Player One 2.5mm CS-Mount All-Sky Lens

Product Overview

The Player One 2.5mm CS-Mount All-Sky Lens is a very short focal-length lens that turns a small-format planetary or guide camera into an all-sky monitor. At 2.5 mm it delivers a 170° field of view on a 1/2″ sensor — wide enough to take in nearly the entire sky in a single frame. It threads on via the standard CS mount and is metal-bodied. Player One optimizes it for their 1/2″-format cameras, the Neptune series in particular.

Who It's For

This is a good match if you run a 1/2″-format planetary or guide camera (such as a Neptune-M, Neptune-C, or Neptune-C II) and want to point it at the whole sky for cloud, meteor, or aurora monitoring. It also works as a very wide finder-style lens on a guide camera.

Key Features & Design

• 2.5 mm focal length: an ultra-short focal length that yields a 170° field on a 1/2″ sensor.
• CS mount: threads onto any CS-mount camera, including Player One planetary and guide cameras.
• Matched to 1/2″ sensors: the 170° coverage is stated for the 1/2″ format — the Neptune series in particular.
• Metal construction: a compact, durable barrel.

Optical Design

The all-sky field comes directly from the focal length and sensor size: a 2.5 mm focal length projected onto a 1/2″ sensor spans roughly 170°, which is why such a short lens captures the whole dome of the sky rather than a narrow patch. The CS mount is the standard machine-vision lens interface (a C mount shortened by 5 mm of flange distance) used by compact astronomy cameras, so the lens seats at the correct back-focus without an adapter on a CS-mount body.

Recommended Uses

All-sky monitoring — clouds, meteors, satellites, aurora — with a 1/2″ planetary camera, and use as a wide-field lens on a guide camera.

Compatibility and Accessory Notes

The lens uses a CS mount and is matched to 1/2″-format sensors such as the Neptune series. On a larger sensor the 170° figure no longer applies and the image circle may not fill the frame. If you are pairing it with a different camera and are unsure of the fit, send us your camera model and we will confirm it with you.

Good to Know Before You Order

• 1/2″ format: the 170° field is specified for a 1/2″ sensor (Neptune series); a larger sensor changes the coverage.
• CS mount: it needs a CS-mount camera; a C-mount body requires a 5 mm CS-to-C spacer, sold separately.
• Lens only: the camera and any mounting are not included.

Frequently Asked Questions

Is it difficult to set up?

No — thread it onto a CS-mount camera and adjust focus at the lens. Nothing else is required.

What camera is it for?

A 1/2″-format planetary or guide camera, such as the Player One Neptune-M, Neptune-C, or Neptune-C II.

What field of view does it give?

170° on a 1/2″ sensor — an all-sky view.

How is it different from the 2.1mm lens?

The 2.1mm lens is matched to the smaller 1/3″ format (Mars series) and gives a 150° field; this 2.5mm lens is matched to the 1/2″ format and gives 170°.

Bottom Line

In short: a 2.5 mm CS-mount lens that gives a 170° all-sky field on a 1/2″ sensor, matched to the Player One Neptune series for whole-sky monitoring.