Leica M Typ 240: Part 3 (pixels)

Above: 35mm Summilux ASPH (non-FLE), wide-open
***Note: click on pictures to enlarge

You’re going to lose your religious beliefs. There is a lot of talk about “rendering” and something special with the M9 and its CCD. When these people use an M long enough (and it does not take that long), they will wonder why they tolerated the Atari-age eletronics or the low-light performance (or lack thereof).

Challenges to image quality

The fact is that the Leica M’s 24mp is verging on the usable resolution of a 6×4.5 negative at ISO 400 and above. With no antialiasing filter and a new pixel well solution, it actually presents fairly stunning results. The catch, sadly is that three things hold back the camera.

a. Limits in the lenses.  One limitation is older lenses (i.e., those before the late 1990s). Though charming in contrast and focus characteristics, they resolve less than the sensor can. And where they have uncorrected spherical aberration, they exhibit very obvious focus shift. This makes the extra resolution over the M9 (15% linear in each dimension) seem a fairly marginal proposition. The concept that comes to mind, though not completely apposite, is empty magnification in microscopy. You can multiply the pixels as much as you want – but in the end, the lens is not delivering enough information to make use of them. This is part of the problem with the D800E (and soon-to-be Sony A7r)

b. The human factor. The other problem is poor technique. With high pixel density, errors like poor focusing and camera shake are more apparent. Lenses of 90mm and up are difficult to use with the M’s rangefinder. They are already challenged because they are in the range where an SLR (or an EVF) does better with focusing. But the killer is camera shake. A good rule of thumb with the M is to set a shutter speed that is at least double the reciprocal of the lens length.  A low-speed threshold of 1/125 second for Auto ISO is advisable.

c. Moiré. The new system uses considerably less aggressive moiré removal than the M8 and M9. As a result, the smallest resolvable details in shots (like the texture of bricks, for example) may pick up a little moiré sparkle. This is the downside of the clamoring to eliminate antialiasing filters.

 

Downsampling

The thing about having a very high resolution sensor is that it allows you to throw away data to get a better result. And it is fairly well documented that a large image downsampled to a smaller size is typically better than a small image that started that size. This is why you lose nothing with old lenses when going to 24mp. It also enables pretty spectacular high-ISO peformance.

High-ISO performance

The short of it is that the M crushes the M8 and M9 in high-ISO performance. There is plenty of quantification available on the interwebs, but here are the key things I have noted are:

• High-ISO (≤2500) is almost exactly the same as the D700 – except that you have twice as many pixels in play.
• ISO 3200 is completely usable, but dynamic range starts taking a beating. At a pixel level, it is still comparable to a Fuji X-Pro 1.
• ISO 6400 has regular pattern noise but is no worse than Tri-X pan film in b/w; no worse than scanned 400 color film.

If you want some concrete information on the last point, here is an example from where I accidentally shot a picture in broad daylight at ISO 6400 with an SF-58 flash. It’s a small miracle this worked at all, but here is the Tri-X detail at 4 stops more sensitive (and this is straight out of LR, with no attempt to fix the noise):

As with all other cameras, the lower the color temperature (i.e., incandescent light), the more noisy high ISOs become. This is due in part to the fact that auto white balance is trying to raise a blue channel that is at the noise limit.

Auto ISO weirdness

The fact that Auto-ISO doesn’t work for manual shutter speeds is well documented. As is the fact that your choices are either to go with the reciprocal of the focal length (if a lens is coded or selected) or an arbitrary shutter speed limit.  One wrinkle that is not documented is what happens with flash.  When the flash (whether Leica or Nikon-style) tells the camera it is ready, the ISO changes to the last value set in manual mode. To get to the picture above, I had previously used the 6400 speed to shoot at night. Taking a fill-flash shot during the day caused the ISO to change from auto to 6400. If you plan to use fill, I would recommend taking a couple of shots at ISO 800 in manual shutter speed mode to use that speed.

As against the M8/M9

The M is thoroughly modern in its sensor performance, whether measured as a function of resolving power or low-light performance. The move to CMOS, though lamented by the hard core of M9 users, has produced no measurable change in “rendering” and has increased low-light performance at least a couple of stops (and the collateral effect is to allow video). Not bad.

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