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Hi
i have been looking at the sigma 50 - 500mm lens (no criticism on lens please) but i notice for the canon and nikon it supports hsm, where as the minolta and pentax dont, is there a difference in speed to focus or does it just mean a silent focus lens. so baisly is there a speed difference between hsm or usm or swm whatever you want to call it, and standard

Yes.

swm/usm - these lenses use a dedicated motor inside the lens that is specifically tuned to the AF characteristics of the lens. In general terms, the speed of the AF is dependent on the lens itself rather than the body to which it is attached. There can be a slight difference between bodies due to the AF module used inside the body D70 cf D2X, but it's not the deciding factor for the most part. AF operations are relatively silent due to the type of ring motor used.

non-swm/usm/hsm - traditional AF lenses. They rely on the autofocus screw drive provided by the body mount. The power of this AF screw drive varies between bodies greatly. The power of the screw drive will influence AF speed significantly - there is a big difference between say a D70 and D2x and F5. The amount of noise generated during an AF operation will depend on both the body and the design of the lens.

HSM availability for KM/Pentax - Pentax lenses as far as I'm aware all rely on body/mount screw drive AF. I'm not sure if the the appropriate contacts/info is made available in the mount contacts to drive a HSM/USM/SWM lens.

KM make a limited number of swm/usm/hsm lenses, with their system refered to SSM. The only lens I can recall without referencing their catalogue is the KM 70-200/2.8 SSM.

Chaz, one of our members is selling that very lens for a very reasonable price.....

If you're buying a Sigma lens get the HSM type if Sigma make it. It stands for 'Hypersonic Motor' and gives you focussing speed as well as low noise.

Bob.

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