Each lens are made in accordance with the features and functions that it has. And the following are codes on Sigma lenses and the meaning to each one.
EX – EX Lenses are premium lenses in the Sigma lens product line, like the L Series of Canon lenses. It’s no surprise that EX coded lenses are usually relatively expensive.
DC – DC Lenses are lenses designed specifically for cameras with a
DG – DG lenses are Sigma lenses designed for both the full-frame and cropped sensors.
OS – OS is short for Optical Stabilizer (equivalent to the IS or VR). It functions to lessen tremors when photographing in low shutter speeds or when photographing with a telephoto lens.
HSM – Hyper Sonic Motor uses a quieter motor technology (silent focusing) and has a better focusing speed.
ELD – Extra Low Dispersion. Lenses with this code uses special optics that minimizes chromatic aberration, flare, and ghosting.
SLD – Special Low Dispersion. It’s almost the same as ELD but of a higher class/quality, making it more expensive.
FLD – Fluorite Low Dispersion. These uses a low-dispersion element that containing fluorite.
APO – Apochromatic lenses. APO lenses are designed to minimize chromatic aberration (purple fringing).
ASP – Aspherical lenses; it has a complex element design to fix photo quality in general and lessens the size and weight of the lens.
IF – Inner focusing lenses focuses by moving internal elements rather than frontal elements. This means that when this lens focuses, the frontal elements doesn’t rotate along (very useful when using a CPL Filter). Also, IF lens bodies do not change (doesn’t get elongated or shortened) when focusing.
RF – Rear Focusing lenses focus by moving the rear elements.
CNV – These lenses can be coupled with a teleconverter.