Lens review

Irix 30 mm f/1.4

16 March 2022
Maciej Lata³³o

4. Image resolution

The resolution test (resolution meaning MTF50 function) of the Irix 30 mm f/1.4 was based on RAW files from the Canon EOS 5D Mark III. In the case of that reflex camera the decency level is situated near 30-32 lpmm and high quality, top-of-the-range fixed focal length lenses can reach a maximum level of 45-50 lpmm . The resolution record on that sensor belongs to the Sigma A 135 mm f/1.8 DG HSM and it currently amounts to 51.6 lpmm .

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.

Irix 30 mm f/1.4 - Image resolution

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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.

Irix 30 mm f/1.4 - Image resolution

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
Irix 30 mm f/1.4 - Image resolution
Canon 5D MkIII, JPEG, 30 mm, f/4.0
Irix 30 mm f/1.4 - Image resolution