In summary
The HD PENTAX-D FA 28-105mm f/3.5-5.6 ED DC WR lens is compact, light weight, affordably priced, well built, and offers decent weather-resistance. The AF system is a bit behind the times when compared with some of the newer lenses we’ve tested, and its Imatest performance is also not quite as good as we’ve obtained with those lenses.
Full review
Released in early 2016, the HD PENTAX-D FA 28-105mm f/3.5-5.6 ED DC WR is a compact and lightweight standard-range zoom lens that was designed primarily for the company’s DSLR cameras. On its cropped-sensor K-3 series, such as the K-3 Mark III used for this review, the range is equivalent to 42-157.5mm, which is also convenient for many potential users. This lens features the Pentax Quick-Shift Focus System, which allows delay-free switching from autofocus to manual-focus when the subject is focused by the camera’s AF system.
Side view of the HD PENTAX-D FA 28-105mm f/3.5-5.6 ED DC WR lens. (Source: Ricoh Imaging.)
The optical design (shown below) contains 15 elements in 11 groups and includes two high-precision aspherical optical elements, one ED (Extra-low Dispersion) glass optical element and one anomalous-dispersion glass optical element to deliver sharp images with minimal chromatic and spherical aberrations. A high-grade, multi-layer HD (high-definition) coating ensures greater light transmittance and less reflection to minimise ghosting and flare.
This diagram shows the positions of the exotic glass elements in the HD PENTAX-D FA 28-105mm f/3.5-5.6 ED DC WR lens. (Source: Ricoh Imaging.)
Eight weather-resistant seals keep out moisture and dust, while the front element is treated with a Super Protect coating that can also provide protection against accidental impact. The nine-bladed iris diaphragm contributes to a pleasing bokeh quality across the aperture and focal length range and becomes completely circular between f/3.5-6.3 at the 28mm focal lengths and between f/5.6-10 at 105mm.
This diagram shows the eight weather-resistant seals in the lens barrel. (Source: Ricoh Imaging.)
Autofocusing is driven by a Supersonic Direct-Drive Motor (SDM), which is fast, quiet and smooth in operation. This lens is compatible with both the full-frame K-mount Pentax DSLRs as well as APS-C models like the K3 series, where it covers a 43-161mm equivalent focal length range.
It is supplied with front and end caps plus the PH-RBS62 petal-shaped lens hood. An optional S-80-120 Soft Lens Case is available to protect lens during transport or storage.
Who’s it For?
This lens will only be relevant to users of Pentax DSLR cameras, for whom it provides a general-purpose, standard zoom lens. Its 28-105mm zoom range is better suited to general use than the 43-161mm range on the cropped-sensor cameras, although its light weight and compact size make it a reasonably good match for those cameras.
Build and Ergonomics
With a base weight of 440 grams (463 grams with the supplied hood) this lens is relatively light without being flimsy. It’s a good match for the K-3 III body we used for our tests.
Ricoh doesn’t specify the materials this lens is made from but the metal mount5ing plate is solid and snug-fitting. There are two inner barrels that extend as you zoom from the 28mm to the 105mm position, which adds about 55 mm to the overall length of the lens. We found no slackness in the lens when the barrels were fully extended.
The zoom ring is located near the front of the outer barrel, just behind a 5 mm wide branding ring, which carries the name of the lens. Around its leading edge is a thin ring of anodised green.
The entire zoom ring is just under 55 mm wide, with most of its surface covered in a textured rubber-like cladding that provides a non-slip grip. A 7 mm wide strip around its trailing edge carries focal length marks for the 28mm, 35mm, 50mm, 70mm, 90mm and 105mm positions, which line up against a white line on the fixed, 11 mm wide section of the lens barrel behind the focusing ring.
Just behind the trailing edge of the zoom ring is a 9 mm wide focusing ring, which is entirely covered in the same rubber-like cladding as the zoom ring. Since focusing is driven from the camera, this ring turns through 360 degrees when power is off but operates smoothly and positively when in actual use.
Stamped on the top of the fixed section of the lens barrel are figures denoting the aperture and focal length limits of the lens: 3.5-5.6 / 28-105. Around the left hand side is the DFA branding stamp, while the PENTAX brand is located on the opposite side of the lens barrel.
Above each of these stamps, the lens barrel carries a 20 mm long strip of fine, low-profile ridging to provide a grip for when the lens is fitted or removed from the camera. It’s a very nice touch.
The solid metal lens mount is surrounded by a red rubber ring that keeps out moisture and dust. Just inside this o-ring are seven contact points for transmitting data between the camera and the lens. Unusually, the reference mark for mounting the lens is a red dot on the outer edge of the lens mount. It works well but, like many other features of Pentax gear, it’s not in th4e same place as similar features on other manufacturers’ lenses (or cameras).
