During Wolf's early days as an undergraduate and PhD student, he was lucky to be able to study the visual system of barn owls, at the Institute of Physiology II at Aachen University (RWTH), under supervision of Prof. Hermann Wagner. Some of the findings are posted below.
Dare to visit the legacy
Barn owl project pages.

(Beware that links might be broken and some statements outdated.)
Further reading
Legacy website
Harmening WM (2017)
[Contrast sensitivity and visual acuity in animals] Kontrastempfindlichkeit und Sehschärfe bei Tieren.
Harmening WM, Wagner H (2011)
From optics to attention: Visual perception in the barn owl.
Der Ophthalmologe, 114(11): 986-996
[doi:10.1007/s00347-017-0561-4]
Journal of Comparative Physiology A, 197(11): 1031-42
[doi:10.1007/s00359-011-0664-3]
Barn owl vision
Harmening WM, Göbbels K, Wagner H (2007) Vernier acuity in barn owls.
Vision Research, 47(7): 1020-1026 [doi:10.1016/j.visres.2007.01.005]
Harmening WM, Vobig MA, Walter P, Wagner H (2007) Ocular aberrations in barn owl eyes. Vision Research, 47(23): 2934-2942 [doi:10.1016/j.visres.2007.08.001]
Ohayon S, Harmening WM, Wagner H, Rivlin E (2008) Through a barn owl's eyes: interactions between scene content and visual attention. Biological Cybernetics,
98(2): 115-132 [doi:10.1007/s00422-007-0199-4]
Harmening WM, Nikolay P, Orlowski J, Wagner H (2009) Spatial contrast sensitivity and grating acuity of barn owls. Journal of Vision, 9(7): 1-12 [doi:10.1167/9.7.13]
van der Willigen RF*, Harmening WM*, Vossen S, Wagner H (2010) Disparity sensitivity in man and owl: psychophysical evidence for equivalent perception of shape-from-stereo. Journal of Vision, 10(1): 1-11 [doi:10.1167/10.1.10
Harmening WM, Orlowski J, Ben-Shahar O, Wagner H (2011) Overt attention towards oriented objects in free viewing barn owls. Proceedings of the National Academy of Sciences, 108(20): 8461-8466 [doi:10.1073/pnas.1101582108]
Orlowski J, Harmening WM, Wagner H (2012) Night vision in barn owls: visual acuity and contrast sensitivity under dark adaptation. Journal of Vision, 12(4):1-8
[doi:10.1167/12.13.4]