Abbreviation: HSM = "Hyper-Sonic Motor" (Sigma)
The abbreviation HSM means "Hyper-Sonic Motor" and is seen on Sigma products.
Explanation from Sigma
This lens uses a motor driven by ultrasonic waves to provide a quiet, highspeed AF.
See examples of effected products
 | Sigma EX 70-200mm F2.8 APO HSM DG OS |
 | Sigma 50-200mm F4-5.6 DC OS HSM |
 | Sigma EX 120-300mm F2.8 APO DG HSM |
See links
| sigmaphoto.com |