PROS
- Compact.
- Weather sealed.
- 1:1 macro magnification.
- Extremely sharp from edge to edge.
CONS
- Heavy color fringing.
- Dim corners at wide apertures.
- Omits focus limiter function.
BOTTOM LINE
The Pentax D FA 100mm F2. 8 Macro WR is a very sharp compact macro lens, but it suffers from significant chromatic aberration.
Design
The D FA 100mm is very compact for a lens of its type. Its all-metal barrel, black finish, and knurled focus ring make it an equal to the HD DA Limited series in build quality, and an o-ring seal at the base completes the weather sealing. A plastic lens hood is included, but the front element is recessed, so you can probably go without a hood in most instances. Small 49mm front filters are supported.
When focused to infinity the lens measures 3.2 by 2.5 inches (HD), but the barrel extends as you focus toward the minimum focus distance, 11.8 inches. There, objects are projected onto the image sensor at life-size, a 1:1 magnification ratio.
Focus is driven by your camera’s autofocus screw. The lens can take a while to move from its closest focus distance to infinity. Unfortunately there’s no focus limiter function, so you can’t force the lens to only hunt over its close focus or distant focus range as you can with many other macro lenses.
There is a cutout on the barrel that shows a focus scale, marked in feet, meters, and magnification. It’s a useful tool for manual focus macro work, and the corresponding depth of field scale shows you just how little wiggle room you get with macro photography, even when stopped down to f/32.
Image Quality
I paired the D FA 100mm with the full-frame K-1$1,796.95 at Amazon to test the quality of the lens. At f/2.8 it scores 3,284 lines per picture height, much sharper than the 2,200 lines we want to see at a minimum from a 36MP camera. What’s more important, image quality is very even from edge to edge, with the periphery lagging behind the center by a mere 150 lines.
At f/4 the score jumps to 3,611 lines. But diffraction sets in early, with the lens dropping to 3,326 lines at f/5.6, 3,105 lines at f/8, 2,985 lines at f/11, and 2,765 lines at f/16. Those are decent results, just not as good as you get at f/4. At very narrow apertures there’s a steeper drop—2,375 lines at f/22 and 1,879 lines at f/32.
Macro photographers often stop down far in order to increase depth of field. The drop in clarity as you move beyond f/4 is moderate, but could be a concern for photographers for whom resolution is everything. It’s not uncommon for focus stacking techniques to be employed when photographing static subjects in a studio environment; you just need to shoot more images for stacking with a wider aperture.
More of a concern is chromatic aberration. Lens makers have gone a long way to reduce the strong purple color fringing you get from older lenses when used on modern digital sensors with new designs, but the optics of this lens haven’t seen changes in some time. Because of this, you’ll notice thick halos of a purple or green hue in high-contrast areas of images. This is often an issue when power lines or leaves are in a shot against a bright sky. It’s possible to remove it using Lightroom or a similar software tool, but the amount the 100mm shows is problematic at times, even at the center of the frame as you can see in the crop above.
There’s no distortion of which to speak, which is expected of a good macro lens. The corners do lag behind the center in illumination by about 1.7 stops (-1.7EV) at f/2.8. That figure is cut to -1.1EV at f/4, which is just barely noticeable in field conditions. At f/5.6 and smaller the frame is evenly lit from edge to edge.
Conclusions
There’s no questioning the resolving power of the Pentax D FA 100mm F2.8 Macro WR. At its peak it has no problem making the most of the high-resolution image sensor used by the Pentax K-1. It’s also priced reasonably, built sturdily, sealed so you can use it all types of weather, and focuses close enough to capture images at life-size. But the amount of color fringing it captures is problematic, and the long focus throw and lack of a limiter switch can certainly slow focus acquisition. There’s some room for improvement here, and we hope Pentax revisits this lens design to deliver performance similar to more modern competition like the recent Tamron 90mm Macro.
Sourse: pcmag.com
