Pentax DA 17-70 f4

Pentax’s SMCP-DA 17-70 f4 AL (IF) SDM lens is the second tier standard zoom in Pentax’s DA lineup, right behind the DA* 16-50 f2.8. As such, it’s the best choice for those who don’t want the much pricier and heavier DA* 16-50. Because the lens has been plagued by reports of auto-focus issues, used prices are now slipping below $300, which is about half what the lens goes for brand new. With Pentax announcing a new standard zoom (namely, the HD DA 16-85 f3.5-5.6), there is a real question whether the DA 17-70 will remain in production (for if sales of the lens fall, Pentax may decide to withdraw the lens from production). This could lead to even more used DA 17-70s hitting the used market, driving prices down even further. Auto-focus issues aside, how good is the DA 17-70 optically? What kind of images can you draw from it?

Except for the long end of the lens (around the 65 to 70mm range) the lens is fairly sharp, although it is not quite prime lens sharp. It is still, however, decently sharp, capable of producing more than enough resolution for most uses. Where the lens really excels over some of Pentax’s consumer grade standard zooms such as the (DA 18-55 and even the DA 18-135) is in attainable lens contrast and color rendition.

Let’s examine some crops. All the following images were imported into Lightroom and post-processed. The default Lightroom settings for sharpening were used. We’ll begin with the following photograph, shot at 17mm, f8:



Now let’s look at the 100% crop:



And the 100% edge crop:



That’s fairly respectable performance for zoom lens with this range. The center is sharper than the edges, but keep in mind, in this image the edges are further from the camera than the center. Let’s examine another 17mm, f11 image:



The 100% center crop:



The 100% corner crop:



Again, respectable performance. Honestly, there’s isn’t much to complain about here. If you need more resolution out of a zoom lens with comparable range, buy a Canon full frame camera and the Canon 24-105 f4 L lens.

Let’s try an image taken at 19mm, f8:



Please note: the image above is corrected for perspective distortion. The following crops are not. First, the 100% center crop:



The 100% corner crop:



Let’s try an image taken at 25mm, f8:



The 100% center crop:



And the 100% corner crop:



It could be argued that the DA 17-70 is a little sharper around 25mm than it is at the wide end of the lens. However, the differences are subtle and not important enough to dwell on.

Now for an image taken at 28mm, f8:



The 100% center crop:



And the 100% corner crop:



Again, very good edge to edge performance. Nothing really to complain about at all.

Let’s try an image at 39mm, f8:



The 100% center crop:



And the 100% corner crop:




In this image, we clearly see a branch in the far corner that’s not in focus. But the branch is closer to the camera and thus falls out of the plane of focus. The rest of the detail appears well captured, edge to edge.

Here’s an image shot at 53mm, f8:



The 100% center bottom crop:



The 100% corner crop:



Performance remains pretty good, even at 53mm. Let’s see what’s going on at 58mm, f8:




The 100% center crop:



The 100% corner crop:




Here we might be seeing slight reduction in resolution, particularly when compared to how the lens performs in the middle of the zoom.

Here’s a shot taken at 63mm, f8:



And the 100% center crop:



Really quite decent performance here. I won’t bother posting a corner crop on this image, since there’s no detail in the plane of focus with this image toward the edges.


And now, a center crop of an image taken at 70mm, f8:



And the 100% corner crop:



Here we definitely see a reduction in resolution. Images soften up quite a bit at the long end of the zoom. Here’s another 70mm, f8 sample:



And the 100% center crop:



And the 100% corner crop:



Pretty much the same as before. Somewhere in the 60mm range, the DA 17-70 starts losing resolution, so that by the time you reach 70mm, don’t expect to get images that rival the sharpness found at other focal lengths.

What about wide open performance? Let’s glance at an image taken wide open at 23mm:



And the 100% center crop:



And the 100% corner crop:



Very respectable performance at f4. Sharp in the center, less sharp in the corners; but you would expect that in a 17 to 70 zooms lens. As with most mid-level and prosumer zooms, if you want better performance in the corners, stop the lens down.

Given the range, the DA 17-70 performs quite well. Although it’s not quite perfect, it’s still very good throughout most of its range, maintaining very good edge to edge resolution from 17mm to around 60 to 65mm. It also focuses fairly close (.31x magnification), is well constructed, features very good contrast and color rendition, and works very well as a landscape lens. CA control, while not perfect, is actually quite good for a zoom lens. There is some distortion on the wide end, as is to be expected with a zoom lens with this sort of range; but it’s not horrible. Optically, it’s a dependable, versatile, workhorse lens.

If there is a flaw in the lens, it is the SDM motor, which is slow and has developed a reputation for poor durability. Now I have no idea to what degree this bad reputation is deserved. I can’t say, in terms of percentages, how many people have actually had problems with the motor burning out. It could be 5%, 10%, 15%, or even higher. It’s difficult to make an estimate without hard data. But there’s enough complaints online that it’s definitely something to take into consideration when evaluating the lens.

Yet that is not the only issue with the lens’ AF performance. There are also reports that the DA 17-70 doesn’t focus accurately, particularly on the long end. Again, I’m not sure how widespread this is. I experienced an issue with the first copy of the lens I received from keh.com. That lens had some sort of defect in the firmware that prevented it from accurately reporting to the camera the correct focal length. Regardless of the real focal length, whether it was 17mm, 24mm, 50mm, or 70mm, the lens reported only 43mm. Without the correct focal length, the lens could not focus accurately at the wide or long ends of its zoom range. I returned the product to keh.com and received a second copy, which I have shot on the K-5iis and K-5 without any serious issues relating to the AF. AF can still struggle in low light and at far distances; but beyond that it has been reasonably okay, although hardly stellar. Otherwise, performance is on par with many other standard zoom lenses I’ve used. Both of the copies of the DA 17-70 that I received from keh.com were optically very good, with very similar rendering and resolution performance between the two lenses.

One issue to be aware of with this lens involves what could be called “veiling flare,” or loss of contrast in strong, bright light. This is a lens with a lot of glass in it, and so it would be unrealistic to expect the optic to resist flare as well as a prime lens or a zoom with less glass or a lens using nano coating technology. Also, the lens does not transmit as much of the blue color spectrum as limited primes and zoom lenses with less glass like the DA 12-24 and the DA 10-17. Although the blue color rendering of the lens is really quite good (easily better than the DA 18-55 and even better than the DA 16-45), I don’t think it matches either my DA 15 or the DA 10-17 and DA 12-24 (nor any of the DA star or other limited lenses). Again, I’m not suggesting this lens can’t produce excellent results when it comes to blue tones; only that those other lenses are at least slightly superior. The DA 15, for example, will, in my experience, accentuate the blue in reflections off water to an extent that the DA 17-70 can’t quite match.

More sample images from the DA 17-70, first from the AF challenged version:













And from the second version.

At 17mm:



At 21mm:





At 25mm:



At 30mm:



At 36mm:



At 53mm:



At 70mm:







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