Sony has announced a high-end 'normal' prime for its Alpha E-mount line of cameras: the Planar T* 50mm F1.4 ZA lens. As the third normal prime for the system, we wanted to know what it offers over the already excellent FE 55mm F1.8 ZA, so we set about performing some benchmark tests.

We'll take a look at sharpness on this page, and bokeh, coma, and longitudinal chromatic aberration on the next.

Sharpness

Below, you'll see a series of aperture progressions for the 50mm F1.4 ZA and 55mm F1.8 ZA. Have a look around the scene at various apertures to get an idea of the capabilities of these two lenses - with the caveat that this performance is only representative of our single copy of each lens.

Wide-open, the 55/1.8 is slightly sharper than the 50/1.4, both centrally and peripherally (the advantage is retained on the left side of the frame as well, despite the fact that our 55/1.8 is slightly decentered and has poorer left side performance). But none of this should be too surprising, since sharpness at F1.4 is far more challenging than at F1.8. In fact, the 50/1.4 holds up very well considering the 2/3 EV disparity in f-stop.

Comparing both lenses at F1.8 (a more level playing field), the 50/1.4 catches up to the 55/1.8 in terms of center sharpness, but still lags in peripheral sharpness on the left and right sides of the frame. By F2, though, the 50/1.4 just surpasses the 55/1.8 in central sharpness, though off-center it still lags a bit. By F2.8 though, the 50/1.4 pulls ahead of the 55/1.8 even here off-center, and particularly at center where it pulls and stays ahead at higher F- numbers. Peripherally, though, the 50/1.4 never quite catches up to the 55/1.8, not at F2.8, and not even by F5.6 (the lenses are a bit more even on the left side at F2.8 and F5.6 due to the weaker performance of our 55/1.8 on the left but, technically, the F1.4 is still a little bit behind).

What does this mean?

The new 50/1.4 ZA displays impressive sharpness and contrast at F1.4. Our copy didn't hold up as well as the 55/1.8 wide open, but displayed particularly respectable performance considering the 2/3 stop light and depth-of-field advantage. These new lens designs deliver sharp and punchy images wide open, instead of the soft and hazy images you may be used to getting if you slap on old F1.4 designs on such high resolution sensors (remember that we're using the unforgiving 42MP a7R II for this test).

That said, the new 50/1.4 does not retain this sharpness across the field as well as the 55/1.8, which offers better field uniformity at all apertures. By F2, though, the new 50/1.4 ZA matches the 55/1.8 in central sharpness, and surpasses it at all smaller apertures. Considering the high bar set by the 55/1.8 ZA, this is very impressive. However, you give up off-center sharpness at the widest apertures. If we were forced to pick an overall winner here in terms of sharpness, we'd probably go with the 55/1.8, but really there isn't a huge difference between the two, particularly when you factor in the realities of copy variation.

Roger Cicala over at LensRentals found the Sony 50mm F1.4 lens to be the sharpest centrally of any 50mm prime, outperforming the 55mm F1.8 ZA. However, peripherally, the 50/1.4 takes a plunge in terms of resolution, and the 55mm F1.8 pulls ahead. In fact, just 4mm out from center in the image circle, tangential resolution (which we assess by considering the highest frequency MTF trace: 50 lp/mm) drops below that of the 55/1.8 (solid purple line). Source: LensRentals Blog

It's worth noting that Roger Cicala at LensRentals found the central sharpness wide open of the 50/1.4 to exceed the 55/1.8 (see MTF traces above), while our visual results don't show the 50/1.4 to exceed the 55/1.8 until F2.8. We can't rule out the possibility that our copy of the 50/1.4 slightly under-performed relative to the average, perhaps due to decentering; however, it's reassuring that he found the 55/1.8 to offer greater uniformity. This difference in peripheral sharpness may be the reason for the apparent discrepancy in our results, though copy variation is also highly likely to play a role (note that the worst performing 50/1.4 Roger tested was significantly worse than the best 55/1.8).

To elaborate, below we show our infinity scene overlaid with red and blue rings representing image heights of 4mm and 16mm, respectively: the two points where the 50 lp/mm MTF traces of the two lenses intersect. Between these rings, Roger's 50/1.4 tangential 50 lp/mm trace falls below the 55/1.8. Hence, our visual shootout seems to agree with Roger's results: aside from a very small region in the center, the 55/1.8 does outperform the 50/1.4 wide open (though we don't see the improvement towards the edges of the 50/1.4 that Roger sees: our 55/1.8 remains ahead peripherally). And, again, we may have tested a copy that under-performs relative to the average, which Roger's data is more representative of.

Our infinity scene with red and blue rings that represent 4mm and 16mm image heights (distance from center in the image circle). Between these regions, Roger's own MTF data indicate a dip in tangential resolution. It may only be a small region in the center (within the red circle) where the 50/1.4 significantly out-resolves the 55/1.8 wide open, which would explain the apparent discrepancy between Roger's results and ours. Copy variation is also likely to play a role in the differences - we only tested a single copy.

All that said, sharpness isn't everything. How does the new 50/1.4 fare in terms of bokeh, coma, and purple/green fringing? Let's take a look on the next page.