In my latest post I showed us pictures of night landscapes made with my fish-eye lens (a Samyang 8 mm f/3.5 Aspherical IF MC Fish-eye). In night photography, the hyperfocal distance is a mandatory element and short focal distances are good too, so I've decided test the sharpness of my fish-eye for all apertures, focusing to hyperfocal distance (or larger). In these conditions, every object placed between the half of the hyperfocal distance and the infinity must be showed sharp. The hearth was placed at that range.
I'm sorry because while the pictures were taken the light conditions changed. You can click in the images to view them larger.
What picture is sharpest? It's a difficult question. I think the best photos of this series were taken with apertures f/9.5 or f/11, in the middle of the range. The aperture's extreme values don't seem be very good: the sharpness at f/3.6 or at f/22 (minimum and maximum values) is not very good. It seems increase between f/5.6 and f/11.
Now I show the approximate values that I used in this photos:
The minimum focus distance for this lens is 30 cm (maybe 29 cm), so I couldn't down the focus distance under that value. The hearth was placed at approximate 2 m of distance.
The changes in the light and the focus ring's precision could produce some errors in this little experiment, so you mustn't take it seriously enough. For a much more professionally analysis, check LensTip.com.
Lenstip.com thinks the best aperture for sharp photos with this lens is f/5.6 for objects in the centre of the frame and f/8 for objects in the edge of the frame (my test is for objects in the centre of the frame). As I've written before: Don't take me seriously enough :p! The conclusion is: apertures values between f/5.6 and f/11 produce not bad enough results.