03-14-2011, 12:51 PM
[quote name='Lampo' timestamp='1300104230' post='6742']
Thank you very much for your quick answer! Unfortunately I can not try both lenses side by side as the Sigma is officially discontinued and I have found only one shop in the Netherlands that still has the Sigma with the Pentax mount in stock. But they do not have the Pentax version of the Tamron lens, so I have to try that one somewhere else.
In my understanding both lenses are focussed by the in-camera motor of the Pentax K-5 via the slotted drive in the mount. However, there can still be a significant difference in the AF noise, as the mechanics in the lens (gears etc.) generate their own noise.
I have indeed read that the second version of the Sigma (the Macro version) has indeed good control of CA in contrast to the Tamron which has quite hefty CA at 17 mm. But what worries me is the border sharpness of the Sigma, I mean for portraits it would not matter that much, but shooting a scene indoors in low light might be a problem if I have to stop down to f5.6 to get decent borders.
[/quote]
Honestly, I do not think you have to worry about the borders, they are not very soft.
Take a look at pixel peeper, I selected any f2.8 shots from the 18-50 (the macro and non-macro version shots will be mixed as they do not have different entries for both models). Via the links you can find bigger versions of the images in flickr.
I would confidently choose the Sigma myself (I have neither, I bought the original 18-50mm f2.8 EX DC years ago and it is good enough for me, as I do not use standard zoom a lot and it actually gives surprisingly good results still).
Thank you very much for your quick answer! Unfortunately I can not try both lenses side by side as the Sigma is officially discontinued and I have found only one shop in the Netherlands that still has the Sigma with the Pentax mount in stock. But they do not have the Pentax version of the Tamron lens, so I have to try that one somewhere else.
In my understanding both lenses are focussed by the in-camera motor of the Pentax K-5 via the slotted drive in the mount. However, there can still be a significant difference in the AF noise, as the mechanics in the lens (gears etc.) generate their own noise.
I have indeed read that the second version of the Sigma (the Macro version) has indeed good control of CA in contrast to the Tamron which has quite hefty CA at 17 mm. But what worries me is the border sharpness of the Sigma, I mean for portraits it would not matter that much, but shooting a scene indoors in low light might be a problem if I have to stop down to f5.6 to get decent borders.
[/quote]
Honestly, I do not think you have to worry about the borders, they are not very soft.
Take a look at pixel peeper, I selected any f2.8 shots from the 18-50 (the macro and non-macro version shots will be mixed as they do not have different entries for both models). Via the links you can find bigger versions of the images in flickr.
I would confidently choose the Sigma myself (I have neither, I bought the original 18-50mm f2.8 EX DC years ago and it is good enough for me, as I do not use standard zoom a lot and it actually gives surprisingly good results still).