EOS 5D Mark II - viewfinder get darker

[MrDonutto]

Hi, when i start shooting with flash some times my viewfinder get darker and noisier,  same thing for my sensor turning of / on or taking out battery doesnt work,  it "fix" itself after some time. 

[deebatman316]

The EOS 5D Mark II is a DSLR camera with an optical viewfinder. It cannot change the brightness all it shows is the ambient lighting. If you're talking about the EOS R5 Mark II then the EVF brightness can be adjusted. So please verify the camera that you're using.