17-70mm lens (Pentax or Tamron advice please)

Started 3 months ago | Discussions thread
Tatouzou Senior Member • Posts: 2,034
Re: Proof is in your pudding

Hythloday wrote:

Massao wrote:

For sure but some zoom lenses are better than others and Pentax DA 17-70mm is amongst the worst one in this case.

The Sigma AF 17-70mm f/2.8-4.5 DC is a very good standard zoom and a viable alternative to the Pentax offerings in this range. Generally it is capable to produce very sharp results although the corner performance leaves a bit to be desired at 17mm at large aperture settings. The vignetting level could also be a bit better here but most competitors don't offer a f/2.8 settings anyway and from f/4 it follows the mainstream. The level of distortions is about typical for a standard zoom whereas chromatic aberrations (color shadows) are comparatively low. The build quality is very fine for a lens in this price league.

Sigma AF 17-70mm f/2.8-4.5 DC (Pentax K) - Review / Test Report - Sample Images & Verdict (opticallimits.com)

The Pentax DA SMC 17-70mm f/4 AL [IF] SDM is undoubtedly the most desirable standard zoom lens in the current Pentax lens lineup. The resolution characteristic is very good without any significant weakness. The vignetting and distortion are about average for a lens in this class. The lateral CAs are relatively well-controlled although you may spot some traces in field conditions when using wide-angle settings. The quality of the bokeh (out-of-focus blur) seems to be very fine albeit limited compared to fast prime lenses naturally. Contra-light situations are handled fairly well with comparatively underdeveloped ghosting problems. Typical for most Pentax DA lenses the build quality is on a very high level. The fast and near-silent ultrasonic AF is also a very welcome new feature. All-in-all a very harmonious package selling for a very fair price of around 480€/US$.

Pentax SMC DA 17-70mm f/4 AL [IF] SDM - Review / Test Report - Sample Images & Verdict (opticallimits.com)

I agree with this review. My DA 17-70 f4 is a very good lens, which delivers sharp and very pleasing images, and has some kind of weather profing (there is a rubber gasket around the mount). Yet, there are two "caveat":

  1. it is big and heavy, which is why I often mount my DA18-135 for general photography, though the DA 17-70 is obviously better
  2. the focus ring is too loose, with a very short focus throw: if you dont care, it can easily be bumped which can lead to misfocus at the long end.

I cannot speak for the Sigma, I never handled it.

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