Bokeh

Bokeh is hard to quantify or even test in a controlled manner. But taking a look at the rendition of out-of-focus highlights near and far from the focal plane can give us a good indication of what to expect. Here's we're comparing how the two lenses render defocused city lights as we focus beyond, and in front of, the plane of focus.

Immediately, it's obvious that the 50/1.4 has less of an onion ring effect (a tell-tale sign of aspherics) compared to the 55/1.8. This helps the 50/1.4 render more natural out-of-focus highlights, which gives it a leg up in portraits like this.

However, somewhat surprisingly, the FE 55mm bokeh looks a little smoother, at least when the city lights are slightly behind the plane of focus (when we're focused closer than infinity). Let's take a look at why this might be: note the soap bubble bokeh the 50/1.4 displays when examined at 1:1 relative to the 55/1.8. While arguably quite pleasing, the extra detail in the rims of out-of-focus regions interfere, which detracts a bit from the smoothness of blur.

Interestingly, for objects in front of the focus plane (foreground objects), the differences appear minimal at best, and it appears this is due to the 55/1.8 gaining some soap bubble-like character in addition to its onion-ring bokeh. In fact, the 50/1.4 has the edge here, because at least it lacks the severe onion-ring effect of the 55/1.8.

The bokeh differences become minimal when the city lights are far behind the plane of focus. This is to be expected - significant defocus diffuses any patterning in the bokeh, which is why it's hard to detect significant bokeh differences between lenses in close-up portraits with distant, defocused backgrounds. Far more telling is what happens with slightly defocused objects in front of, and behind, the focal plane, as we've done above.

To sum up...

Overall, bokeh is very pleasing from both lenses, as one would expect with any fast prime of this focal length. Some photographers may prefer the slight soap bubble effect of the 50/1.4, even though it may come at a slight cost in smoothness of bokeh near the focal plane. In our opinion, the lack of severe onion-ring effect gives a leg up to the newer 50/1.4.

Longitudinal Chromatic Aberration

The bokeh comparison above tells us something else about the lenses as well: the 50/1.4 has considerably less longitudinal chromatic aberration (CA) than the 55/1.8. Note less green fringing as well as purple fringing behind, and in front of, the focal plane (refer to widget above as you click these links). The relatively low levels of axial CA is also evident in real-world photographs: for example, purple and green fringing in the black lettering in front of, and behind, the focal plane, respectively, are very well-controlled in the image below. Usually this sort of fringing is exceedingly easy to spot on high-contrast lettering such as the '4' below, yet it's largely absent with this lens.

In fact, you'll generally note a lack of such fringing in all our images from the 50/1.4 sample gallery, and the same cannot be said for the FE 55/1.8. This is important, as axial CA plagues fast primes with aspherical elements, and is fairly difficult to remove in post-processing. A fair number of the most compact FE lenses, like the 55/1.8 and the Batis 25/2 are notorious for their levels of longitudinal CA, and we're quite pleased to see how well it's controlled on the 50/1.4.

Coma

Below, we take a look at coma (the spread of point sources at edges) performance of the two lenses, at apertures ranging from wide-open to F4 (beyond F4, coma tends to minimal on most lenses). The 50/1.4 takes the lead here, showing barely any coma at all even wide open, while the 55/1.8 needs to be stopped down to F2.8 before edge highlights appear circular (which is still quite respectable performance). There's some slight coma on the left with our copy of the 50/1.4, but it's gone by F1.8. The 50/1.4 also avoids odd - but kind of cool - artifacts like this.

Summary

The new Sony FE 50mm F1.4 ZA is impressive. Our friend Roger Cicala over at LensRentals notes its central sharpness performance to exceed even the venerable Zeiss Otus, as well as the Sigma 50mm Art. He even found it to out-perform the 55/1.8 centrally, but fall behind it peripherally. Our results show the 55/1.8 to slightly pull ahead wide open both centrally and peripherally, with the 50/1.4 pulling ahead in central sharpness by F2.8. We'll look into nailing down the source of this discrepancy (it's always possible our copy of the 50/1.4 was slightly decentered), but sharpness performance between the two is comparable, and the 55/1.8 was already one of the most respected normal primes with respect to sharpness.

Therefore, we feel it fair to say the FE 50/1.4 pulls ahead of most, if not all, normal prime offerings from competitors (though we'd imagine the Sigma 50mm Art to put up a good fight). Despite a severely off-center composition, take a look at the tack-sharp eye of our model below, shot at F1.4.

Sharpness isn't everything of course, and in other respects, the 50/1.4 also impresses. Bokeh is pleasing, with very little onion ring effect, particularly compared to the 55/1.8. There is a slight soap-bubble effect to bokeh though, which may be pleasing to some, but can cost some smoothness in out-of-focus regions (but if it does, it's certainly not easy to spot in any of the portraits in our gallery). Longitudinal CA is impressively well-controlled, to the point where you won't notice much purple or green fringing near the focal plane even when shooting wide open. Nighttime cityscape and astro-photographers rejoice: coma is nearly non-existent even wide open. Videographers will appreciate the de-clickable aperture ring.

It's clear that Sony is trying to cement itself as a real option for pros, and the new FE 50mm ZA helps further that goal. We have no reservations recommending this lens. That said, if you can spend the extra time processing out the axial CA in post, don't mind onion-ring bokeh in out-of-focus highlights, aren't bothered by coma, and don't need the extra isolation or light-gathering capability of F1.4, the 55/1.8 is a compelling alternative that is lighter and cheaper, while offering smooth background bokeh and impressive, if not necessarily much greater, sharpness wide open. It also focuses significantly faster than the 50/1.4.* But for subject isolation that puts medium format to shame, while retaining respectable sharpness and contrast even far off-center wide open (and particularly by F2), the FE 50mm 1.4 ZA is the lens to own.


* The FE 50mm F1.4 ZA, like most recent Sony lenses, focuses stopped down at your selected aperture. This means that autofocus performance steadily drops as you stop down, since smaller apertures mean less light, and more depth-of-field (less phase difference) for the autofocus system to work with. By F9, phase-detect fails altogether, and you'll experience significant hunting in AF-C.

While the intent is to minimize focus shift and shutter lag, ironically you may experience an increased lag in shooting due to decreased AF performance when shooting at smaller apertures - particularly relative to the 55/1.8 which already focuses faster due to a smaller focusing group and potentially faster motor.

While we continue to express our disappointment at this focus behavior to Sony (we'd like to see the lens always remain wide open during live view, only stopping down to take the shot, with focus shift look-up tables for lenses exhibiting severe spherical aberration), we encourage you to let your thoughts regarding stop-down focusing known in the comments below.