What is coma in astrophotography?

Ever tried to shoot a picture of the night sky and ended up with stars that look just a little off?

This is going to be an incredibly quick and concise guide on coma (also known as comatic aberrations) as it pertains to astrophotography.

Let’s dive into it.

A visual representation of coma in astrophotography.
Notice the “stretched” comet-like stars.

What is coma?

Without getting to deep into the science, coma is an optical aberration that results in some points of light growing “tails”, especially near the edges of images.

This is very noticeable in some images, where stars will be perfectly circular in the center of the frame, yet appear as “comet shaped” near the corners.

Do note that, despite the very similar names, comatic aberrations are much, much different than chromatic aberrations.

How to avoid coma?

Now that you know what coma is, how do you prevent it? The most simple way to reduce coma in astrophotography is to stop down.

Oftentimes, lenses suffer the most aberrations (of any kind) when wide open, thus dropping down just a few stops (in most cases) is able to remedy the vast majority of optical imperfections.

It’s very important to note that, unlike most other types of optical flaws and aberrations, coma cannot be fixed in post-processing, thus making stopping down very important.

Man looking up at the stars.

Sony Lenses with Low Coma

The most ideal way to avoid coma in astrophotography is to just buy a lens that doesn’t suffer from it as much.

It may take a bit of digging across the internet, but many different photographers have reviewed the astrophotography performance of their wide angle lenses.

Below, I’ll include a couple of Sony E-Mount lenses that have amazing coma performance. There will be purchase links below (Amazon and B&H) along with my full reviews. Thanks for reading. 🙂

Thumbnail
Rokinon 12mm F2.0 NCS CS Ultra Wide Angle Lens for Fuji X Mount Digital Cameras (Black) (RK12M-FX) - Fixed
Sigma 14mm f/1.8 Art DG HSM Lens (for Sony E Cameras)
Title
Rokinon 12mm F2.0 (APS-C)
Sigma 14mm F1.8 Art (Full Frame)
Summary
A wide angle prime that delivers excellent sharpness and near-perfect coma control. The best astro lens for Sony a6000 series cameras.
An incredible wide angle lens that is well-loved in the astro community. Super sharp and well built, but at a high cost.
Price
Price not available
$1,209.95
Thumbnail
Rokinon 12mm F2.0 NCS CS Ultra Wide Angle Lens for Fuji X Mount Digital Cameras (Black) (RK12M-FX) - Fixed
Title
Rokinon 12mm F2.0 (APS-C)
Summary
A wide angle prime that delivers excellent sharpness and near-perfect coma control. The best astro lens for Sony a6000 series cameras.
Price
Price not available
Full Review
Buy Now
Thumbnail
Sigma 14mm f/1.8 Art DG HSM Lens (for Sony E Cameras)
Title
Sigma 14mm F1.8 Art (Full Frame)
Summary
An incredible wide angle lens that is well-loved in the astro community. Super sharp and well built, but at a high cost.
Price
$1,209.95
Full Review
Buy Now

Prefer B&H? Rokinon 12mm F2.0 (APS-C) / Sigma 14mm F1.8 Art (Full Frame)