Laowa 105mm f/2 (T3.2) STF – Image quality
The true area of interest of this lens lies in its bokeh and out-of-focus qualities. Thanks to its long focal length and large aperture it’s possible to create beautiful bokeh in out-of-focus areas. Bokeh is rendered in a wonderfully circular fashion, and doesn’t show any outlining towards the edge at f/2, whereas stopping down to f/2.8 and f/4 sees the outlining effect become slightly more pronounced around the perimeter of highlight discs. Switching between the 14-bladed diaphragm and the eight-bladed aperture before comparing the results side-by-side revealed a subtle difference. To create the most satisfying circular bokeh users should experiment with both diaphragms, but take special notice that both rings should not be used together.
A study of our lab results shows the lens produces a reasonable level of sharpness in the centre at f/2, with the corners appearing only slightly softer. Centre sharpness improves at f/2.8, and peaks at around f/4-5.6. It remains high at f/16, but sharpness drops off a little at f/22 due to the inevitable softening effect of diffraction.
Corner sharpness is relatively unimportant with such a specialised portrait lens, where the subject is usually going to be composed towards the centre of the frame. It improves gradually as the lens is stopped down, peaking at f/8, but then tails off beyond f/16. The sweet spot between centre and corner sharpness on this lens is therefore found between f/5.6 and f/8. To create the shallowest depth of field, users will be tempted to use its maximum aperture, but I found some of my sharpest and best results were captured at f/2.8.
A study of our uncorrected raw files reveals corner shading at wide apertures. We measured the corners to be approximately 1.2EV darker than the centre of the frame at f/2, reducing to 0.6EV at f/4. Stop the lens down further and you’ll quickly find corner shading disappears and no longer makes itself known in real-world images.
Medium telephoto primes are well known for controlling distortion extremely well, and this lens is no different. Our distortion chart shows just how well the lens controls curvilinear distortion, rendering straight horizontal and vertical lines right towards the edge of the frame. Rigorous testing of the lens in high-contrast conditions also revealed how well it controls chromatic aberrations. Looking at raw files with all corrections turned off showed barely any hint of fringing along high-contrast edges, even when images were studied at 100% magnification in Adobe Photoshop.