I just got an f4. First thing I did was test all the buttons and functions. I have a question for anyone with an f4. Is the mirror lock up lever supposed to be able to move the mirror without the exposure preview button pressed down? I can't lock the mirror without pressing the button and rotating the lever but I can still rotate the lever (not all the way) without pushing the button in, causing the mirror to come up with the button unpressed, however the mirror will come down as soon as I let go. Will I need repairs or is this normal.