Irix 30 mm f/1.4
4. Image resolution
Let’s check how the Irix 30 mm f/1.4 compares; its results in the frame centre and on the edge presents a graph below.
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When it comes to the performance in the centre one word is enough – a sensation. Already at the maximum relative aperture you get a very high result, reaching 42.7 lpmm; on stopping down it only gets better, and by f/4.0 it becomes outstanding with a value of 50.1 ±0.4 lpmm. It's not a new record but such a result places the Irix among a trio of the best lenses tested by us on full frame Canon sensors so far. It is also a value just slightly higher than the result of the very expensive Zeiss Otus 1.4/28.
A graph below presents a comparison between the performance of the tested Irix and two very well-put-together 28 and 35 mm Sigma lenses.
It is clear that the Irix 1.4/30 fares better at practically every aperture but I admit the huge advantage over its rivals by f/11 and f/16 seems to be a bit strange; after such a significant stopping down all lenses should have fared the same. I suppose the result is connected to aperture blades and some innacuracies of closing down. After all, at the 30 mm focal length and the f/16 aperture the hole is less than 2 mm wide; even a fraction of a milimeter can make a lot of difference in terms of resolution values.
The performance of the Irix on the edge of the frame is definitely something you should pay attention to because, for a wide-angle lens, it is simply outstanding. It's enough to say it differs just slightly from the performance in the centre of the field.
On the edge of the APS-C/DX sensor and at the maximum relative aperture you deal with a very good resolution level of over 37 lpmm; the maximum values are once again outstanding, by f/4.0 and f/5.6 amounting to a tad higher than 43 lpmm. Also the edge of full frame doesn't show even traces of any weaknesses. By f/1.4 the results exceed 35 lpmm; it means images are of at least good quality. In the aperture range from f/4.0 to f/8.0 the lens is able to exceed an excellent level of 40 lpmm.
I don't doubt that the Irix constructors profited from the fact that they hadn't been restrained by any weight and/or size limitations – because of that they constructed a lens with simply outstanding resolution.
At the end of this part of our test, traditionally we present crops taken from photos of our resolution testing chart saved as JPEG files.
| Canon 5D MkIII, JPEG, 30 mm, f/1.4 |
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| Canon 5D MkIII, JPEG, 30 mm, f/4.0 |
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