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Pentax SMC DA 50mm f/1.8 Lens Review

Gary Wolstenholme reviews the new Pentax SMC DA 50mm f/1.8 prime lens on the Pentax K-5 Digital SLR.

| Pentax SMC DA 50mm f/1.8 in Interchangeable Lenses

Handling and Features

Pentax SMC DA 50mm f/1.8 Lens Review: Pentax SMC DA 50mm f/1.8

This standard 50mm lens sports a fast f/1.8 maximum aperture, ideal for blurring backgrounds, or for shooting in low light conditions. However, unlike many 'nifty-fifty' lenses, this optic carries a rather high £250 price tag. Is it worth the extra over equivalents from other manufacturers? We'll take a closer look to ascertain if it is.

Pentax SMC DA 50mm f/1.8 Handling and Features

Pentax SMC DA 50mm f/1.8 Lens Review: PenPentax SMC DA 50mm f/1.8 with Pentax K-5
The weight and dimensions of this lens are fairly typical for a lens of this specification. It weighs only 122g and protrudes 38.5mm from the lens mount. It makes a good lightweight companion for the Pentax K-5 body used for testing. Very high quality plastics have been used for the lens barrel, and the lens mount is plastic, which may put a few people off, especially if they change lenses very often.

Focusing is performed within the lens barrel with the entire group of elements moving back and forth inside. This design means that the lens does not extend during focusing and that the filter thread does not rotate, making it perfect for use with polarising and graduated filters. The 52mm is very common, so it shouldn't be too difficult to pick up accessories to fit. The manual focusing ring rotates during auto-focus, and isn't very well recessed, so care needs to be taken in use to ensure it doesn't catch your fingers. Manual focusing action is smooth, and well damped.

No distance scale is provided, or hyper-focal scale, which is a shame. The Pentax 'Quick Shift' focusing system has been implemented on this lens, which means manual adjustments can be applied once the lens has focused automatically.

Although focusing is screw-driven, it locks onto subjects very quickly. The older screw-driven system does generate more noise than newer silent focusing lenses do though. Despite the noise, focusing is swift and accurate, which makes the bright f/1.8 aperture very useable.

The minimum focus distance of 45cm is fairly typical for this kind of lens. A maximum magnification of 0.15x is possible, which may not be best suited for frame filling close ups images of small subjects.

Pentax SMC DA 50mm f/1.8 Lens Review: Pentax SMC DA 50mm f/1.8




Pentax SMC DA 50mm f/1.8 Performance

At maximum aperture, sharpness in the centre of the frame is already very good, with clarity towards the edges of the frame reaching good levels. Stopping down improves sharpness across the frame with peak performance being realised at f/5.6, where sharpness in the centre is outstanding, and excellent clarity is attained towards the edges of the frame.

Pentax SMC DA 50mm f/1.8 Lens Review: MTF at 50mm
MTF at 50mm

How to read our charts

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-5 using Imatest.

Chromatic aberrations are incredibly well controlled, barely registering in Imatest until the lens is stopped down beyond f/8. This very low level of fringing should pose no issues, even in large prints, or harsh crops from the edges of the frame.


Pentax SMC DA 50mm f/1.8 Lens Review: CA at 50mm
CA at 50mm

How to read our 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-5 using Imatest.

Falloff of illumination towards the corners is also well controlled for a lens with a fast f/1.8 maximum aperture. At f/1.8 the corners are only 1.15 stops darker than the image centre and visually uniform illumination is realised with the lens stopped down to f/4 or beyond.

Only a very slight amount of barrel distortion is present in images taken with this lens. Imatest detected 0.505% barrel distortion, which will be very hard to spot, unless straight lines very near the edges of the frame run absolutely parallel with the frame border. The distortion pattern is uniform across the frame, so if you require absolutely straight lines, this low level of distortion should be relatively easy to correct.

During testing, this lens proved itself quite resistant to flare and contrast levels remain good, even when shooting into the light.

Pentax SMC DA 50mm f/1.8 Sample Photos

Value For Money

With a price tag of around £250, the performance of the optics are certainly worth paying a little extra for, although some aspects of the lens' design bring how good value this lens is into question. For example the plastic lens mount is a feature normally seen on much cheaper lenses.

Pentax also produce a 50mm f/1.4 lens, which sports a faster maximum aperture, but costs £330 as a result. Those looking for a lens around this focal length, who have money to spare, may also consider the Pentax 43mm f/1.9 Limited lens, which costs around £780.

Sigma also produce a 50mm f/1.4 which is available with a Pentax K mount fitting for around £380.

Pentax SMC DA 50mm f/1.8 Verdict

The optical performance of this lens is excellent, which makes it well worth the £250 asking price, even if this does seem a little steep for a 50mm f/1.8 lens with a plastic lens mount.

Overall this lens delivers sharp results at every aperture, and is reasonably well built. However, a metal lens mount would normally be expected for a lens of this type at this price point and would allay any fears about the build of the lens.


  Pentax SMC DA 50mm f/1.8 Lens Review:
  The optical performance of this new lens is excellent, and well worth the money.

Pentax SMC DA 50mm f/1.8 Pros

Excellent sharpness from maximum aperture
Good build for the lens barrel
Fast focusing
Virtually no CA or distortion

Pentax SMC DA 50mm f/1.8 Cons

A bit on the pricey side for a 50mm f/1.8
Plastic lens mount.



Pentax SMC DA 50mm f/1.8 Specifications

Lens Mounts
  • Pentax K SMC-DA
Focal Length50mm
Angle of View47°
Max Aperturef/1.8
Min Aperturef/22
Filter Size52mm
35mm equivalent76.5mm
Internal focusingNo Data
Maximum magnificationNo Data
Min Focus45cm
Box Contents
Box ContentsNo Data

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4 Oct 2012 11:22PM
It's an interesting lens and a worthy addition to the Pentax Line-up of small primes.
I am not worried about the plastic mount, I have the 35mm f2.4 which is the same. Is it a problem? Not at all, it is robust and the lens being so light, not an issue.
Now Pentax have a plethora of lenses within a tight focal range to suit all needs.
We now have
DA-50mm F1.8 - Budget but with typical Pentax optics, ie sharp!
FA-50mm F1.4 - Older lens, but until you stop down to F2, it is lacking contrast and CA is troublesome
DA-40mm F2.8 - The Pancake, tiny lens, not fast, but oh so sharp!
FA-43mm F1.9 Limited. Not used one, but very well regarded indeed.

It will be nice if Pentax's next lens will be the FA-50mm F1.4 mk2, sorting the issue of contrast and CA wide open. If they can add an AF clutch too and keep the Aperture ring, then I am sold.
In the meantime, I will use my 40mm Limited and FA50, but seriously consider the DA50 for contrasty wide open shots.Smile
theorderingone 19 2.4k
5 Oct 2012 1:01PM
The plastic mount is not necessarily a problem, but it can be an issue if you treat your gear roughly.

When I used to work in photographic retail, I would often see lenses with plastic mounts brought in for repair, as the lens has detached from the mount after being dropped/knocked.

The main culprits were Canon 50mm f/1.8s and Nikon 18-135mm lenses, both with plastic mounts.

Like I said. Not necessarily an problem, but it is something to be aware of.

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