David Farkas;420 wrote: In the world of Canon or Nikon, a faster aperture lens is almost always universally a better lens than a slower lens in the same focal length. The fast lenses are the “pro” lenses and the slower lenses are the “entry-level” or “consumer” lenses.
This distinction between ‘pro’ and ‘consumer’ lines of lenses emerged together with the advent of autofocus systems. Before that, in the ’60s, ’70s, and early ’80s, lens manufacturers produced their slow lenses to exactly the same optical, mechanical, and manufacturing standards as the faster ones. A slower lens was just slower, but not worse in any way. This changed in the ’80s and apparently keeps becoming worse every year. If you want a good lens then you have to get the fastest, even when you don’t want the bulk or weight associated. Leica (and I guess Zeiss, too) is one of the few companies who didn’t adopt this two-class lens manufacturing.
David Farkas;420 wrote: As I tell people who are new to Leica, there are no bad Leica lenses.
Exactly. Still, the Summarit-M line has a poor reputation. I guess mostly it’s due to the pro-vs-consumer dualism found elsewhere. The fact that the Summarits look different than Elmarits, Summicrons, or Summiluxes reinforces the impression of apparently being inferior … and Ken Rockwell’s lunacies aren’t helpful, either. :rolleyes:
David Farkas;420 wrote: I’m intrigued by your findings that the 50 Summarit offers more DOF than the 50 Lux ASPH at equivalent apertures. Optical physics should dictate that the DOF would be the same on any 50mm lens on the same camera. Looks like Josh and I have some testing to do on Monday.
You may start your research with Leica’s own tech specs which you can find on their homepage. There’s a PDF document for each lens for download, and these include depth-of-field tables. There you can see that indeed the Summarit-M 50 mm has more DOF than, say, the Summilux-M 50 mm Asph. In actual pictures, the difference in DOF is hard to see—but along with wider DOF comes less background blur, and that is pretty obvious. Also note the varying character of the out-of-focus rendition in the foreground, in the near background, and in the far background at various apertures.
One—widely unknown—factor that affects DOF, besides aperture, focal length, distance, and image format, is pupil magnification. All other parameters being equal, greater pupil magnification means less DOF. However the effect on DOF is significant only at (very) close range. At normal (non-close-up) distances it’s insignificant, and at or near infinity the effect is virtually zero. So pupil magnification cannot explain the Summarit’s DOF difference. After all, there is hardly any difference in pupil magnification berween Summilux and Summarit to begin with … but as I said, there seems to be a difference in entry and exit pupil sizes, which is strange.
By the way, a similar difference in DOF and background blur also can be found in the pair of Summilux-M 35 mm Asph and Summarit-M 35 mm, albeit to a lesser degree than in the 50 mm lenses. My hypothesis is, the aspherical design somehow amplifies the difference between in-focus and out-of-focus … but that’s just a speculation of mine, taken out of thin air.
David Farkas;420 wrote: Also, interesting that you prefer the 75 APO. It is a stellar lens, no doubt. The 75 APO and 50 Lux ASPH are essentially the same optical design with the 75 dropping one element due to slower aperture requirement and slightly longer focal length.
Yes, I am aware of that. And if you look at the MTF diagrams in Leica’s tech specs then you’ll see the the Summilux-M 50 mm Asph’s curves, high as they are, take a drop in the farthest corners (even at f/5.6) while the Apo-Summicron-M 75 Asph’s don’t—the later has an uncannily high level of performance across the whole field including the farthest corners, even at full aperture. And it shows in the pictures … umm, sometimes. Still, the main reason why I often prefer the 75 over the 50 is not corner sharpness but the fact that I simply prefer a slightly narrower field-of-view. Most rangefinder users prefer 35 or 50 mm as their ‘center of gravity’ of lens choices—for me it happens to be 75 mm.