据说这是好镜头的表现, quoted from ll: Those "tiny black specks" are what you get when the lens is an odd number of half-wavelengths out of focus. Note how both the foreground and background point sources gradually show an increasing pattern of light and dark rings - and more critically, how these ring patterns exhibit identical shapes and intensities at a given degree of defocus in front of and behind the plane of sharp focus? That beautiful symmetry, between inside and outside focus, is a sign of near-perfect optics! Diffraction spikes from the aperture blades are causing a certain jaggedness of the diffraction rings, but that's to be expected with a non- circular aperture. The image is also over-sharpened, for my taste, which increases the contrast between the bright and dark regions of the diffraction pattern at small degrees of defocus. I don't know what lens this is, but at this f-stop and object distance, its spherical correction looks good to at least 1/6 wavelength . The Rayleigh criterion only calls for 1/4 wave accuracy for an optic to earn the label "diffraction limited". http://www.luminous-landscape.com/forum/index.php?topic=46162.80
g*d
42 楼
无知的九零后问一句怎么看焦外的好坏啊?
o*x
43 楼
我觉得这两种情况不太一样吧。
【在 f**********c 的大作中提到】 : 据说这是好镜头的表现, quoted from ll: : Those "tiny black specks" are what you get when the lens is an odd number : of half-wavelengths out of focus. Note how both the foreground and : background point sources gradually show an increasing pattern of light and : dark rings - and more critically, how these ring patterns exhibit : identical shapes and intensities at a given degree of defocus in front of : and behind the plane of sharp focus? That beautiful symmetry, between : inside and outside focus, is a sign of near-perfect optics! : Diffraction spikes from the aperture blades are causing a certain : jaggedness of the diffraction rings, but that's to be expected with a non-