What do the markings "APO" and "DG" on Sigma lenses mean?

APO, with achromatic optical design, has nothing to do with low dispersion or ultra-low dispersion or fluorite lenses. It offsets chromatic aberration through the design of optical structure. It has appeared since the 18th and 19th centuries. Low dispersion lenses are only available in the 20th century. The biggest test of optical design capabilities is the pain of all optical manufacturers in Asia. Sigma is already relatively strong, but it cannot be compared with any German APO.

DG has optimized the digital camera. Compared with the previous lens, the rear lens has a better coating process to prevent light from reflecting between the low-pass filter of the digital camera and the rear lens.

DC has a smaller format and can be used normally on APS-C camera bodies. When placed on a 135 full-frame body, you will see obvious vignetting and even shadows.

EX, advanced lens, similar to Canon's "L" and red circle mark.

OS, anti-shake, similar to Canon's IS.

HSM, ultrasonic motor, similar to Canon's USM.

MACRO, macro, not micro, has a higher magnification. Although generally speaking, it can be considered macro if it is above 1:5, but macro lenses from major manufacturers can generally achieve 1:1. Or 1:3, but Sigma can't reach it.