Originally posted by RobA_Oz Kodachrome's resolution was said to be around 20MP equivalent. Obviously, film grains aren't as neatly arrayed as a sensor's elements, but the K-3's sensor clearly exceeds that figure, and the Nikon D810 does so by a wide margin.
Strangely, that is not the case regarding the digital sensors. Translation of MTF data to lp/mm yields values of about 170 lp/mm for today's best lenses on a 36Mpx FF sensor. Current TMax 100 film attain base resolution of about 150 lp/mm and Mahn in Germany claims 300 lp/mm for their ATP 1.1 product. The late and much lamented Kodak Technical Pan was capable of 200 lp/mm. I threw those numbers in not for comparison, but to indicate that film resolution is of the same order of magnitude as current sensor technology.
As for the 20 Mpx estimate for scanned Kodachrome, that is an Internet legend based on the pixel count for a 24x36 slide scanned at 4000 dpi. A 4000 dpi scan of drug store film yields the same 20 Mpx. Optical resolution is measured in lp/mm not megapixels. The resolution of Kodachrome was tested by Modern Photography in 1978. Kodachrome II's best result was measured at 86 lp/mm when paired with the Leitz Summicron 50/2. The last product insert for Kodachrome 64 includes a MTF graph of base resolution (no lens) indicating similar performance for that product as for KII. Apparently the resolution of Kodachrome was the limiting factor the tested lenses in 1978. Contrary to conventional wisdom, Kodachrome was never the paragon of film resolution and no lens was designed around it as a performance target. Failure to perform on Kodachrome was inexcusable in a professional grade lens and in many ways it was the lowest indicator of acceptable performance, but most monochrome films did and still do present a stiffer optical challenge.
I have oversimplified the film resolution story as well as the challenge of extracting maximum resolution from a film + lens combination, but the truth is that most film era lenses perform quite well on modern digital sensors and also on modern high resolution films. The "designed for film and therefore lacking" argument is patently invalid. So is the talk about sensel density as a point of comparison. Yes, there is a tendency to oversimplify the digital resolution story as well.
Back to a lens being out-resolved by a sensor. There are good lenses and there are crummy lenses. Having a competent sensor or an incredibly good technical film does not make a good lens worse. Neither does a crummy sensor or nasty film even the playing field between lenses.
As noted above, a great sensor allows most decent lenses to attain their best performance and nothing more. A decent analogy would be a race car. The optics are analogous to the engine, drive chain, and suspension. The sensor/film is analogous to the tires.** Crummy tires and you can't go fast regardless of the excellence of car and driver. Excellent tires and your speed is determined by engineering and driver skill.
Steve
(...still shoots film and has scanned a ton of Kodachrome as well as the better B&W films currently available...currently shoots the same lenses on both film and the K-3...gets similar results from both, at least for monochrome...color films are not so good...
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* Traditional film resolution testing is done using a microscope to evaluate the target image on the slide/negative. There are only the lines from the target, no pixels or image processor. More recently it is done using digital processors to generate MTF graphs similar to those used in lens tests.
** Yes, despite the current techie obsession over sensors they truly are the minor part of the puzzle...critical , but minor. The biggest challenge in digital photography is to provide sensors that are truly up to the capability of available lenses.