Originally posted by stevebrot PF member Nesster has a Modern Photography article from the mid-1980s on his Flickr photostream where attempts were made to extract 100 lp/mm from lenses (all fast-50s) and films available at that time. IIRC, that number proved illusive. I will see if I can find it and post it here if I do.
I found it! Reading from a larger copy at Flickr is easier, so click through on the link and/or the full resolution link I am providing.
Higher Resolution versions of "How Sharp Can You Get?", p1 Higher Resolution versions of "How Sharp Can You Get?" - continued
The entire article, despite dating to the early 1980s, is pertinent to the technical aspects of this discussion as well as to best-case user expectations. Of particular interest is methodology for determining captured resolution. Note that from a selection of available lenses from the major vendors, the Pentax-M 50/1.7 made the cut over faster offerings. The same was true across the board with nothing faster than f/1.7 in the test. Here are a few of the highlights:
- The only color film to deliver 100 l/mm was Micro-Ektachrome
- No emulsion intended for general pictoral photography was able to deliver 100 l/mm with any of the lenses surveyed
- No the Pentax 50/1.7 did not sweep the field; that honor went to the Leitz Summicron 50/2
- No, dedicated macro lenses did not outperform any of the fast 50s, even for close focus
- Focus bracketing was required for all lens/camera combinations
My favorite paragraph runs as follows:
Quote: To understand why we could not readily get 100 lines per mm using Panatomic-X film, we looked at the MTF (Modulation Transfer Function) curves available from Eastman Kodak for their films. These MTF curves gave us an idea of how good the lens would have to be in terms of image sharpness to yield 100 lines per mm on film. Panatomic-X film exhibits a modulation (contrast) of about 40 percent at 100 lines per mm. If we assume that we need at least 20 percent contrast to barely resolve two lines close together on the film, the image formed by the lens has to deliver at least 50 percent contrast at 100 lines per mm. Well, this sounds easy. However, if the lens is operating at f/5.6, then the theoretical limit of resolving power is around 320 lines per mm. And even if the lens is perfect, the contrast at 100 lines per mm is only about 60 percent. The slightest error in focusing quickly reduces this 100-lines-per-mm contrast to below 50 percent even with the perfect lens. From the results we obtained, it appears that most of the lenses we tested came pretty close to optical perfection at f/4 or f/5.6. But since we are working so close to the theoretical limits imposed by MTF and resolution, reaching 100 lines per mm on film is quite difficult. (emphasis mine...SB)
But wait! There's more!
As noted above, the Summicron 50/2 performed the best in the testing. That same lens (1979 version) has been tested at what used to be photozone{.}de (now opticallimits{.}com) on the Leica M9 (18Mpx FF). The center resolution results...
f/2.8 -- 3096 lw/ph (129 l/mm)
f/4 -- 3265 lw/ph (136 l/mm)
f/5.6 -- 3228 lw/ph (135 l/mm)
The Summicron 50/2 did somewhat better with an 18 Mpx sensor than on 35mm film despite observed focus shift on stop-down. I could not find whether their test method includes focus bracketing.
Now, the bad news...
Nikkor AF-S 50/1.8 G on the 24 Mpx D3x @ f/5.6 -- 3958 lw/ph (165 l/mm)
Canon EF 50/1.8 STM on the 21 Mpx 5DII @ f/5.6 -- 3742 lw/ph (156 l/mm)
Ummm...the Summicron is running a bit behind a couple of recent consumer grade lenses. Granted, both were run against somewhat higher resolution sensors, but still those numbers are sobering.
But...but...but...Those differences in sensor pixel count are important. Consider the
theoretical maximum for each:
Leica M9 -- 3472 lw/ph (145 l/mm)
Nikon D3x -- 4032 lw/ph (168 l/mm)
Canon 5DII -- 3744 lw/ph (156 l/mm)
Normalizing to percentage of theoretical maximum, it is quite likely that all three lenses are sensor-limited on the test cameras.
Conclusion?
The value proposition for moderate focal length primes has never been better. For example, the Canon EF 50/1.8 STM also outperformed the Sigma 50/1.4 DG HSM (Art). In addition, while evidence is hard to come by, the rare objective test and numerous example images tend to indicate that many older lenses continue to perform at or near the theoretical limits for the sensors they are paired with.
With zooms, it is somewhat more difficult to make similar claims. Objective tests for zooms released more than about 15 years ago are hard to come by. What's more, it is pretty much established dogma that all but the newest zooms are troublesome junk and not worth shooting with. I would tend to agree except that I have done some decent work recently with the Pentax-A 70-210/4 on the K-3...go figure
Steve