When doing long exposure shots, especially in strong light, light can leak in through the viewfinder and onto the sensor causing light bands over the photo, effectively ruining it.
To stop this problem you can buy a special cover for the viewfinder, or for a cheap fix, just stick a bit of opaque electrical tape over the viewfinder. It works great and the adhesive isn’t too strong, so it doesn’t gunk up the glass on the viewfinder. Sorted.
Thanks for Reading,