In a comment to the previous post, a reader challenged my assertion that the NEX-7 is a terrible lowlight camera because of high noise level above ISO 400. I’ve conducted some experiments to demonstrate what I’m talking about.
Because noise needs to be evaluated at pixel for pixel or higher resolutions, I thought it would be best to compare the NEX-7 to another 24 megapixel camera. Fortunately, I had one available: the Nikon D3x. The D3x’s low light problems are well-known. Even Nikon acknowledges them tacitly by using identifiers such as “H 1.3” for settings above ISO 1600.
As you will see, the NEX-7 has low light performance that is inferior to the D3x. At one level, this is to be expected, since the D3x is a full frame camera, and therefore has sensor sites with approximately
1.5 [correction: 2.25] times the area of the sensor sites on the NEX-7. On another level, it is a surprise, since it’s been almost 3 years since the D3x came out, and technology marches on.
On to the test. I put a Leica 24 mm f/3.8 Elmar M ASPH on the NEX-7. Multiplying 24 mm times 1 1/2 gives 36 mm for the focal length with the equivalent field of view on a full frame camera. I didn’t have a 36 mm lens, but I did have an AF-S Nikkor 35mm f/1.4 G. I put it on the D3x. Serially, I aimed the cameras at a dimly lit bookcase, set the ISO to 800 (on the NEX-7, 800 is the next ISO above 400), focused with live view, set the aperture to f/8, and the shutter speed to an eighth of a second.
I converted the images from raw format in Lightroom 3.6, turning off all noise reduction, and leaving sharpening at the default.
Here’s the picture with the NEX-7:
Here’s the one with the D3x:
In order to look closely at the noise, I expanded the images to a magnification of three, using nearest neighbor, which will give a square array of nine identical pixels for each pixel in the original images.
Here’s the blowup of the NEX-7 image:
Here’s the expansion of the D3x image:
You can see that the NEX-7 has more noise in general, that the noise patterns appear to be coarser, and that there’s more color noise. These differences are more apparent before the JPEG compression that I used to post the images on the blog. I always learn something from reader’s criticisms, and I retract the word “terrible” in the previous post. Let’s say that, with cameras like the D3s available, the NEX-7 is far from the best choice for a low light camera.
The NEX-7 image appears to be the same or maybe slightly sharper than the D3x photograph, even though the sensor is smaller. It’s very close, though. It looks like the Leica glass is able to overcome the Nikon’s sensor size advantage. Also note the greater color fringing in the Nikon image. Sure makes the NEX-7 seem like a bargain, even if the Leica lenses aren’t.