January 2009 | Margaret Brown
A lightweight standard zoom kit lens for Pentax DSLR cameras.
RRP: $399.95 (when purchased separately)
Rating (out of 10):
- Build: 8.0
- Handling: 8.5
- Image quality: 8.0
- Versatility: 8.5
- OVERALL: 8.0
The smc Pentax-DA L 18-55mm f/3.5-5.6AL lens supplied for us to review with the K-m camera body was not quite the same as the lens that is sold as a stand-alone item and shown on Pentax's website. There was no green band on the review lens and no focus markings in front of the focusing ring and, although the dimensions of the review lens matched those of the lens listed on the Pentax website, it appeared to be less refined.
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The smc Pentax-DA L 18-55mm f/3.5-5.6AL lens supplied for us to review with the K-m camera body was not quite the same as the lens that is sold as a stand-alone item and shown on Pentax's website. There was no green band on the review lens and no focus markings in front of the focusing ring and, although the dimensions of the review lens matched those of the lens listed on the Pentax website, it appeared to be less refined.
Photo Review felt it was fair to review the kit lens because it's the one most people will acquire when they purchase one of Pentax's DSLR cameras. A compact standard zoom lens, it is designed for cameras with 'APS-C' sized image sensors, where it covers focal lengths from 27.5 to 84.5mm in 35mm format. Both the barrel and the lens mount are made from rigid plastic, which accounts for its relatively light weight.
Published specifications for the DA 18-55mm f/3.5-5.6AL II lens show it to consist of 11 elements in 8 groups with one aspherical element and one super-low dispersion glass element to minimise a range of aberrations. Autofocusing relies on a slotted drive screw, which is controlled by the camera body. This means noticeable focusing noise in AF mode - a factor we observed with the review lens.
Six diaphragm blades close to produce a near-circular iris. Optical surfaces appear to have been coated to reduce flare and ghosting but we have no information on the nature of these coatings.
The zoom ring is closer to the camera body. It's approximately 28 mm wide with a 15mm wide, deeply-ridged grip. The trailing edge carries engraved marking for the 18mm, 24mm, 35mm, 45mm and 55mm settings.
Just in front of the zoom ring is a 10mm wide focusing ring with a 5mm wide finely-ridged grip on its trailing edge. A bayonet moulding around the front of the lens appears to be designed for the lens hood and there's a white mark for lining it up when it is fitted.
The front of the lens is threaded to accept 52mm filters. The only accessories supplied with the review lens were end caps. However, the lens listed on Pentax's website comes with a petal-shaped lens hood.
Handling
The supplied lens was a good match in both size and weight for the K-m body. However, its plastic mount sounded a little rough when we attached it to the camera's metal mount. Moving through the zoom range requires just under a quarter of a turn and we found the markings on the lens barrel corresponded reasonably well with the actual focal length settings.
The lens barrel is at its shortest at the 35mm focal length setting and extends by approximately 5mm at the 18mm and 55mm positions. Internal focusing allows angle-critical filters to be used without requiring constant adjustments.
The focusing ring rotates through about a quarter of a turn when manual focusing is selected. In AF mode, it is lightly locked and you can hear a slight grating noise if it is moved. According to the published specs for the Pentax-DA L 18-55mm f/3.5-5.6AL lens, manual focusing is partially supported in AF mode via a "Quick-Shift Focus System" that allows manual fine-tuning of focus settings. Fortunately, it's seldom necessary.
Both the zoom and focusing rings moved quite smoothly and positively and we found no evidence of zoom creep when carrying the camera facing downwards. No zoom lock is provided.
Performance
For a budget-priced lens, the supplied lens turned in a creditable performance, although overall contrast was relatively low and shots looked a little less 'snappy' than we'd like. Fortunately, ramping up the contrast with an image editor went a long way towards solving this problem.
In our Imatest assessments we found the test lens performed best at wider apertures, tailing off from about f/8 onwards where diffraction began to impact on image sharpness. Interestingly, the 35mm focal length setting gave the highest resolution, peaking at f/9.5. At wide aperture settings the lens suffers from low contrast and edge softening but this is largely resolved by f/8. We wouldn't recommend using this lens at apertures smaller than f/11. The graph below shows the results of our tests, based on JPEG images.
Lateral chromatic aberration was surprisingly well controlled with negligible CA at the 35mm, 45mm and 55mm focal lengths and low CA at 24mm. CA drifted into the 'moderate' band with the 18mm setting but only just. Few standard kit zooms match this performance. The graph below shows the results of our Imatest tests.
The red line marks the border between 'insignificant' and 'low' CA, while the green line is the boundary between 'low' and 'moderate'.
Like many kit zooms, the Pentax lens showed noticeable barrel distortion at the 18mm setting. However by 35mm the lens was almost distortion-free, although slight pincushioning was observed at 55mm. The review lens suffered less from vignetting than we expected and only slight corner darkening was seen in shot taken at the 18mm focal length at f/3.5. By f/5.6 the effect had vanished.
Buy this lens if:
- It's bundled with a Pentax camera and, therefore, represents good value for money.
Don't buy this lens if:
- You take a lot of backlit shots.
- You prefer 'punchy' images straight from the camera.
- You're hard on equipment. (Because of its lightweight construction, this lens won't tolerate rough handling.)
IMATEST GRAPHS
SAMPLE IMAGES
18mm focal length, 1/180 second at f/6.7.
55mm focal length, 1/125 second at f/6.7.
Vignetting; 18mm focal length, 1/1500 second at f/3.5.
Flare; 30.6mm focal length, 1/325 second at f/4.
Close-up at 18mm; 1/90 second at f/8.
Close-up at 55mm;1/80 second at f/8.
37.5mm focal length, 1/90 second at f/5.6.
55mm focal length, 1/30 second at f/9.5.
32.5mm focal length, 1/60 second at f/8.
24.4mm focal length, 1/250 second at f/8.
Additional sample images can be seen in the review of the Petnax K-m DSLR camera.
Picture angle: Equivalent to 27.5-84.5mm in 35mm format
Maximum aperture: f/3.5-5.6
Minimum aperture: f/22-38
Lens construction: 11 elements in 8 groups
Lens mount: Pentax K-AF
Diaphragm Blades: 6
Minimum focus: 25 cm
Maximum magnification: 1:3
Filter size: 52mm
Dimensions (Diameter x L): 68 x 67.4 mm
Weight: 220 grams