SG-image AF 55mm F1.8

The SG-image AF 55mm F1.8 is an autofocus standard prime for full frame mirrorless cameras. SG-image lists it for Sony E, Fujifilm X and Nikon Z. The 55mm focal length is a classic normal view with a 42 degree angle of view, and the manufacturer pitches it as a go-to walkaround lens for portraits, street scenes and everyday use. On the Fujifilm X mount, which has a smaller sensor, the lens works as a short telephoto.

Optical design

According to SG-image the lens has 10 elements in 8 groups. The diaphragm has 9 blades and runs from F1.8 to F16 with an automatic aperture, so there is no aperture ring. The minimum focus distance is 0.5 m with a maximum magnification of 1:9.1. SG-image says the design is optimized to keep distortion, chromatic aberration and vignetting low and to deliver sharp images across the frame even wide open. These are claims by the manufacturer. No special glass types are named.

Autofocus and handling

SG-image describes the autofocus as fast, precise and quiet, suited to street, event and portrait work including eye tracking. A retail listing mentions a stepping motor (STM) and full-time manual focus override. The aperture is controlled from the camera, as the spec sheet lists an automatic aperture.

Build and size

The barrel is metal. The lens measures 69 mm in diameter and 78 mm in length, weighs about 365 g and has a 58 mm filter thread. That puts it in the usual range for an F1.8 normal prime, heavier than the pancake-style lenses SG-image sells but still compact for full frame.

Where it fits

Typical alternatives in the database are the Sony FE 50mm F1.8 for Sony E and the Nikon Nikkor Z 50mm F1.8 S for Nikon Z, both from the camera makers, while the 7Artisans AF 50mm F1.8 covers Sony E and Nikon Z at the budget end. SG-image positions its lens at a much lower price than professional zooms, though prices can change. For the Fujifilm X mount, options within the database include the 7artisans 55mm F1.4 (manual).

Pros and cons

Pros

• Autofocus on a full frame normal prime
• Bright F1.8 aperture with 9 blades
• Metal barrel
• Common 58 mm filter size
• Offered for three mounts, including Fujifilm X

Cons

• No aperture ring
• No stabilization
• At 365 g and 78 mm it is larger than SG-image's pancake lenses
• No weather sealing mentioned
• Limited independent test data

Verdict

The SG-image AF 55mm F1.8 is a straightforward budget autofocus normal prime for full frame Sony E and Nikon Z, with a Fujifilm X option. It makes sense for buyers who want a fast autofocus lens at the lowest cost and can live without weather sealing, an aperture ring or published test data.