10-25-2016, 05:47 AM
The problem with the sharpest apertures is how the effective aperture changes with the distance:
I used to have the Sigma 105mm macro non OS version shooting on the Pentax K3. (sold,can't give figures)
But looking at the Nikor AF 55mm F2.8 macro, aperture changes with distance are:
Infinity...F2.8 0.35 mts...F3.5 0.27 mts....F4 0.24 mts... F4.5 0.23 mts ...F5 at 1:1...F5.5. nearly minus 2 stops.
And for the Sigma 150mm EX F2.8 non OS version.
Infinity...F2.8 3.0 mts. F3.5 0.8 mts...F3.8 0.58 mts...F4 0.5 mts...F4.5 at 1:1 .. F5.6....minus 2 stops.
So finding which aperture is the sharpest will vary according to the distance. resolution tests would have to be done at a range of distances at all apertures, not something I will pursue!
In practice when not "focus stacking" we compromise to have a visually pleasing depth of field, often F11, which is way beyond the lens's optimum sharpness which is commonly F4.5-5.6.
I used to have the Sigma 105mm macro non OS version shooting on the Pentax K3. (sold,can't give figures)
But looking at the Nikor AF 55mm F2.8 macro, aperture changes with distance are:
Infinity...F2.8 0.35 mts...F3.5 0.27 mts....F4 0.24 mts... F4.5 0.23 mts ...F5 at 1:1...F5.5. nearly minus 2 stops.
And for the Sigma 150mm EX F2.8 non OS version.
Infinity...F2.8 3.0 mts. F3.5 0.8 mts...F3.8 0.58 mts...F4 0.5 mts...F4.5 at 1:1 .. F5.6....minus 2 stops.
So finding which aperture is the sharpest will vary according to the distance. resolution tests would have to be done at a range of distances at all apertures, not something I will pursue!
In practice when not "focus stacking" we compromise to have a visually pleasing depth of field, often F11, which is way beyond the lens's optimum sharpness which is commonly F4.5-5.6.