Pentax has modernized most of its lens lineup for the APS-C sensor size, but kept a handful of older full-frame optics in production. The Pentax SMC FA 50mm F1.4 ($274.95) is one of them, and unfortunately its optics haven't stood the test of time. It delivers very soft performance at wide apertures, especially when paired with a modern 36MP sensor like the one you find in the K-1. If you want a standard-angle prime, consider instead the FA 43mm Limited, an Editors' Choice winner, or wait until the promised 2018 release of the Pentax HD D FA* 50mm f/1.4 SDM AW.

Design

The FA 50mm ($314.27 at Amazon) is a tiny lens by modern standards, measuring just 1.5 by 2.5 inches (HD) and tipping the scales at 7.8 ounces. The black barrel is polycarbonate and relatively free of adornments. The front element supports 49mm filters and the lens does not ship with a hood.

There's a physical aperture ring, so you can use the lens with a vintage film camera. I put it to the test and ran a roll of film through my 1980s-era Pentax LX, something you can't do with more modern lenses that rely solely on electronic aperture control. The ring can be set to its A position for use on a digital camera, offering third-stop adjustments. When adjusted manually it can be set at f/1.4, f/2 through f/11 in half stops, and to f/16 or f/22.

Autofocus is driven by a screw-drive system, so it's on the noisy side. The focus throw is short, so focus is quick. Quick shift focus is not supported, which means you need to set your camera's AF/MF switch to the the MF position if you want to make any manual focus adjustments.

The lens focuses as close as 18 inches (45cm), which gives it a rather paltry 1:7 macro magnification ratio. It's not atypical for a lens of this type, but we've seen others that focus closer, including the Tamron SP 45mm f/1.8, which sports a solid 1:3 macro capability. But unfortunately Tamron and Sigma have dropped support for Pentax with recent lens releases. If you want a close-focusing 50mm for the K-1, the SMC D-FA Macro 50mm F2.8 is currently your best option.

There's no weather sealing. That's to be expected from an older lens design—it's a feature that Pentax didn't start adding to its cameras until well after the 50mm F1.4 was released. There's also no optical stabilization, which is not a surprise as Pentax cameras have that feature built into the body.

Image Quality

When paired with the 36MP K-1 , the FA 50mm F1.4 produces very soft results at its widest aperture settings. At f/1.4 it scores only 1,109 lines on our standard sharpness test. That's less than half the 2,250 lines we want to see at a minimum from the K-1. The real-world result: images have a blurry, soft focus look at f/1.4. There's less softness at f/2, but not a lot less. The score is 1,580 lines there.

At f/2.8 things change dramatically. Details are crisp as the average score jumps to 2,288 lines. Edges are still soft, 1,448 lines, but depth of field will blur them away in many photos. The lens gets sharper and sharper as you stop down. It scores 2,413 lines at f/4, with decent edge performance, and starts to deliver crisp edge-to-edge images at f/5.6 (2,655 lines). It's at its best at f/8 (2,807 lines), and only loses a little bit of resolution at f/11 (2,776 lines), f/16 (2,615 lines), and f/22 (2,404 lines).

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The lens shows about 1.4 percent barrel distortion, drawing straight lines with a slight outward curve. That's not atypical for a 50mm f/1.4 design, and pretty easily corrected if you have your druthers. JPG shooters can enable an in-camera correction, and it's a relatively simple matter to straighten lines in Raw images if you use Lightroom for processing.

The same is true for the natural vignette that the lens draws around subjects. At f/1.4 the corners lag behind the center by about 3 stops (-3EV), and they show a -1.7EV drop at f/2. (At narrower apertures the difference in illumination is negligible.) If you shoot in JPG format you can set the K-1 to compensate automatically, and the same correction that removes distortion from Raw images in Lightroom brightens the edges of the frame.

Conclusions

Some vintage lens designs manage to deliver strong performance on modern high-resolution digital sensors. The Pentax SMC FA 50mm F1.4 isn't one of them, unfortunately. It delivers results that are positively soft focus at f/1.4 and f/2. It gets a lot sharper at narrower apertures, but if you're buying it to shoot at f/2.8, you may as well opt for the D-FA Macro 50mm F2.8 ($316.95 at B&H Photo Video) instead. Our favorite wide-aperture, standard-angle prime lens for the Pentax system is still the pricier FA 43mm F1.9 Limited ($546.95 at Amazon Canada) . There's a new 50mm f/1.4 due out this year from the company, part of its top-end FA* series. We'll see how it performs when it's released, but we do expect it to sell at a significantly higher price than the FA 50mm F1.4.

Pentax SMC FA 50mm F1.4 2.5 See It $314.27 at Amazon MSRP $274.95 Pros Very small.

Affordable.

Sharp when stopped down.

Aperture ring for film use. View More Cons Soft results at f/2 and wider.

Omits weather sealing.

Screw-drive focus system. The Bottom Line The Pentax SMC FA 50mm F1.4 lens struggles to keep up with modern high-resolution cameras.

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