what I saw on the screen. No discernible star trails…….at a 150mm FUll Frame equivalent focal length…. on a tracker polar aligned using nothing but apps on my phone.
I quickly learnt that composing an image at this focal length using nothing but a ball-head mount has its limitation. I locked in on the great rift as best I could and using the built in time-lapse feature of the GX85 set it up to take 10 x 1 minute exposures. Processed through RawTherapee, stacked for noise reduction in Sequator and finally touched up in Affinity photo I was quite pleased with the end result.
I already had a high opinion of this Olympus lens, this just took that to a new level. Zoomed in at 200% on the full 36MP raw file I can see some slight elongation of the stars, it is very slight though and given the polar alignment technique and focal length I’m more that happy with the result. I feel I will be exploring this blind alignment technique more closely in the coming months.