The SG-image AF 25mm f/1.8 is a compact prime lens with autofocus, developed by the Chinese manufacturer SG-image for mirrorless system cameras. Designed for APS-C format sensors, the lens was initially introduced in summer 2025 for Fujifilm X, Sony E, and Nikon Z mounts. In summer 2026, a mechanically adapted variant for the Micro Four Thirds system (MFT) followed.
Optical Construction and Image Quality
The optical design of the SG-image 25mm f/1.8 AF consists of seven lens elements arranged in five groups. To reduce chromatic aberrations and improve edge sharpness, this design uses three lenses with particularly high refractive index.
The aperture construction consists of nine circular blades, which allows a uniform, circular opening even when stopped down and is intended to support soft background blur.
The adjustable aperture range goes from f/1.8 to f/16. The minimum focusing distance is 0.3 meters, making the lens suitable for close-up shots.
The focal length of 25 millimeters corresponds to a field of view of approximately 37.5 millimeters in full-frame format when used on an APS-C camera, and a normal focal length of 50 millimeters on an MFT sensor.
Build and Housing Design
The outer housing of the lens and the bayonet mount are entirely made of metal, giving the construction high robustness. With a weight of approximately 145 grams and a length of only 32 millimeters, the housing is lightweight and compact.
The filter thread on the front has a diameter of 52 millimeters. The lens is available in various color variants, including classic colors black and silver as well as limited editions in red and orange.
Autofocus System and Electronics
For focusing, the lens uses an integrated STM stepping motor. This operates largely silently in everyday photography and supports modern camera functions such as eye autofocus from camera manufacturers. Since focusing is internal, the filter thread does not rotate during focusing.
Electronic contacts on the mount transmit all relevant EXIF data to the camera. On the lens mount housing, there is also a USB-C interface that allows end users to directly install firmware updates to optimize autofocus compatibility.
Sample Images
Some sample images taken with the lens and the Fujifilm X-T20. You can find a detailed review of the lens here.
