Pentax 16-45mm f/4 SMC DA ED AL

Gary Wolstenholme takes a look at this standard zoom for Pentax digital SLR cameras, which provides a wide angle view equivalent to 24mm on a 35mm camera and a constant f/4 maximum aperture.

Sitting in the middle of Pentax's lens range, the 16-45mm offers a moderately bright aperture of f/4 throughout the zoom range and a useful wide angle field of view equivalent to 24mm on a 35mm camera. The lens costs around £230, which isn't too pricey for a marque lens of this specification. Above this in Pentax's lens range is the 16-50mm f/2.8, which can be bought for around £695. Apart from having a brighter maximum, this lens also sports Pentax's SDM silent focusing motor.

Suitable alternatives from third party manufacturers include Tamrons 17-50mm f/2.8, which has a brighter f/2.8 aperture throughout the zoom range, but costs around £330. Sigma's 17-70mm OS HSM has Optical Stabilisation you can see working through the viewfinder and a silent focusing moor, but cost about the same as the Tamron.

Pentax 16-45mm f/4 SMC DA ED AL: Handling and features
Much of the lens barrel on the 16-45mm is made of lightweight, yet high quality plastics that feel quite robust and rigid. The zoom mechanism works the opposite way to what you might think, with the lens being at its longest at 16mm, and its shortest just before 45mm. The supplied petal shaped lens hood clips onto the front of the lens and moves with the zooming action, which is unlike other lenses of this design where the lens zooms inside the hood, This means the hood won't be as effective as it could be at shielding the front element from extraneous light as it could be at 70mm.

The zoom mechanism is smooth and quite loose between 16mm and 35mm. For the last 10mm it tightens up a bit, but is still quite easy to adjust even here. I had no issues with zoom creep during use despite the zoom ring feeling quite loose.

Focus is powered by the screw-driven motor in the camera and is quite responsive and quick to obtain a lock in a wide range of condition on the K-7 used for testing. A full time manual focus feature allows the focus to be adjusted at any time, just like on lenses with silent focus motors, which is a nice addition.

Weighing only 365g, this lens is quite lightweight and at 92mm long it isn't too large either, which should make it an ideal companion for travelling photographers, or those who just wish to travel light.

Overall the lens feels well put together and responsive to focus. I really enjoyed using it due to this and the lightweight and compact design.

Pentax 16-45mm f/4 SMC DA ED AL: Performance
This lens performs well throughout the range, starting off strong at 16mm and getting good again at 45mm. At 16mm and maximum aperture the sharpness is already very good in the centre and the quality towards the edges is acceptable. Stopping the lens down improves the sharpness across the frame as far as f/8, where the resolution is excellent across the frame.

Zooming to 28mm causes a slight loss of sharpness at each aperture, but the quality at maximum aperture is generally more than acceptable. At f/4 the centre sharpness approaches good levels and the quality towards the edges is fair. Peak quality is achieved at f/11 where the sharpnes in the centre is very good and the quality towards the edges is good.

Finally at 45mm the sharpness in the centre at maximum aperture is already very good with good sharpness produced towards the edges. Here peak quality across the frame is achieved at f/8, where the resolution is very good across the frame.

Resolution at 16mm	Resolution at 28mm
Resolution at 45mm	How to read our graphs The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column. The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple. For this review, the lens was tested on a Pentax K-7 using Imatest.

Chromatic aberrations are well controlled with levels staying well below noticeable levels until 45mm. Here fringing increases at maximum aperture to around 0.9 pixel widths towards the edges, which may become noticeable in large prints with high contrast edges towards the edge of the frame.

Chromatic Aberrations at 16mm	Chromatic Aberrations at 28mm
Chromatic Aberrations at 45mm	How to read out charts Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software. Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more. For this review, the lens was tested on a Pentax K-7 using Imatest.

At 16mm falloff of illumination towards the corners is very well controlled. Here Imatest recorded a barely noticeable level of vignetting of 0.7stops. Stopping down to f/5.6 results in visually uniform illumination. This low level of falloff remains constant throughout the zoom, which is excellent performance for a lens of this type.

Distortion is also very well controlled. At 16mm Imatest recorded only 1.36% barrel distortion, which should only pose an issue in the most critical of applications. At 45mm Imatest could only detect 0.306% barrelling, which is amongst the lowest levels I have seen on a zoom lens. Unfortunately the distortion pattern isn't constant across the frame, so care will need to be taken correcting the curvature of lines if it does become an issue. Still with such a low level present I believe most people will be able to live with this.

Click on the thumbnails for a high resolution image.
In this shot taken at 16mm and f/8 you can see the excellent levels of sharpness across the frame.		And at 45mm the performance is still kept at a high level.

This lens is reasonably resistant to flare and ghosting. Strong point light sources in the frame will cause a slight loss of contrast and some flare, but not so much that the lens is unusable under these conditions. Light sources just outside of the frame may also cause flare if the supplied lens hood isn't fitted. This hood is a petal shaped type and it does an excellent job of keeping unwanted light off the front element.

DxOMark provides objective, independent, RAW-based image quality performance data for lenses and digital cameras to help you select the best equipment to meet your photographic needs. Visit the DxOMark website for tests performed on the Pentax 16-45mm f/4 SMC DA ED AL.

Pentax 16-45mm f/4 SMC DA ED AL: Verdict
This lens is generally a very good performer and it doesn't cost much either. In my mind this is the ideal standard zoom lens for use with Pentax digital SLRs if you don't require a faster aperture than f/4 or an obnoxious zoom range.

For the price the levels of sharpness are excellent. Coupled with the low distortion and low levels of colour fringing it makes the lens a very attractive prospect indeed.

An excellent all-round performer.

Pentax 16-45mm f/4 SMC DA ED AL: Pros
Good sharpness throughout the zoom range
Low distortion
Low CA
Excellent value
Good build quality

Pentax 16-45mm f/4 SMC DA ED AL: Cons
Uneven distortion pattern may be difficult to correct if necessary
CA increase at 45mm and f/4

FEATURES
HANDLING
PERFORMANCE
VALUE FOR MONEY
OVERALL

Pentax 16-45mm f/4 SMC DA ED AL: Lens specification

Price	£230.00
Contact	www.pentax.co.uk
Filter size	67mm
Format	APS-C
Construction	13 elements in 10 groups
Angle-of-view	83 - 35 degrees
35mm equivalent focal length (on APS-C body)	24 - 67.5mm
Internal focusing	Yes
Image stabilisation	No (Pentax Stabilisation system is in body)
Minimum focus	28cm
Maximum aperture	f/4
Minimum aperture	f//22
Weight	365g
Size	92 - 72mm
In the box	Front cap Rear cap Lenshood

The Pentax 16-45mm f/4 SMC DA ED AL costs around £230 and is available from Warehouse Express here:

Pentax 16-45mm f/4 SMC DA ED AL

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