Resolution (A7R) This was less clear than I had expected, partly because I saw quite different results (at the edges) in this more controlled test than in my informal preliminary tests. These shots were made at close to the infinity stop (about 50m in reality), whereas my initial tests were focused at perhaps 12-15m and I suspect this has made quite a difference. I hope to better understand and explain this in the very near future, but will report the result that I have at this stage. …So at 50m focus: As a family, the Zuiko wide-angle lenses have slightly higher central resolution. The OM 24 just tops the FDn 24mm on centre and the same is true for both the OM 28 f2.8 and f3.5 vs the FDn 28mm. Its not a massive difference, but can clearly be seen at 100% with images in the f4-f8 realm; however with the A7R that’s a 74” print. At 50% or 1:2 the difference disappears, so you are going to have to make some large prints to see a difference in the flesh so to speak. There may be a little more sparkle with the OMs on centre, where you perceive a slight difference more than you actually see it if you try to ‘find it’. So, with the OMs you gain a bit of resolution, but have a little less contrast. Its also worth noting that by f11, diffraction is starting to take the edge off and even at 100% the difference is barely, if at all visible. If you are going to shoot landscapes, with foreground interest, the chances are you are going to be shooting at f11 or so, in which case the difference is immaterial. All the lenses perform a little better on centre at f5.6, for example, but the penalty at the edges is significant. If I have time in the future, I may do a round of testing at these apertures.
As a trend, the Zuikos also have a very slightly higher edge resolution at this distance, but its pretty close in most cases. Again, at 50%, representing a 37” print its not terribly relevant in most cases. You might notice if you went up really close and inspected, but for my money, both sets are putting in a tremendous performance. …. But the Canon FDn lenses have sharper extreme corners. Thse last few mm, right into the corner is better with the FDn lenses in every case. In general, the FDns put in their best overall performance at f8 or f11. At f8 there is fractionally better central resolution, when viewed at 100%, but the last mm or two of the corners are soft. We are talking a tiny weeny part of the frame here, but its there. By f11, the FDns all contain detail right to the tip of corner. The OMs are a stop or so behind i.e at f11, they are about where the FDn lenses are at f8. Now that we have generalisations over, lets look at specific lenses. Please note that now that the CA demo has been shown above, all frames have been subject to LR5 auto removal of CA. Please look at solid structures as the wind did gust periodically and might have affected foliage.
FDn 20 f2.8
As you can see, you are losing a little detail on centre at f11, at 100%, but on my screen you cannot really see a difference when viewed at 50%.
Notice how the resolution is there in the edge/corner at f4! However, there is a dreamy glow to the image.
…. which clears up at f11. This is impressively sharp, when you consider the angle of view and vintage. There is a bit of CA visible even after ticking that all important removal box in LR5; however, this can be removed with some additional manual adjustment, as shown below:
Summary: This is a really excellent lens. Wide open, it shows a lot of spherical aberration and ‘glow’ – the look is definitely ‘dreamy’. By f4 this is gone, on centre, but the edges remain affected. At f8, edges are sharp. By f11, edges are fractionally sharper (the best they get) and sharp into the extreme corners. F11 would be my choice of aperture for landscape use. I have shot this lens in other tests at varying differences and conclude that it is able to fully compete with its less wide siblings. In some cases, it actually has better corners and edge performance. I’d have no hesitation using this lens for serious landscape use. I’m primarily a B&W shooter and I can see 30+” prints with no excuses whatsoever. Where is it best? On the A7, where it delivers superb across the frame performance at f11 and will produce beautiful landscape images. There is no meaningful benefit with the A7R over the regular A7, because it does not resolve highly enough. It does, however, pull out all 24MP from the A7 on centre. The edges are not as sharp, but still very good.
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