The Sigma 35mm Art is renowned for its sharpness and the Sigma Art series lenses are supposed to be some of the best on the market. I purchased this lens back in 2015, hoping it would make an excellent lens for Milky Way photography, with its f/1.4 aperture. On my 2016 roadtrip, I was able to capture some stunning Milky Way photos with the Sigma!
Great Sand DunesThe Milky Way, as seen from Great Sand Dunes National Park
Oddly enough, I never got around to testing the Sigma's performance until my recent trip to Cherry Springs. I wanted to see just how bad the coma really was. For these tests I set the camera to an 8 second exposure, following the 300 Rule for sharp stars. I changed the aperture from f/1.4, f/1.8, f/2, f/2.8 in each subsequent photo.
I was really surprised to see how well the lens performed at f/2.8 compared to the other aperture values. It's almost like a completely different lens! The slideshow below shows each aperture value. Notice how the vignette disappears at f/2.8. Mobile users can click here to see the gallery.
The vignette can be easily corrected by stopping down. Alternatively, you can use the built-in Lens Correction Profile in Adobe Camera RAW to remove the vignette. After applying the profile corrections, each image looked virtually identical.
Coma is always a major concern for any lens at night. Instead of having pin-point sharp stars, they appear to grow wings. This can usually be fixed by stopping-down. Personally, if I have a lens that can open up to f/1.4, I want to use it there! More light is always better when photographing at night. The slideshow below shows 2 coma examples. One was a very heavy crop to the right corner of the image. The other was a heavy crop near the center. Click here to visit the Coma Gallery.
At f/1.4 the coma is pretty bad even in the center of the image; none of the stars are really sharp. It took until f/2.8 for the coma to disappear entirely. Another thing you'll notice is how much noisier the image becomes as the lens is stopped down. As the aperture changes from f/1.4 to f/2.8, there is a loss of 4 times the amount of light!! Now you can see why I want to use this lens at f/1.4 as much as possible!
The Sigma 35mm Art can capture an extraordinary amount of light when opened up to f/1.4. This will allow you to capture tons of detail in the Milky Way and substantially reduce the amount of grain. However, the coma performance is pretty bad. To be honest though, most people aren't going to notice the image grain or coma! They will notice the composition and colors though.
There are a couple different routes you could go. Set the camera to f/2.8 and take multiple photos (20+). This process is called Photo Stacking and will remove the grain from the photo. You will need Photoshop to do this. You can watch my full YouTube tutorial on this process for more information. This method will allow for sharp stars, no vignette, and a grain-free image!
Or, if you don't want to spend 20+ minutes editing one photo, you can simply set the aperture to f/1.4. The stars will show coma, but again, most people will never notice or care! The photos taken at f/1.4 will be considerably cleaner, as more light is able to reach the sensor.
Finally, you can buy a star tracker and set the camera to f/2.8. The star tracker will move at the same speed as Earth's rotation, allowing you to take much longer photos. If you set it up correctly, you can shoot a single exposure for well over 1 minute without any blur in the stars! Of course, you would then need to blend a static foreground photo with the tracked sky photo. This would give you a sharp foreground and noise-free, incredibly detailed sky. I just bought my first star tracker and can't wait to try it out! Now I can shoot at f/2.8 and still capture plenty of light!
The Sigma 35mm Art has a lot of potential for Astrophotography, but it's up to you to make the most of it!