Olympus M.Zuiko Digital ED 12-45 mm f/4.0 PRO
4. Image resolution
Now let’s check how the tested lens compares; a graph below presents its results in the frame centre at 12, 25, and 45 mm.
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While testing resolution of f/4.0-5.6 Micro 4/3 system lenses I always wonder how difficult the task of optics constructors really is. With such values of relative apertures difraction becomes already an important factor. For the same reason resolution records and, generally, the highest results in this system are usually registered near the f/2.8 aperture.
If a lens's maximum relative aperture amounts to f/4.0 it faces a very difficult task in this category. There's simply no room for mistakes that might lower MTFs in the 1-2 EV range from the maximum relative aperture because on stopping down there is no further room for improvement available. By f/8.0, so on stopping down the aperture by 2 EV in order to limit optical aberrations, available MTFs reach 70 lpmm so are much lower than the record value of almost 100 lpmm.
It seems Olympus optics specialists have to do their best in order to correct the lens already by f/4.0 and f/5.6 apertures. Looking at the graph above we are pleased to say they managed to do it perfectly well. The values are simply excellent for an f/4.0 zoom lens. It seems that already by f/5.6 – and we mean here all focal lengths available – the lens works in its difraction limit and the influence of optical aberrations is reduced to the minimum. What's more, at the maximum relative aperture the results are even better and, as a result, the MTFs keep an excellent level of 80-90 lpmm. A really impressive performance!
Now let's check the situation on the edge of the frame – an appropriate graph you can find below.
For obvious reasons the lens didn't repeat its frame centre miracle performance so the peak is reached not by f/4.0 but by f/5.6. Still we wish all zoom lenses, tested by us, on the edge of the frame reached such sensible maximum results already on stopping down the lens by 1 EV. After all results close to 70 lpmm on such a sensor should be considered a very good level and they deserve to be praised. What's more, values reached at the maximum relative aperture are hardly weaker - 60-70 lpmm mean the lens's resolution is very distinctly above our decency level so the instrument can produce quite satisfying, good quality images.
I can say that the Olympus M.Zuiko Digital ED 12–45 mm f/4.0 PRO surprised me very nicely in this category. To be honest I doubted whether such high results could be reached already from f/4.0 and f/5.6 apertures. Constructors of this lens proved me wrong and I am very happy with such a positive surprise.
At the end of this chapter, traditionally, we present crops taken from photos of our resolution testing charts; these were saved as JPEG files along RAW files we used for the analysis above.
| Olympus E-M5 II, JPEG, 25 mm f/4.0 |
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| Olympus E-M5 II, JPEG, 45 mm, f/4.0 |
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