Andy Westlake tests Sigma’s unconventional SA-mount mirrorless camera, the sd Quattro
Sigma sd Quattro review: Autofocus
One disadvantage of using DSLR lenses on a mirrorless camera is that they’re often slow to focus, as their autofocus motors and optical designs are optimised for phase- detection autofocus. Sadly, Sigma hasn’t found any magic solution to this, and with the 30mm f/1.4 DC HSM | Art lens I used for testing, the AF speed could best be described as ‘leisurely’. I found it adequate for static subjects, but wouldn’t even think of trying it with anything that moves. Of course, it’s possible that the camera might function better with other lenses.
Many users, however, will be tempted to focus manually, and here the sd Quattro offers some useful aids. A peaking display can be turned on in the menus with a choice of four colours, although it can’t be set up as a custom viewfinder display. When the lens is switched to manual focus, pressing the button in the centre of the D-pad engages magnified live view for the most accurate focusing, and the area of interest can be moved around the frame as in AF mode.
The sd Quattro isn’t the best choice for anything that requires quick focusing, such as street photography. But its limitations will be of less concern with the subjects that the Foveon sensor best lends itself to, such as macro, still life or landscapes.