Originally posted by cajuncutter So how dependable are these af motors and how fast are they?
The AF motors in Sigma lenses have probably undergone some evolution. I think your model - the APO DG AF - was the first non-screw drive 70-200 they made, but I'm not sure it includes what they later called their 'HSM' autofocus motors.
Over time they have tweaked and improved the performance of the 'HSM' AF motors within the lenses that feature it. All I can say is that the AF in the Sigma 70-200 HSM II I own is very fast.
For info, from what I can tell, looking around PentaxForums, DPR and other sites, the Sigma 70-200mm F2.8 design history seems to be:
- 70-200mm F2.8 EX APO DG- Original version, minimum focus distance 1.8m, screw drive, screw drive then then HSM (?) (1998/9)
- 70-200mm F2.8 EX APO DG - HSM, no screw drive, 'digitally optimized' lens coatings to reduce flare, MFD 1.8m (2005)
- 70-200mm F2.8 EX DG Macro (HSM) - HSM, macro feature, minimum focus distance reduced to 1m (2006)
- 70-200mm F2.8 EX DG Macro HSM II - Improved optical performance (2007)
- 70-200mm F2.8 EX DG OS HSM - All-new design with built-in Optical Stabilization (2010)
- 70-200mm F2.8 DG OS HSM | Sport - New optical design (2018)
Lenstip also have a handy table showing the differences between last five Sigma 70-200 f2.8s (as of 2018):
https://www.lenstip.com/porownaj.php?co=obiektyw&ile=5&add0=1572&add1=911&ad...d3=42&add4=511