The southern-most part of the our Milky Way galaxy taken from about 34 degrees
south of the equator on a remote Karoo farm near Prince Albert, South Africa
Tripod mounted Canon EOS 1DX with Canon EF 24-70mm f/2.8L IS lens @38mm. ISO 3200.
Evaluative metering, EC =+1 2/3 stop: 13 sec at f/2.8 using live view mode to manually focus and a remote shutter release chord.
Weltevrede Fig and Guest Farm
When we decided to visit this farm for a few days, I immediately thought of the wonderful opportunity to capture some images of the night sky. The farm is 25 km from Prince Albert, and being without electricity, provided the ideal conditions for some astro-photography. January is a particularly hot month for this part of the country with the daytime temperatures in the high thirties and one day touching the 40 degree (celsius) mark. However, the moon phase was about three quarters to full moon – a waxing gibbous – so this entailed getting up at 02:30 in the morning to ensure a dark sky unlit by the moon.
The farm itself is a working fruit farm with figs and peaches being the main products. It is remotely situated about 25 kilometres west of Prince Albert, accessed on a very good gravel road that ends at the farm. There are a number of guest cottages located at various points on the farm. We stayed in the “de Hoek” cottage – a very comfortable house with a much-needed swimming pool. The days were extremely hot (as were the nights) so not much activity was possible in the middle part of the day. The surrounding scenery was special as can be seen from this view towards the mountains at the back of the farm. This image was captured on the morning we left and that was the only time we saw any sign of a cloud!
Equipment needed for the star images
A wider angle lens is a pre-requisite in order to capture a meaningful section of the sky. To obtain larger sections of the sky a very wide angle lens is required or a number of images can be captured as a panoramic combination. The widest I have is the 24-70mm f/2.8L IS lens which proved adequate. A sturdy tripod and a remote shutter release chord were essential. I used the Canon EOS 1DX body as it is a full frame sensor body and it has excellent high ISO performance. You will see why this is necessary! A torch and headlamp were most useful to see what you were doing – to say nothing about looking out for snakes.
The images that I wanted to capture were not star trail pictures – I wanted the stars to be stationary rather than elongated streaks of light. This meant that the shutter speed could not be too long as this would result in “streaking” and if too short there would not be enough light captured to highlight the millions of stars.
Remember that we are travelling pretty quickly on the surface of the earth in relation to the heavens. At the equator the earth is spinning at a tangential speed of 1674 km/hr which translates into 465 meters per second. As you move further away from the equator the speed decreases. The farm was about 34 degrees south of the equator so the surface speed was 386 meters/sec (cosine of 34° × equatorial speed). There is a fair amount of mathematics necessary to calculate the slowest shutter speed that would result in the stars not showing movement. The time required will depend on the speed of a star across the sensor, so the factors would be pixel size on the sensor, radial speed and focal length. This results in a good rule of thumb that the shutter speed should not be slower than 600 ÷ focal length (at or near equator). Factoring in 34 ° S, this translates to about 500 ÷ focal length. As I used a focal length of 38 mm the shutter speed should not be slower than 13 seconds. Using 13 sec as a shutter speed and an aperture (wide open for the lens used) of f/2.8, exposure was about optimum at an ISO of 4000. I decided to go for a slightly lower ISO of 3200. The correction could be made in the post processing by increasing the brightness by about a half stop.
Focus is difficult as the DOF is very shallow. Live View helped as you can enlarge the image on the back LCD screen and get a more accurate focus of the stars.
The Southern Cross is synonymous with the southern sky, so that was an obvious portion of the sky to photograph. A protruding tree branch was composed into the image to give it some earthly reality. In the centre of the featured image the pointers to the Southern Cross can be clearly seen in a vertical position. The pointers are Alpha Centauri (the bottom star) which is bright white, whilst Beta Centauri (the top star) is more bluish. The actual Southern Cross formation is about two thirds up the image and slightly right of centre. The major axis is about at a 10 to 4 (clock time) position. Depending on your screen resolution and quality, the stars at the foot of the cross and at the ends of the cross bar are blue-white, and the Gamma Crux at the top of the cross appears as an orange star. The Coal Sack is the dark shape just beneath the cross. This is a region of gas and dust, known as a dark nebula, which obscures light from the stars behind it. Just below Beta Crux ( the left hand side star of the cross bar) the Jewel Box is visible as a small grouping of stars.
This is a most interesting part of the milky way. In the right side top corner of the featured image is a large cluster of very bright stars varying in colour from white to blue to reddish mauve. The grouping of stars is an open cluster in the constellation of Carina and is commonly called the Wishing Well Cluster (astronomical name NGC 3532) because through a telescope it looks like dozens of silver coins twinkling at the bottom of a wishing well. NG3532 was the first target ever observed by the Hubble Space Telescope on May 20, 1990.
At about a 5 o’ clock position to this bright cluster is another cluster of bright blue stars – the Southern Pleiades, also part of the constellation Carina.
View into the valley with the farm in the distant background.