Erwin Puts is well known for his Leica and other photography expertise, and in my exploration of the backfocus issues with my Leica M9, I decided to ask him what his Leica M9 focusing experience had been.
DIGLLOYD: I’ve been having multiple issues with calibration of focus for the M9 and lenses— backfocus in particular. Easy to repeat in the field or a target with various lenses, and that's using the 1.25X magnifier. How has your experience been with focus calibration? Do you take special steps to ensure calibration?
This is a difficult topic. When testing camera/lens combos with the M9 I often need to adjust focus distance to get best contrast and sharpness. The fact that the focus is not always accurate has different causes: the focusing cam on the lens might be out of tolerance or the accuracy of the rangefinder even in combo with 1.25 magnifier is not sufficient.
DIGLLOYD Too bad. I came to the same conclusion, and was hoping you had some "magic". My experience shows that getting perfect focus with more than one or two lenses for the M9 is a serious challenge.
I use two methods' one crude and one systematic. Crude: On a tripod I focus as best as I can, make the picture and enlarge on the display: if sharp OK if not sharp slightly defocus in one direction and if this is sharper continue. If it is not sharper try the other direction.
DIGLLOYD: I have used the same approach, which I deem “LCD zoom focus”. Alas, the M9 does not zoom in to actual pixels, or even sharp pixels, and the low-res screen further degrades the accuracy of that approach. Close, but no cigar. I discuss the whole composition and focus area at length in my review of the M9. I don’t know why Leica can’t offer a once-per-second Live View, it would help. Or a decent LCD screen. Or sharp actual pixel zoom.
Systematic: on a tripod I have a slider mechanism with 1mm distance scale. I focus accurately and have the slider in mid position. Then I take a series of pictures moving the slider in 1cm steps in both directions for a range of 5 cm. On the computer I select the best image.
DIGLLOYD: I sometimes use a slider setup with a 1mm engraving. It works. But it’s useful only for close up work, not at any distance. And of course some lenses don’t perform as well as when focused close, and some also exhibit shift focus when stopping down, so it’s very tedious for each aperture, and not very interesting for real world images.
The back focus issue is a sign that the rangefinder is at its limits. But so are many DSLR cameras. There you can individually calibrate a lens for the AF system.
DIGLLOYD: We are in agreement here in general. Yes, AF isn’t perfect, but it can focus off-center, and in conditions where a rangefinder is hopeless, and it can do so very quickly. Using Live View zoomed in with a loupe eliminates the focus issue for a DSLR entirely. I've rarely had to calibrate lenses for AF, but it’s a great feature. For precision work, Live View is mandatory anyway, as it eliminates a variable. Even contrast-detect AF can be unreliable, with both Nikon and Canon, observed by experience. The reason we don’t see Live View with the Leica M9 or S2 is that CCD sensors do not support it.