Canon schreibt dazu:
Zitat:
Live View and sensor protection
If you are using the Live View function to compose your images and judge exposure, then where possible, you should keep the duration as short as possible. This is because when shooting in Live View, the sensor is active and is therefore generating heat. Over a long period of time, this heat can build up and may start to degrade the image quality by increasing image noise. To help to avoid this there is a cut-off on Live View that, after an on-screen ‘temperature’ icon warning, will turn off Live View when the temperature becomes too hot and disable it until the camera’s internal temperature decreases. To ensure you avoid any possible problems with ‘overheating’ you should remember to only use the Live View function for as long as you need it.
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Using Live View and the sun
When photographing sunrises and sunsets, it is quite common to make use of the Live View feature of EOS DSLRs to judge exposure and to help you to place Neutral Density (ND) graduated filters. In most shooting situations this is perfectly fine but, if the sun is very large in the frame, you should take extra care when making use of Live View. Live View lifts the camera’s mirror out of the way, and opens the shutter, thus allowing light to pass through to the CMOS sensor where it can be displayed live on the rear LCD display. If the sun’s rays pass through the lens, they are being focused towards the sensor and can generate excess heat. So, in the case of with a frame-filling shot of the sun, this could lead to some damage to your camera’s sensor – thus, when using Live View in such a situation, caution is advised.
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Kurzübersetzung:
Der Sensor hat einen Temperaturfühler. Wird's zu heiss, schaltet die Kamera ab. Trotzdem warnt Canon vor Aufnahmen direkt in die Sonne mit langen Brennweiten (Sonne bildfüllend) mit Liveview und rät zur Vorsicht (kann den Sensor beschädigen).
Wie Toni schon schrieb: Da es im Forum einige Jammersthreads über z.B. das silberne Exterieur des 70-400 gibt aber keinen einzigen "Hilfe, mein Sensor hat ein Loch..." scheint das Problem nicht sehr gross zu sein.