MarcoS said:
I briefly read the italian article and indeed there are a couple of images that show banding.
The reviewer (Roberto Piero Ottavi) stated that the banding occured only with his Voigtlander 28 Ultron and it doesn't show when using any Leica lens (either asph or pre-asph) maybe because of "compatibility issue" between microlenses and light angle from non-Leica lenses.
But you can easily see the vertical (actually horizontal giving the portrait orientation) banding in the Noctilux image, so maybe we have a real issue here.
Yes, I can see it too. It's not as evident in the Noctilux image because the bright streak (from the small street lamp in the background) lines up fairly closely with a light area in the background. Against a completely black background I suspect it would be more visible.
It's too late and I've got too busy a weekend coming up to do this myself, but here's a suggested test rig for someone who'd like to explore this phenomenon:
-- Get a large sheet of some black, opaque material such as black foamcore board. Given the typical RF lens minimum focusing distance of 1m, you'll probably need a sheet about 0.5m high; the US standard 20x30" sheet should be about big enough.
-- Cut a thin, vertical slot in the center of the sheet, tall enough to occcupy about 1/4 the frame height.
-- Set up the sheet vertically in front of your digital camera, focus on the slot, and then backlight the slot from behind with a very bright light source such as a quartz lamp. Make sure there's no spill around the sheet.
-- Take test shots at various apertures and with the slot at various positions in the frame. This should enable you to determine such things as:
1) Do streaks appear? If so, what amount of overexposure does it take to provoke them?
2) If you get streaks, do they expand uniformly (blooming) or do they run in one specific direction? (The examples I've seen run in a specific direction; I suspect this is because the data is scanned horizontally off the imager.)
3) Is the streaking independent of shutter speed, or not? (I'm guessing it is, since the electronic scan of the imager is much faster than the mechanical shutter curtain's travel.)
4) Is the streaking constant across the field, or does it fade out toward the far edge? (I'd think it would fade out as the excess signal dissipates, but it's difficult to tell on the examples I've got because the backgrounds aren't uniform.)
5) Is the effect independent of ISO setting, or not? (I don't know, but
maybe higher ISOs are more likely to streak since this involves greater amplification of the analog signal off the imager. If using a lower ISO definitely reduces the risk of streaks, this would be useful knowledge!)
6) Do different lenses have any effect? (If it's purely an imager phenomenon, they shouldn't -- but lens flares might be mistaken for this type of streaking.)
7) If you've got several different types of digital camera available, comparing them would be an interesting exercise.
You film diehards, with your symmetrical, streak-free, aesthetically pleasing overexposure effects, have my permission to smirk smugly at this point...
