X100 lens performance oddity

[Turtle]

With absolutely nothing better to do, I shot a number of frames out of my back door (towards a fence with trees directly behind) starting at F2, until F11, to see how the lens performed and whether there were any glaring concerns where diffraction hit hard etc.

It was odd to note that the edges got sharper from F2 to 2.8, but actually got worse at F4-5.6 (from f2.8) then jumped up in performance again at F8, 11 etc. This is most peculiar. The difference is not huge, but plainly visible.

from f2-2.8 there is an obvious leap in contrast as well, but by f4 it does not seem to increase much. Resolution on centre remains unchanged from F2.8 until about f8, after which diffration sets in.

How on earth can a lens get sharper on the edge one stop down, get worse for next two f stops, then leap up again at f8. I have repeated this numerous times and it is plain as day and not my imagination!

[Moriturii]

Curvature of field? Just a guessing, I don't know.

[kbg32]

People have too much time on their hands. Just enjoy the camera. In practical usage, you probably won't notice anything. If you do, time to sell it and get something else.

[jsrockit]

Every lens has an optimum f stop... a few have said that f/4 is the optimum on the X100. I don't worry about crap like this... it is good at every normal f stop as far as I'm concerned.

[Turtle]

Calm down people. Its interesting to note that two out of three have passed some sort of instant judgment about the 'problem' I have for noticing this.

I am just curious as to how this happens. Lens curvature sounds about right with improvement from 2-28, optimum at 2.8 and passing the point of flatness until DOF catches up with curvature at F8.

I didn't say it mattered, I have just never seen this before with a lens.

[Kavenzmann]

I havent't tested mine the way you did, but it also seems curious
for me the the camera/lens performs that way you describe here.

Maybe your lens has the "sticky aperture problem" or did you do the
test fully manually?
Mine was fixes after I recognized the problem the 2nd day I owned
it. Since Fuji fixed it, the X100 follows wherever I wanna take a
camera with me and so far I understood the lens performance as
a little soft in the edges at f2, better at f2,8 and perfect from f4 to f8.
But I never checked that with mine.
When I find some time the next weeks I'll check that,

Kavenzmann

[gavinlg]

I've never checked mine out critically, and to be honest, I'm not going to. Mine is very good at f2, excellent at f2.8, and near perfect f4+. It is a rather quirky little lens though, so I don't doubt the characteristics you describe. When it comes to flare and color in backlight it has some very peculiar (though not always displeasing) characteristics...

Great lens though regardless.