Perchance, has anybody else experienced this issue? When I lock-up the mirror - a feature I use all the time with landscapes and macro - the shutter doesn't open. It fires, but the shutter moves from first curtain to second curtain without ever opening. I just get a firm click, regardless of shutter speed. This only started happening in the last few months. I can continue shooting without the mirror lock up but I'd prefer to get it repaired if nobody has a quick fix here. Thanks.