I have bought a secondhands Canon 600D. Now, I've noticed that I have a problem with the viewfinder.
When I look through the liveview en adjust my exif manually (F, Iso etc) it affects how my picture is going to be.
If I do thesame while looking through the viewfinder it doesn't affects the image, but if I shoot the picture, it's all different then how it looks through my viewfinder.
Have I missed a crucial setting on my camera or is something just broken?
LiveView is showing you how the camera electronics see the image, so when you adjust the image manually (only changing one variable) how the image looks will change since the camera is not adjusting for correct exposure.
When you look through the viewfinder you are just looking at the the real world through the lens.
If you are in Auto or P mode the LiveView and viewfinder should both look close to how the recorded image looks.
So, if I am understanding correctly what you are stating, there is nothing wrong with your camera