Blocking the viewfinder for long exposure
I have a H5D, but the question should apply across the board. Are there any favorite simple methods out there for blocking off the viewfinder to prevent light leaks with extremely long exposures? Is this really necessary with MF? I have only had an issue with fogging once or twice with long exposures (30+ seconds). My Nikon 810 has an eyepiece shutter, but no such thing exists for the H5D. One photographer I know simply puts his baseball cap over the camera.
Re: Blocking the viewfinder for long exposure
I carry some small packable quick-dry towels in my pack to wipe off my H4D when it gets wet. They're dark in color and don't pass [much] light, so I just drape one of those over the lens mount/camera/back/viewfinder. Not the best solution if it's windy though. The other drawback is I've found this method usually draws attention and people come up and ask me what I'm doing with things draped over the camera/tripod. Other times, I just hold my hand behind the viewfinder (without touching it to avoid camera shake) for exposures of a minute or less.