Rokinon 18mm f/2.8 & Samyang 14mm f/2.8

Why these two together

Both of these lenses exist to answer the same question: how much sky can I cover, how fast, for how little. A meteor lands somewhere random and lasts a fraction of a second, so the two variables that decide whether you catch it are the amount of sky in frame and the aperture. Neither is negotiable, and neither of these lenses asks you to pay much for them.

They differ mainly in how far they push it. The 14mm covers about 115 degrees diagonally on full frame — close to the practical limit before the sky starts looking distorted. The 18mm covers around 100 degrees, which is still very wide but noticeably easier to compose with, and it is tiny and light in a way the 14mm is not.

The Samyang 14mm f/2.8

This is the older design and the one with the reputation. It is fully manual, it is heavy, and it has a bulbous front element with a fixed petal hood, which means no screw-in filters at the front at all. What it gives you in return is an enormous field for very little money.

It is not a clinically perfect lens. There is coma in the corners wide open — bright stars grow small wings — and there is a distinctive moustache distortion that matters if you photograph architecture and does not matter at all if you photograph sky. Stopping to f/4 tidies the corners considerably, though at f/4 you have given up much of the reason you bought it. My approach is to shoot it at f/2.8 and accept the corners, because for a meteor frame the corners are not the subject.

The Rokinon 18mm f/2.8

Much newer, much smaller, and it autofocuses — worth saying, because Samyang's manual reputation is strong enough that people assume otherwise. It weighs almost nothing, takes ordinary 58mm screw-in filters, and lives in a jacket pocket. Corner performance wide open is better than the 14mm's, and the modest reduction in coverage is a fair trade for that.

For a night on the lawn with strangers, this is the one I would hand to somebody else. It focuses itself if it has to, it is small enough not to unbalance a light tripod, and it is hard to get a bad frame out of it.

Which to use for what

Getting the best out of either

• Focus by hand regardless. Even on the autofocus 18mm, switch to manual at night, magnify live view on a bright star and set it yourself. Autofocus hunts on stars and the infinity mark on a manual lens is not trustworthy — most of them focus past infinity by design, to allow for temperature.
• Tape the ring. A strip of gaffer tape over the focus ring after you set it saves the night you would otherwise lose to a knock in the dark.
• Shoot wide open. These lenses are bought for f/2.8. Corner coma is a smaller problem than a meteor too faint to record.
• Watch the corners for gradients. Ultra-wides see a lot of horizon, and at 115 degrees you will have streetlight in the frame whether you meant to or not. Compose so the worst of it falls where the foreground is.

Buying

Samyang and Rokinon are the same lenses under different names, which means the used market is bigger than it first appears — search both. The manual 14mm has no electronics and no moving motor, so a clean used copy is a safe purchase; check the front element carefully, since the protruding design and fixed hood make it more exposed to knocks than a conventional lens. The autofocus 18mm does have a motor, so confirm it drives smoothly and quietly before buying used.

Both live on the A7 III, and the settings I use with them are written up in the camera Milky Way guide.