I happened to see the latest Popular Photography issue at the store today. I've never given much thought to the magazine since the first time I look at it during the days of film and laughed at their conclusions.
In the current issue, they were reviewing the Panasonic DMC-GH3, a camera body I recently bought. They had a bar graph for noise at each ISO sensitivity setting. First, they had ISO 100, which isn't a setting in the GH3. I guess they couldn't be bothered to put the actual number in their graph, although in the same area of the review, they had ISO 125.
Concerning noise, they had ISO 1600 and up as unacceptable. I'm not sure how they can tell what is acceptable or not. When I worked with film, ASA(ISO for digital) 400 film was usually acceptable, especially with the later formulations, and it is horribly worse than most digital sensors of the past few years. Whether it's the grain of black and white, incorrect pigment of color, or digital noise, who can say definitively what is acceptable?
Other reviews have said that at ISO 800 on the GH3 (and I believe, the Olympus E-M5), noise is creeping into the photos. That makes sense since that number was where the problem really started with the E-1. My own experience tells me that the images I'm getting at ISO 1600 are very clean and the images at ISO 3200 are reasonable, but not beautiful. After that, don't expect much of anything positive. Yes, I've seen people claim to get really good photos at 12,800 but I don't believe it's likely unless they're working with a Nikon D4.
Still, for someone to put a wall up saying "unacceptable" seems unacceptable in itself. It's difficult to quantify and impossible to generalize that all photos fit into one category. I would agree that a photo is likely to be more noisy at a certain ISO sensitivity but to be unacceptably noisy? It's like comparing different technologies and using numbers that don't mean the same thing. I've been reading that camera makers have implemented film-like noise somehow. This is certainly better than the banding we've seen in certain situations but it's the chroma (color) noise that makes the biggest problems.
I've printed indoor E-1 (using flash) photos on 13x19 paper and found them to be quite acceptable, as are the outdoor photos. Are they exquisite and flawless? No. The noise is not really visible and I can only guess that the combination of photo processing and printing evened out the noise so that it isn't noticeable. For that matter, how would a 14 MP point-and-shoot compact have good 8x10 or bigger output? The TV shopping channels almost always have huge prints from so-so point-and-shoot cameras, so something has to be happening.
I believe that there is a point where the noise will be so visible that it's unacceptable to everyone. In certain industries, almost any photo noise is too much, which is why fashion uses medium format and studio lighting. I've even seen shoots where they use lighting during daylight. Even the E-5 has amazing image quality with studio lighting. I'm sure Popular Photography would disagree.