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Lens review

Irix 15 mm f/2.4 Blackstone

27 September 2016
Szymon Starczewski

7. Coma, astigmatism and bokeh

The coma cannot be spotted at all on the APS-C/DX sensor but if you progress to corners of full frame there are visible deformation of images of the diode. The performance seems to be a bit worse than that of the Samyang 14 mm f/2.8 ED AS IF UMC.

Center, f/2.5 Corner APS-C, f/2.5 Corner FF, f/2.5
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh
Center, f/3.5 Corner APS-C, f/3.5 Corner FF, f/3.5
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh


Night sky shows a similar situation. Once again on edges of full frame you can notice distinct deformation of images of stars and they are shaped exactly like the diode presented earlier.

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Canon 5D Mk III, JPEG, f/2.5, upper right corner of the frame 1:1
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh


The astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to just 3.1% so shouldn’t be very bothersome. The official result of the Samyang 2.8/14 was even lower but both these values are alike within the margin of error and both remain practically imperceptible.

The blurry out-of-focus areas are quite nice for a lens with such parameters. Defocused circles of light don’t have any worrying features: the light spread is even, without any distinct rims or local extremes.

Center, f/2.5 Corner APS-C, f/2.5 Corner FF, f/2.5
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh
Center, f/3.5 Corner APS-C, f/3.5 Corner FF, f/3.5
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh
Center, f/5.0 Corner APS-C, f/5.0 Corner FF, f/5.0
Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh Irix 15 mm f/2.4 Blackstone - Coma, astigmatism and bokeh