The Sigma 4.5mm f/2.8 EX DC circular fisheye is a photographic lens manufactured by Sigma Corporation. It is a circular fisheye lens, designed to project a 180-degree field of view in all directions onto a circular image. It is the first such lens to provide the complete circular fisheye effect on crop factor digital SLR cameras, which do not have a full 36x24mm sensor.^[1] This lens is available in Canon, Nikon, Sigma, Pentax and Sony mounts.

Sigma 4.5mm f/2.8 EX DC circular fisheye

Maker	Sigma Corporation
Technical data
Type	circular fisheye lens
Focus drive	Ultrasonic motor
Focal length	4.5mm
Crop factor	180 degrees
Aperture (max/min)	f/2.8
Close focus distance	13.5cm
Max. magnification	1:6
Diaphragm blades	6
Construction	13 elements in 9 groups
Features
Short back focus	No
Lens-based stabilization	No
Macro capable	No
Unique features	circular fisheye
Physical
Max. length	77.8mm
Diameter	76.2mm
Weight	470g (16.6oz)
Filter diameter	rear (Gelatin filter)
Accessories
Lens hood	none
Angle of view
Horizontal	180
Vertical	180
Diagonal	180
Retail info
MSRP	$1400 USD

This lens projects a 13mm image circle, which fits nicely in a Micro Four Thirds system frame with an adapter.