I made some pretty strong claims about the image quality of the Leica Q. So here are some comparison tests with the Nikon D750, which up to now has the best 24MP 'full-frame' image quality and ISO performance I've ever seen. (To see a comparison between the D750 and the Sony A7 II - CLICK HERE)
Here is ISO 100 - jpg. and raw
As you can see, pretty close. It is however worth remembering that the Leica has no AA filter on the sensor whereas the Nikon does and the Leica 28mm prime is a better lens than the Nikon 18-35mm I used here. Incidentally both images were shot at f/8. Raw files processed in Photoshop CS6 ACR using default settings.
Below is a comparison at ISO 1600.
Here's where the Leica Q starts to make it's mark. The sharpness / noise equation begins moving in favour of the Leica. Very impressive results from both, but the Leica is a nicer rendition, especially good when you consider it's AA free.
Here's ISO 6400
Again the Leica Q comes up with a noticeably better looking file than the Nikon. I have to say I'm surprised at how good the Leica raw file is. I've included these processed from raw images (identical parameters of course) because Nikon obviously use stronger noise reduction on the jpgs. so it's necessary to make an assessment eliminating this.
Below is ISO 51200 for the Nikon and 50000 for the Leica, the limits of what they offer. I'm reluctant to offer any opinion on this because both are pretty awful. Emergency use only as far as I'm concerned.
The differences here do illustrate the slightly different priorities both companies have. Nikon are more interested in cleaner high ISO output and Leica a sharper result. However for me, I think the Leica Q wins out on both. And of course it's always a much better idea to noise reduce sharper files than the other way around.
These results certainly reinforce my feeling that the Leica Q is one of the best low light cameras out there and maybe even THE best. The combination of the 24MP 'full-frame' sensor. the fast high quality lens, the IBIS and the near silent shutter make this an ideal camera for those situations where discretion and / or high ISO capability is required.
So where do these sensors come from? To a certain extent that's not the most important thing, since how Nikon and Leica 'tweak' these is just as significant. Nikon only ever use their own or Sony sensors, so it's one of those. Leica use Sony and CMOSIS, currently in their own cameras. It really isn't that important, but my guess is that the Nikon D750 is Nikon's own and the Leica has a CMOSIS. I have no evidence for this whatsoever other than both cameras produce better results across the the IS range than the Sony A7 II, whose 24MP 'full-frame' sensor is presumably made in house. Both companies claim these are newly-designed sensors, so your guess is as good as mine.
It does of course make the case for an interchangeable lens Q more compelling, though I have to say I still shudder when I think about the dust spots that my Leicas have generated in the past. (And the Leica T suffers from that as well.) I don't know whether the lack of an AA filter makes them attract the dust more, but certainly my M8 and M9 did really good impressions of a Hoover!!
So, if you like a 28mm lens and want a superb quality, all situations camera, the Leica Q has a lot going for it. With it's lightning fast AF it really is a very slick camera that will work in pretty much any light. Many have sung the praises of how Leicas slow you down, as if that's some kind of virtue, but now you don't have to pretend you subscribe to that, the Q is a low light speed freak and you do what you always wanted to day, grab those shots as and when you see them. And much as hate the phrase, this may well be the new contender for the best 'street photography' camera out there. I have less demanding requirements for the camera, but now I can seriously consider going inside to take some shots of that picturesque English church as well as photographing the exterior. And if some cycle race happens to passing at the same time I can get a few snaps of that as well. So the most verstatile 28mm fixed lens camera ever made. And I know that's not saying a lot, but if that's what you want, this is the one.