Performance
Our Imatest tests showed the review lens just able to meet expectations for the K-3 III’s 26-megapixel sensor in the centre of the frame at shorter focal lengths and with wider aperture settings. It fell short with measurements taken roughly half way out from the centre but those taken near the periphery of the frame were only a little less, indicating decent average performance.
Diffraction kicked in pretty solidly at around f/11 and resolution plunged dramatically, especially for the off-centre measurements. The graph below shows the results of our tests.
Lateral chromatic aberration remained mostly in the ‘negligible’ range, as shown in the graph below, with the lowest figures being for the shorter focal lengths. We found no evidence of coloured fringing in test shots.
With all internal lens corrections switched off we found vignetting was very low and not evident at any of the focal length settings. Rectilinear distortion was also low, ranging from slight barrel distortion at 28mm through to visible pincushion distortion at 105mm. Since both aberrations are addressed with in-camera corrections neither would be an issue.
Autofocusing was a mixed bag and hunting occurred frequently in the AF-S mode when focusing on close subjects and with low-contrast scenes. The lens often lost focus in the AF-C mode while following moving subjects when shooting video.
Backlit subjects were mostly handled well, partly because the K-3 III can record a relatively wide dynamic range. However, bright areas in backgrounds caused frequent problems with the AF system, leading to a second or two of hunting.
As usual, bokeh in close-ups at wide aperture settings depended a lot on background lighting. We found some odd-looking donut-shaped highlights in some shots, while highlight outlining was relatively common.
The 50 cm close-focusing limit of this lens restricts its use to larger subjects, even at the 105mm focal length, where the maximum magnification is roughly one fifth life size.
Conclusion
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SPECS
Picture angle: 15.5 to 53 degrees (23.5 to 75 degrees as reviewed on Pentax K3 III camera)
Minimum aperture: f/22 to f/32
Lens construction: 15 elements in 11 groups (including 2 aspherical, 1 ED and 1 anomalous-dispersion glass elements); multi-layer HD (High Definition) and SP (Super Protect) coatings
Lens mounts: Pentax KAF3
Diaphragm Blades: 9 (circular aperture)
Weather resistance: Yes
Focus drive: SDM (Supersonic Direct-Drive Motor) DC motor with Quick-Shift control
Stabilisation: No, relies on IBIS in camera
Minimum focus: 50 cm
Maximum magnification: 0.22x
Filter size: 62 mm
Dimensions (Diameter x L): 73 x 86.5 mm
Weight: 463 grams with hood
Standard Accessories: Front and end caps plus PH-RBC62 lens hood
Distributor: C.R. Kennedy & Company, (03) 9823 1555
TESTS
Based upon JPEG files taken with the Pentax K-3 III camera.
SAMPLES
Vignetting at 28mm f/3.5.
Vignetting at 35mm f/4.0.
Vignetting at 50mm f/4.5.
Vignetting at 70mm f/4.5.
Vignetting at 90mm f/5.6.
Vignetting at 105mm f/5.6.
Rectilinear distortion at 28mm.
Rectilinear distortion at 35mm.
Rectilinear distortion at 50mm.
Rectilinear distortion at 70mm.
Rectilinear distortion at 90mm.
Rectilinear distortion at 105mm.
28mm focal length, ISO 200, 1/20 second at f/11.
105mm focal length, ISO 200, 1/20 second at f/10.
Close-up at 28mm focal length, ISO 100, 1/60 second at f/3.5.
Close-up at 150mm, ISO 100, 1/25 second at f/5.6.
Close-up at 105mm, ISO 400 1/3200 second at f/5.6.
Backlit close-up at 105mm, ISO 100, 1/800 second at f/5.6.
Crop from the above image magnified to 100% to show the donut-shaped highlights in out-of-focus areas.
Backlit close-up at 70mm, ISO 100, 1/1250 second at f/5.6.
Backlit close-up at 28mm, ISO 100, 1/500 second at f/5.6.
Sunstar plus flare artefacts at 28mm, ISO 100, 1/8 second at f/22.
Sunstar at 28mm focal length, ISO 100, 1/200 second at f/22.
52mm focal length, ISO 100, 1/500 second at f/6.3.
28mm focal length, ISO 100, 1/125 second at f/8.
58mm focal length, ISO 100, 1/100 second at f/4.5.
68mm focal length, ISO 100, f/60 second at f/4.5.
62mm focal length, ISO 200, 1/5 second at f/22.
105mm focal length, ISO 200, 1/100 second at f/5.6.
28mm focal length, ISO 200, 1/60 second at f/3.5.
95mm focal length, ISO 1600, 1/30 second at f/5.6.
Additional image samples can be found with our review of the Pentax K-3 III camera.
Rating
RRP: AU$865; US$499.99
- Build: 9.0
- Handling: 8.8
- Image quality: 8.7
- Autofocusing: 8.5
- Versatility: 8.7
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