A new day and a new quick test. This time around we're gonna take a look at the UWA lenses for the NEX system. Sony E 16/2.8 was one of the first lenses introduced along the NEX cameras and so far is the widest lens available for the E mount. SLR Magic announced that it will start manufacturing its HyperPrime 12mm f/1.8 lens for the NEX camera, but so far it has been just waporware and the lens is not available anywhere in the world. Sigma's 19/2.8 EX DN is the only other wide angle lens for the NEX cameras and marks Sigma's official entrance into the race. We recently saw how well Sigma's other NEX lens, the 30/2.8 EX DN performed against its Sony competitor, the E 30/3.5 Macro, so obviously there is a tremendous interest in the 19mm lens as well. Can Sigma deliver better performance at a better cost again?
Before we begin, and before you flood us with thousands of messages, let's be clear that this is not really an apples to apples comparison - you can't compare a 16mm lens to a 19mm lens. Well, you can - that's what we're doing here obviously, but the comparison is biased in a couple of ways. Firstly, a 16mm lens is wider and hence at the same focusing distance will have different EFOV and different DOF. To solve the EFOV problem, we used a larger target with the 16mm lens, which placed the measurement areas roughly into the same place as with the 19mm lens. But only roughly - we can say that we measured MTF50 in the corners for both lenses, but the points of measurement were different between the two lenses - the variance of 10% in true distance from the image center to the corner points of measurement between the two lenses is quite probable. We can't obviously do anything about the DOF difference, so we just ignored this issue. Secondly, we can't really do anything about the variance in optical characteristics of lenses that can arise due to the difference in the true FL - for example we can't compensate for distortion to measure true resolution, so again, we simply ignore this. But not everything in this test has as much variance - vignetting and lateral CA measurements are, for example, more comparable than say raw MTF50.
So why are we doing this comparison, knowing all in advance that this is an apples to oranges comparison? Curiosity, which as they say, 'killed the cat' (please note that no cats or other animals were actually used or hurt in this test). More importantly, this test can give the foundation for intuitive guesses that many practitioners have been expressing in online forums - after all, if it looks like a duck and quacks like a duck, it's most likely going to be a duck. And so with that...
Booyah! Sigma floors Sony's lens to the ground in this department. Both lenses show more or less comparable resolution in the center - Sigma is a little bit better across all apertures, but most notably at f/2.8. But corner performance is just a no-compatition at all - the variance between the two lenses is 20% to 50% across the apertures.
And Sigma wins this bout as well, showcasing a significantly lower lateral CA across the aperture than Sony E 16/2.8. The difference is astounding - ~1.5px on average. Less CA = very good in our books, although it's hard to translate the raw lateral CA numbers that Imatest produces into the visible amount of artifact that users would experience in their rints.
Uncorrected vignetting is slightly worse on Sigma - the difference is small in absolute terms and may or may not be visible in real life.
Unfortunately, distortion is not quite comparable between these two lenses - Sony's 16mm/2.8 shows mild wavy distortion, which fools Imates into thinking that the lens has a pincushion distortion. On the other hand, Sigma's 19/2.8 shows a plain barrel distortion, albeit very small. So take it as it is - mild wavy vs mild barrel.
And we have a winner - surprise, surprise, it's Sigma again. Its raw resolution around borders, as well as better lateral CA, earned it the victory in this round. Vignetting can be considered a wash, while Sigma's distortion is easier to correct. And so unless you really need those extra 3mm of FL (actually 4.5mm in EFOV), than there is no reason why you'd want to buy Sony's lens - it's just plain worse in pretty much every asect. And on top of that, more expensive. From practical perspective, there is not that much difference between EFOV of 24mm and an EFOV of 28mm (for 16mm and 19mm lenses respectively) and so Sigma becomes our preferred choice in this quick test...