Originally posted by DSims Do you have more evidence on this (either qualitative or quantitative)?
This doesn't mesh with my experience, or with some comments I've read from others (e.g. F*300 or FA*300/4.5 focus faster than DA*300).
Of course, the specific camera model's important when comparing screw-drive on Pentax, with the latest models being better.
Well I own Sigma EX 70-200 ,Sigma EX DG 50 macro , da40 , Sigma 400 Telemacro , Sigma Bigma and multitude of cheap screw lens (28-80, 18-250, 70-300 etc etc)
In Sdm/HSM
I own da*16-50, da* 50-135 , da* 55 , da* 300 , Sigma ex DG OS HSM 70-200.
Models I have extensive experience of
k10d ,k20d,Kx, k5 and k3
I shoot an average 500+ sport images a week in low light varying from linear tracking to spot tracking.
I also have quite a lot of exposure to Canon / Nikon FF bodies with lens like Canon 200mm EF f2L
Don;t mistake focus 'speed' with tracking ability
High screw drive focus speed means low torque which in turn mean changing direction takes time....ie poor tracking ability
HSM (ring type) is moderately slow but because its direct drive and short throw makes it ideal for tracking.
The da* 300 suffers from too weak a motor needing ling throw and as such is a halfway house in performance.
as I said "all but the most 'sport' tuned glass are better."
So don't see that in conflict with "with some comments I've read from others (e.g. F*300 or FA*300/4.5 focus faster than DA*300)."
I don't know the fa300 but my Sigma 400 being short throw and rear focusing is fast (rear focus low weight and lower latency )
There is a reason screw is nothing but a legacy option dropped by most manufacturers , They didn't drop it because its better !
Last edited by awaldram; 02-05-2014 at 07:05 AM.