Be careful when buying before sensors with increased dark noise

The literature (Stefan Gross, "The Professional Guide
Canon 5D Mark II, Data Becker) confirms what some users
have even found: In some models, this
otherwise excellent camera sensors with visible elevated
Dark noise installed. Since Canon No customer specification
published this characteristic of sensors, is an exchange
more or less guaranteed to miss.
The increased dark noise bothers normally little. But who
long exposure times required (in seconds or even minute
area) and the built-in noise reduction off
wants to leave, the camera should test immediately after purchase and
possibly return.

The test is quite simple:
Off noise reduction for long exposure -.
- Install Lens Cap
Activate sensor cleaning -
- Dark recording with 60 s exposure time
The increased noise manifests itself in a variety reddish brown
Spots that are distributed more or less erratic over the image.
The informed customer can use for comparison shots to get
is where the sensor is OK.