D3100 versus D700 – How many stops apart at high ISO and in low light?

The D7000 is shipping, so there is a flurry of OMG! posts regarding the D7000 noise reduction and how amazing it looks at 6400 ISO. Some are congratulating themselves over how close they are (presumably to justify the purchase of the D7000, which actually has many reasons for acquisition – none of which include matching the D700 at 6400 ISO :-)

My favorite test site, imaging-resource.com, does not yet have D7000 jpegs posted, so I thought in preparation for my analysis of that pairing, I would do the D3100 in a bit of depth. Just a bit, as you will see.

I think a camera must do two things at high ISO to be a contender:

• Control chroma noise … huge blotches of blue or yellow make recovery of a good images essentially impossible. It was the crhoma noise starting at 800 ISO that made me finally replace the G10 as my concert camera. I really miss that thing, but it pretty much sucked.
• Retain as much detail as possible. And not just high contrast details … everyone seems to be getting good at that trick. No, I want to see lots of low contrast details too. The classic being texture in hair. I *hate* helmet hair.

So … with that goal, let’s take a look at one crop set based upon the imaging-resource mannequin files.

My analysis:

• Generally, they all handle high contrast details adequately. Even 6400 on the D3100 shows a decent depiction of eyelashes etc.
• Hair is badly clumped on the D3100 at 6400 ISO. This would look good enough at web sizes, but even an 8x10 would show the helmet look.
• Hair at 3200 in the D3100 is not bad, but there is still considerably more clumping than on the D700 shot.
• The D3100 1600 ISO shot looks good. The details are very similar to the D700 at 6400 ISO, although the hair does look a bit coarser than on the D700. The skin and eyelid textures are about the same. The D700 even has a trace more noise in the shadows, but not enough to show on any normal print, even a very large one.

My conclusion is that the D3100 shoots at 1600 ISO about where the D700 shoots at 6400 ISO, presuming that you need to retain a lot of low contrast details. If not, then there is only about a stop of difference.

I suspect that the D7000 will come out pretty similarly. Right now, we’re seeing test examples that are all blurred backgrounds and high contrast, large details. No challenge at all for any modern DX camera. We;’ll see how the imaging-resource torture test fares …