Sony recently updated its FE line, which now offers 16 full-frame lenses for Sony's E-mount Alpha cameras (not counting 3rd party options like the Zeiss Batis line, or Sony's wide/tele converters). Among the new lens introductions is the FE 50mm F1.8, what you might call Sony's 'nifty fifty'. We spent some time shooting with it in San Francisco this weekend, paired with the unforgiving 42MP of the Alpha 7R II. Click on the image above and see how the lens holds up in our real-world samples gallery, and have a read of some of our initial thoughts, after the break, below.

Initial impressions

We were definitely pleased to see a lower cost full-frame FE lens from Sony - particularly a fast one. The Sony/Zeiss FE 55mm F1.8 retails for $998, and although it's incredibly sharp and quick to focus, the cost may put off potential buyers. The new FE 50mm retails for a much more affordable $249.99. The lower price point does mean some tradeoffs, of course. Let's take a look at some of them below.

Optically Sony's new normal is a variant of the traditional double Gauss design. In fact, it appears very similar to the Canon 50mm F1.8 II design.

MTF performance graphs, however, indicate the lens should be sharper than the Canon's 50mm F1.8 II (the MTF curves for the new 50mm STM are, for the most part, almost identical to the Mark II) wide open, particularly in the center. Sharpness and contrast appear very impressive across the entire frame by F8.

Just don't expect Sony/Zeiss FE 55mm F1.8 levels of sharpness, which is able to maintain both contrast and resolution across the frame wide open considerably better than the new FE 50mm (Zeiss chooses to show 20 and 40 lp/mm performance as opposed to 30 lp/mm performance for the FE 55mm, but you can imagine 30 lp/mm as a trace in between the green and blue curves below). Astigmatism is also very well controlled in the FE 55mm.

There are some compromises when it comes to the FE 50mm lens focus-wise. It features a unit focus design with a DC motor, a first for a Sony FE lens, according to Sony engineers. Unfortunately, this does mean slower AF speeds and non-silent performance compared to Sony's linear actuator and Direct Drive SSM lenses (to be fair though, those lenses set a very high bar). On the other hand, Sony assures us that the unit focus design allowed them to achieve higher optical performance than they might have achieved with a smaller focus element - for this price point and size, anyway. 

Stop-down focusing

One thing in particular we should call out is that this particular lens does not open up its iris during AF acquisition (on an a7R II, and probably all other bodies), which means that focus speeds get slower and slower the more you stop down. Sometimes at smaller apertures in challenging light, focus can fail altogether, working again if you revert to a wider shooting aperture. This aperture dependence of focus is unfortunate, and somewhat crippling in some scenarios, sometimes forcing you to dial in F1.8, focus, switch to MF, then stop down and shoot. Sony says this is intentional design to avoid the extra time it takes to open and close the aperture during AF acquisition - a valid concern. Focusing at the shooting aperture also avoids any issues due to focus shift. While this makes sense, the slower AF speeds from trying to focus stopped down may be more crippling in some situations: the resultant decreased light levels and increased depth-of-field both serve to decrease focus performance and speed. Furthermore, any focus shift issues (1) become less of an issue the further you stop down due to depth-of-field, and (2) can be mitigated via look-up tables that correct for differences between optimal focus at the focusing vs. shooting aperture.

For its price point and size, the aforementioned trade-offs are certainly understandable, and many will appreciate the availability of a low-cost fast prime for the popular Alpha E-mount series. The lens is incredibly sharp by F4, and wide open performance is still very respectable centrally, and will appear even more so mounted to a more forgiving, lower resolution a7 camera. Sharpness and contrast can suffer peripherally wide open at 42MP (seen as a dreamy haloing of subjects near edges), but things sharpen up quickly as you stop down. And to be fair, 42MP. We do hope, though, that the stopped-down focusing results are improved via firmware changes that at least allow the option of forcing the lens to focus wide open. In fact, we'd prefer if the system simply worked more like a DSLR: keep the aperture open at all times, only stopping down to take the shot. After all, depth-of-field preview can always be used to preview the shooting aperture.