Buyers must first distinguish between FX (Full Frame) and DX (APS-C) formats to ensure sensor compatibility. Key technical factors include the Mount Type (traditional F-Mount for DSLRs vs. the newer Z-Mount for mirrorless systems), Aperture Range (e.g., f/2.8 for low-light performance), and Optical Construction (number of elements/groups). High-quality lenses should feature ED (Extra-low Dispersion) glass to minimize chromatic aberration and Nano Crystal Coat or ARNEO coating to reduce ghosting and flare.