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Forum: Pentax SLR Lens Discussion
05-14-2017, 03:46 PM
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I do think you have better options now available that have what you are looking for- better AF, build quality, and WR. These are good reasons to make a change. The DA 18-135mm is a very good, very versatile lens that has very fast, quiet, sure AF. It is also remarkably compact for its wide zoom range. I know, it is one of my most used lenses. It can likewise hold to f/3.5-4.5 wide open from 18-70mm for good portrait results, just as shown above with the DA 17-70 f/4. I believe the DA 16-85mm will hold to f/4.5 to about 50mm. The DA 18-135mm is at its best image quality at 18-70mm, quite close to that of the DA 16-85mm. It has been downgraded mainly because of soft corner and edge performance, mainly beyond 70mm. For portrait use, and usually for longer tele FL use, the edge and corners tend to be of less importance. Central sharpness and good contrast are very good throughout its range. In another thread comparing these lenses, someone showed their DXO photo editing software able to sharpen up edges and corners of images taken at longer FL with this lens.
In my case, however, I don't have to rely exclusively on this lens. I have others, including the DA 20-40mm Limited, numerous primes including the 15mm LTD, pro-grade zooms such as a Sigma 24-60mm f/2.8, a DA* 50-135mm f/2.8, and a very wide-angle DA 12-24mm f/4 for when I really want to go for ultra quality.
If you choose the DA 16-85mm because it has better edge performance especially at the longer end, and also because you are more interested in having more wide-angle, you cannot go wrong! It still offers a wider zoom range than what you have, WR and better build quality, and better, more reliable AF.
The quality the camera body you are using also is a factor. You've not indicated which. Superior high-ISO performance, for instance will partially make up for less aperture.
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