Pentax 50mm f/1.8 SMC DA

SLRgear Review
August 28, 2012
by Andrew Alexander

The Pentax-Ricoh 50mm ƒ/1.8 DA lens was announced in May of 2012, becoming available for purchase in July. Pentax has had a long-standing ƒ/1.4 version of the 50mm lens since its days with 35mm film bodies, but this lens has been discontinued for some time. (Note: at the time of writing, a large stock of the 50mm f/1.4 still exists for purchase.)

The 50mm ƒ/1.8 DA was designed for use with Pentax-Ricoh's APS-C digital camera bodies, offering an equivalent field of view of around 75mm in 35mm film terms. The lens takes 52mm filters and is available now for around $250.

Sharpness
When used wide open on the Pentax K-5 body, the 50mm ƒ/1.8 DA did not produce exceptionally sharp images: there is a generalized softness across the frame at ƒ/1.8 or ƒ/2. At ƒ/2.8 there is a great improvement in image sharpness, which gets steadily sharper (though with increasingly marginal returns) as the lens is stopped down to ƒ/8. At ƒ/8, the lens offers tack-sharp images.

Diffraction limiting is technically evident at ƒ/11, but you'd be hard-pressed to note any real-world impact on image sharpness until the lens is stopped down to its smallest aperture at ƒ/22.

Chromatic Aberration
Looking at the Chromatic Aberration test results, you would assume the lens offers excellent tolerance to CA, and you would be right - lateral chromatic aberration is virtually non-existent with this lens. However, like many fast prime lenses, longitudinal (axial) chromatic aberration is quite noteworthy where the lens is used at ƒ/1.8: in our sample images you can see magenta fringing in almost every area of high contrast. This goes away as the lens is stopped down, and it should be something you can remove in post-processing.

Shading (''Vignetting'')
There is some slight corner shading when the Pentax 50mm ƒ/1.8 DA is used at the ƒ/1.8 or ƒ/2 aperture setting; the extreme corners are 1/3 EV darker than the center. At any other setting, there is no corner shading.

Distortion
Whether through design or in-camera post-processing, the Pentax 50mm ƒ/1.8DA produces almost no distortion to speak of (there is some very, very light barrel distortion).

Autofocus Operation
The Pentax 50mm ƒ/1.8 DA takes under a second to go through its focusing range, but it is very noisy, making a high-pitched noise when autofocus is used. The focus ring turns when in AF mode, so it's advisable to keep your fingers clear of the ring so you don't damage the lens. There is a noticeable clunk noise when the focus mechanism hits the closest or infinity stops. We were able to compare the focus noise with the Pentax 18-55 II kit lens: the kit lens is much quieter than the 50mm lens. The lens takes 52mm filters, which will not rotate during focus operations.

Macro
The 50mm ƒ/1.8 DA provides poor macro performance, with a maximum magnification of just 0.15x, and a minimum close-focusing distance of 45cm (around 18 inches).

Build Quality and Handling
It's safe to call this lens an "economy" lens - if there is any metal in here, it's not obvious. The body mount and filter threads are plastic, as is the shell. The aperture is made up of seven rounded diaphragm blades, which should produce nice out-of-focus elements. The lens itself is made up of six elements in five groups; the design is very simple, as the front element extends during focus operations. Happily this element doesn't leave the shell, so it's not in any real danger.

There are no control surfaces on the lens other than the focusing ring: if you want to manually focus, you have to select that option in the camera settings. The focusing ring is a ribbed plastic, about 3/8'' wide. There is a lot of play in the ring - about 180 degrees between the hard stops of close-focus and infinity - making manual focus quite useful.

It's possible to use the Pentax RH-RA lens hood on this lens: it's a rubber hood that screws onto the 52mm filter threads of the lens. The RH-RA is sold separately from the 50mm ƒ/1.8 DA.

Alternatives

Pentax 55mm ƒ/1.4 SDM SMC DA* ~$700
The Pentax 55mm ƒ/1.4 is substantially more lens than the 50mm ƒ/1.8, offering a much higher build quality and price tag. Optically, the 55mm ƒ/1.4 is head and shoulders above the 50mm ƒ/1.8, offering tack-sharp results at ƒ/2.8.

Pentax 35mm ƒ/2.4 AL SMC DA ~$250
Of course if you're actually looking for a 50mm field of view, then the 35mm ƒ/2.4 is a better choice on the APS-C camera bodies produced by Pentax-Ricoh. We haven't yet tested the 35mm ƒ/2.4, but with a similar build quality to the 50mm ƒ/1.8 DA, we suspect similar results.

Sigma 50mm ƒ/1.4 EX DG HSM ~$500
Sigma also offers a fast prime 50mm ƒ/1.4 lens in the Pentax mount. It's significantly sharper than the Pentax 50mm ƒ/1.8 DA, but also significantly heavier (505 grams versus the Pentax's 122 grams). Sigma also produces the 30mm ƒ/1.4 in an APS-C size in the Pentax mount.

Conclusion
There's not much to add that our tests don't already show: it's an inexpensive lens that fills a gap in Pentax's lineup. Stopped down, it provides excellent results for sharpness, but many people will be buying it for its ability to shoot at ƒ/1.8, where it offers only mediocre performance. If you need to shoot at wide apertures, you are better served with Pentax's more expensive options; if you are looking for a portrait lens that you'll stop down to at least ƒ/2.8, then this could be a good alternative for you.

Product Photos

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.