Center not sharp as apearture increase on 100mm macro?

Hi,

I just got myself a EF100mm f2.8 macro lens. This is the 1st time I own a macro lens. Did some test shots at home with tripod mount, cable release and mirror lock up. The following are the results as I increase the apearture from f5.6 to f8, f11, f16, f22, f29 and f32.

1. The center getting sharper as i inrease the apeature from f5.6, f8, f11 and f16, After f16, the center sharpness amd contrast start to drop.

2. At the corner, the shaprness and contrast increase as I increase the apearture from f5.6 all the way to f29.

Is this the normal? Is this the characteristic of a maco lens? It's seems like the peak performance of this lens is at f11 to f16.

its called Diffraction softening.
happens to every single lens
happens with narrow apertures

edit; here's a great thread to show whats happening.
https://photography-on-the.net/forum/showthre​ad.php?t=209960

Red Dot wrote in post #5541465
its called Diffraction softening.
happens to every single lens
happens with narrow apertures

edit; here's a great thread to show whats happening.
https://photography-on-the.net/forum/showthre​ad.php?t=209960

Hi Red Dot, thanks for the info. Does the optimum apearture of a lens depends on the distance of the subject as well?

Look at the MTF chart for this lens at Photozone.de and you'll see what difference it makes to use different apertures. Distance doesn't really factor into this.

vinwin wrote in post #5543177
Hi Red Dot, thanks for the info. Does the optimum apearture of a lens depends on the distance of the subject as well?

It can, depending on the lens. Not so for the 100 macro, or most macros allowing infinity focus, however.

What is important is sensor size. Diffraction starts biting around F/13 for APS-C cameras, and at about F/18 for FF cameras. This also depends a bit on the lenses used, but you can take this as a general guideline.

Kind regards, Wim

wimg wrote in post #5543973
It can, depending on the lens. Not so for the 100 macro, or most macros allowing infinity focus, however.

What is important is sensor size. Diffraction starts biting around F/13 for APS-C cameras, and at about F/18 for FF cameras. This also depends a bit on the lenses used, but you can take this as a general guideline.

Kind regards, Wim

Nice info. I didn't know sensor size was a factor in diffraction.

Hi Ed,

silvex wrote in post #5554116
Nice info. I didn't know sensor size was a factor in diffraction.

Yes, which again is caused by the CoC. Since a smaller sensor has a smaller CoC, diffraction cuts in sooner.

Kind regards, Wim

silvex wrote in post #5554116
Nice info. I didn't know sensor size was a factor in diffraction.

its not really a disadvantage to full frame though.
you get more DOF with a smaller sensor therfore you dont need to stop down as much and therfore about equal diffraction to a full frame body.

Red Dot wrote in post #5557117
its not really a disadvantage to full frame though.
you get more DOF with a smaller sensor therfore you dont need to stop down as much and therfore about equal diffraction to a full frame body.

At the same level of DoF for the same FoV, more or less, yes. It is about 1/3 stop less diffraction in that case with FF .

Kind regards, Wim