Hi,
This thread is a very nice idea. A couple weeks ago I replaced my ageing 450D (EF-S 18-200 + EF-S 17-55/2.8IS) by a 6D + EF 25-105L and ... wow, what a difference! Color, dynamic range, high-ISO performances and image quality are so much better that I feel again that I am clearly the main limiting factor to achieving better shots. Below are a few samples from my first field trials last week in Blois, near Orleans (France).
1/1250s, ƒ/5, ISO 100, 105 mm

1/13s, ƒ/4, ISO 12800, 24 mm

1/8s, ƒ/4, ISO 12800, 24 mm

1/8s, ƒ/4, ISO 12800, 24 mm

All the night shots were taken handheld, a habit (some would call it a bad one, but not everyone like carrying 10 kg of equipment around) I caught while using the EF-S 17-55/2.8IS. The 24-105 L clearly shows its limitations as I had to use a high ISO setting in order to limit blur, but the image quality suffered quite a bit in the process. Don't get me wrong, I think the 6D has some really outstanding low-light performances, but for the sake of e.g. dynamic range, noise, sharpness etc it is still better to reduce ISO whenever possible. For instance, I found that the built-in noise reduction processing considerably reduces the finesse of image features.
To solve this particular issue I acquired an EF 35mm ƒ/2.0 IS USM yesterday for low light works. This glass should provide me with a 2.5-3 stop advantage over the 24-105L due to the combined extra stops gained from the better IS and the larger aperture. I’ll see in the next few weeks how the pair handles, and from my first tests I definitely have great expectations.
