My Canon EOS 5D Mark III is producing highly grainy images?

[jimmynhp]

I bought my Canon off eBay. I have been using it for a few weeks and have noticed the image is sometimes very grainy. Is this a fault of mine or is it the camera? My serial number has been clarified by Canon. I am shooting in RAW.

I have noticed it being grainy when shooting with ISO 12,800, even being in well lit areas. But looking at videos on YouTube, the quality should only start to deteriorate after ISO 25,600?

[hsbn]

I think you expected too much from the camera. You can not judge the photo by viewing on Youtube. You can resize your photo to the same size as the youtube video and you'll see all the noise disappeard. ISO 12800 has lot of noise and it is normal. For me, I will only shoot at ISO3200 or higher only when I don't have other options.