Resolution and Wishful Thinking...

I've been on conversations with fellow engineering colleagues where, over the years, we tend to note just how disconnected from reality some people are who make claims about resolution and it's effect on photographic image making. Typically, arguments arise in on-line forums where someone will claim that Zeiss lenses are "the best" and someone else says Leica "can't be beaten", and all parties claiming they can tell the difference in images made with different lenses. DP Review is pretty typical of this effect.

The claim that really takes the cake is the one Zeiss and other manufacturers use when they say a lens "writes" well. What the hell is that? Optics are optics and physics is still physics. It's all bunk. There's no truth to those kinds of claims, no matter what some folk would like to believe.

In optics, lens design, when well-executed in manufacturing, tends to not be the limiting factor in resolution. It's either the film or the sensor (depending on which technology you use).

The following is a chart of theoretic limits of resolution of a perfect lens at various apertures.

Resolving Power

This presents the theoretic resolving power of an ideal lens where the light's
wavelength is 589.3mu (green).

Tangential lines/mm
f-number Angular distance from axis (in degrees)
    0    10    25
1     1391 1329  1035
2     695  665   518
4     348  332   259
5.6   246  235   183
8     174  166   130
11    123  117   92  <--- approx. limits of film/sensor resolution
16    87   83    65
22    61   59    46
32    43   41    32
45    31   29    23
64    22   21    16

Radial lines/mm
f-number Angular distance from axis (in degrees)
    0    10    25
1     1391 1370  1260
2     695  685   630
4     348  343   315
5.6   246  243   223
8     174  171   158
11    123  121   111  <--- approx. limits of film/sensor resolution

16    87   86    79
22    61   61    56
32    43   43    39
45    31   30    28
64    22   21    20

Which means that diffraction limits really can't come into play in any meaningful manner until a lens is stopped way down to at least f/11. Even then, most modern digital sensors are resolution limited to around 70 lp/mm. So with those systems (such as with either Canon's, Nikon's, or Sony's full frame sensor'd wonder boxes), diffraction in the pure optical physical sense will not come into play until you're well beyond the limits of what a lens offers. ie: f/16

As sensor resolution rises, diffraction will still not come into play as many photographer shoot at apertures brighter than f/11.

Said another way, I've never met a lens I didn't like. Some, yes, I liked more than others. But seldom, if ever, were the issues of "liking" a lens related to it's ability to be sharp.

I've shot them all. Leica. Zeiss (small, medium, and large formats). Canon. Nikon. Pentax. Mamiya (medium format), Schneider (medium format, large format). Sigma (I know people claim to hate these lenses, but I can't find fault with them, they're wonderful optics, regardless of money). Dagor (large format). Kodak (small, medium, large formats - brilliant optics from WWII until the mid-1960's).

It's not a matter of the lens. It's the nut behind the eyepiece.

So there. Now go out and make some fine images. Forget about the blather on those forums. OK?