Astrophotography is a fascinating and often rewarding field of photography. Capturing the wonder of the Milky Way is incredibly satisfying, but it requires a lot of practice and technical knowledge. Most beginners assume that, if they have a good camera, astrophotography should be easy. In reality, the lens you use is just as important as the body. The technical quality of your photos is affected mostly by the lens you choose. In this article, we’ll look at how to select the right glass for the occasion.

Aperture and Focal Length

Two of the most important features for an astrophotography lens are aperture and focal length. They will determine how your pictures turn out.

Aperture is a measure of how wide open the lens is. It’s measured in f/ stops, with lower numbers representing wider apertures. Focal length refers to the optical distance from the lens to the image sensor. It’s measured in millimetres (mm) and relates to how much of a scene is captured. The lower the number is, the wider the field of view.

For Milky Way photography, you should opt for a lens with an effective focal length of less than 35mm. For an APS-C camera, this means you’ll need a lens with 24mm focal length, and with a micro 4/3 sensor, a 16mm.  The advantage of the shorter focal length is that it gives you a broader field of view, meaning you can capture more of the night sky. It also means you can have a longer shutter speed.

For night photography, you’ll need to choose a wider aperture. Ideally, this will be under f/2.8. This allows sufficient light to enter the sensor.

Aberrations

The term ‘aberrations’ refers to imperfections in the way a lens captures light. In astrophotography, there are a few different aberrations that can affect you:

Chromatic Aberration

This term is also known as colour fringing. It causes blurry edges in high-contrast situations. Stars, for example, can often have a purple halo in images with a lot of chromatic aberration. Although it’s possible to correct such imperfections, is best not to have them in the first place.

Spherical Aberration

This phenomenon makes stars appear with a halo around them. They’re not as common as other aberrations, and it’s not too detrimental. However, stopping down your aperture can solve the problem.

Comatic Aberration

Another common aberration is comatic or coma. This effect often occurs at the edges of the frame and gives stars a comet-like tail. Again, stopping down the aperture of your lens can resolve the issue.

Astigmatism

Astigmatism is often confused with coma, as the effect can appear the same. Light is spread, making stars look like lines. It’s a common effect even with expensive lenses.

Recommended Lens

You may already have a lens that’s suitable for night sky photography. It’s a good idea to take some test shots to find out whether or not what you have can capture the Milky Way. If not, here are some lenses that deliver good astrophotography results:

• Rokinon Wide Angle. These budget lenses come in a range of sizes and are excellent at controlling aberrations.
• Sigma Art Wide Angle. A slight step up from the Rokinon is the Sigma range. They offer excellent sharpness and almost no aberration. However, they are expensive.
• Tamron 15mm – This lens also provides exceptional sharpness and aberration control, as well as a useful zoom range.