The noise levels on the Canon 40D are quite good. However, at ISO 800, the grain becomes very noticeable. For street photography, I don't mind this effect. However, for nature and wildlife, I prefer a cleaner look. I needed to use ISO 800 with my 400mm 5.6 to attain a fast enough shutter speed to freeze the flight of the bird. Yet, when I reviewed the RAW image zoomed to 100%, I was disappointed with the noise levels (see image A). Thankfully, the solution was a fairly simple one. I purchased the "Neat Image" Photoshop plug-in for about $30. As you can see in Image B, the software made a dramatic difference, removing most of the noise artifacts. If you have some grainy photos buried in your hard drive, you may want to give this software a try.