Advice please. 70-200 lens

[Blueheeler]

Folks,

I'm considering upgrading my long lens to a new 70-200 on my Pentax K5. My two best options at the moment are the Sigma 2.8 APO EX DG OS HS and the Tamron SP AF f/2.8 Di LD (IF) Macro. These match my criteria of being long enough and fast enough for portrait work to action shots. I already have the 10-70 range covered with a couple other pieces of glass and can't really see a need to go longer than 200. The K5 has an APS-C chip anyway so it's an effective range of 320 or thereabouts.

Does anyone have any experience of either or both of these?

Also, I note the Sigma has inbuilt image stabilisation which the Tamron does not. My K5 already has on board shake reduction (which gives me satisfactory results) and I understand that one does not use both body and lens stabilisation simultaneously.

Any thoughts on the Sigma OS stabilisation being superior/inferior to the K5 on board stabilisation?

Any other comparative thoughts between the two?

The Sigma is about AUD$450 more than the Tamron so is it $450 optically better, or is that just the price of in-lens stabilisation.

Any comments appreciated.

Thanks

Ray

[Donald]

I don't know either lens. But I think we can say that a significant part of that greater cost will be for the stabilisation. I know you meant something in addition to OS when you then asked about being 'optically better', but hold on to the fact that the OS in itself, in my view, more than compensates to a huge degree for any difference that may exist.

However, the reality is that any differences will really only come into play if you're going to be printing at fairly large sizes. For web publication and small scale printing, you'd be hard-pushed to detect differences.

Far more important, in my view, is being able to have OS.

[Manfred M]

According to DPreview the Sigma is not as good optically as the Tamron, but the Tamron autofocus system is not all that fast or accurate and is noisy. Both lenses sound like they have significant flaws.

http://www.dpreview.com/lensreviews/...-200_2p8_c16/6

http://www.dpreview.com/lensreviews/...70-200_2p8_n15

[GrahamS]

Ray - I got much better image stabilization results with my K7 (same as K5) when using long lenses with stabilization built-in the lens. The camera stabilization system (SR) works great with lenses up to around 150mm but at 200mm and more it's not as good as the Sigma OS system.