I have always been an avid landscape and wildlife photographer however, over the past four or five years my photography has gradually become devoted to “Astro Photography”. In my case, I prefer to call this type of photography “Starry Landscapes”.
Astrophotography involves lots of advanced planning such as where certain heavenly bodies will be positioned for the landscape, will the moon be present in the sky, etc., etc., on certain nights of the year. This is carried out in a wonderfully useful App called Photopills. The biggest problem in the UK is whether the sky will be clear on the nights of the planned photographs.
When photographing landscape and stars in the middle of the night, the most important consideration is the light-gathering power of the lens. For this reason, many of the wide aperture Sigma Art lenses are widely used for Astro Photography. Probably the most popular Sigma Art lens is the superb 14mm f1.8 lens which I love using.
In Astrophotography the main aim is to display the stars as sharp pinpoint objects. This dictates how long the exposure can be and therefore the maximum shutter speed. The maximum shutter speed depends upon the focal length of the lens. The more wide-angle the lens the longer the possible shutter speed. With a 14mm lens, it is possible to use shutter speeds as long as 20-25 seconds. But unfortunately, with a 50mm lens, the maximum shutter speed becomes shortened to 5 or 6 seconds. For this reason, the 14mm lens is the most widely used lens for Astro Photography.
Unfortunately, not all lenses are not suitable for Astro Photography. Many lenses that are superb for normal daylight photography, often prove to be unsuitable for Astro Photography, when used at wide apertures. They are frequently prone to “Coma Distortion” which only becomes evident when subjects like stars are photographed. Coma distortion makes pinpoint stars appear elongated with winglike shapes!! This usually appears in the corners of the frames, spoiling Astro images. This distortion normally decreases as the lens is stopped down. In the case of the Sigma Art 14mm f1.8 lens, the coma distortions only slight, wide open, but has disappeared by f2.5 making it a great Astro lens.
Unfortunately, a 14mm lens is so wide that it fills the frame with massive amounts of sky and landscape, sometimes displaying far more than I would really like in all images. For this reason, I frequently use a 24mm lens. For many shots, even the 24mm lens gathers more of the landscape than I would really like and so I sometimes want to crop the image to a size more appropriate to that of a 35mm lens.
This finally brings me to why I am so thrilled with my new SIGMA 35mm F1.2 DG DN | Art lens.
At a focal length of 35mm the maximum shutter speed that I can use only 8 seconds which means that with a lesser lens I would be shooting at around f2.8, (to exclude coma) and using an ISO of 6400 – 10000!! When I read the description of the SIGMA 35mm | Art lens it claimed that the lens was virtually distortion-free, WIDE OPEN.
When I received the lens, on the first clear starry night I went out to test the lens for coma, at various apertures. I was blown away by the results. Even wide open at f1.2, there was hardly any coma distortion. At f1.2 only a tiny amount of coma could be detected in the extreme corners, when the image was magnified to 200%, in Adobe Lightroom. On stopping the lens down to f1.4 any hint of coma had totally disappeared. This means that I can use the lens for 8-second exposures at f1.4 and reduce my ISO values to ISO 1600 to ISO 3200! This gives me a massive advantage with this lens, at least 2 stops better than the best 35mm lenses.
I have only had the lens a short time but I seem to have settled into using the lens at apertures between f1.8 and f2.2 as I get marginally more depth of field at these apertures than at f1.2. When including closer objects such as the stones of Avebury or Stonehenge, I usually take a further exposure at f4 and with a longer shutter speed, to obtain sufficient depth of field to render the foreground sharp. This second image is then blended with the main exposure, using masks in Photoshop, to obtain sharpness throughout the image.
In a few words, this SIGMA 35mm F1.2 DG DN | Art lens has revolutionised my Astro Photography. I’m sure that it will soon become a regular part of my daytime camera bag!! It is a winner.