Desculpe, mas a 50D não possui melhor qualidade de imagem em relação a iso's altos do que a D300s. Inclusive falando a nível de sensor tanto a 50D quanto a 7D ficam abaixo dos sensores da D300s, D90, D5000.
Bom, se você fala, quem sou eu para poder comparar o resultado de uma 7D com a série D300s, D90 e D5000. Aliás, alguns reviews também erraram.
Porém, o teste prático de uma 7D em relação a uma D90 em condições iguais e D90 com lente bem superior não dá nem para comparar. Mas, pode ser que eu tenha errado em algum ajuste na D90.
Ao final do review abaixo tem alguns samples de imagens.
http://www.imaging-resource.com/PRODS/E7D/E7DA.HTMDetail comparison. Since there really is no true comparison to the Canon 7D's 18-megapixel sensor, all I can do is compare it to its nearest competitors in the market, one 15, two 12, one 21, and one 24-megapixel sensor. The latter two are clearly superior thanks to their full-size 35mm-equivalent status, and they should be superior. The 7D holds up just about right against its lower-res foes, even the full-frame Nikon D700. At 3,200 and their highest settings, you could convince me that raising the resolution would produce almost the same result, but at ISO 100, the Canon 7D has the lead. Also note that the Nikon D300S and D3x top out at ISO 6,400. All six are cameras that get our highest recommendations.
======
Image quality finishes the list of the Canon 7D's strengths. Canon managed to exceed the resolution of all competitors while improving image quality at all ISO settings. Even the 12,800 setting is usable when printed at 8x10, straight from the camera. Add some noise processing, and you have a very clean image. That's remarkable, and it makes the Canon 7D a great choice for low light shooting. The Canon 7D's Movie mode is quite good, despite the lack of continuous autofocus, and a viable alternative to the more expensive EOS 5D Mark II.
Fonte: imaging-resource.com
Espaço Canon