Originally posted by EHogan Thanks for the quick reply! The NR is turned on (auto). I'm (maybe obviously) new to long exposures and hadn't heard of covering the viewfinder, so its been completely uncovered. I just did some quick research and I bet this is exactly the problem. I'll do some more tests and report back, but in the meantime I welcome any more insight!
Yes, when doing long exposures, the mirror is up and the foam seals will stop light getting from the viewfinder to the sensor and ruining the shot....but only up to a point
The problem is most apparent when the sun is bright and behind you....so shining right into the viewfinder.
The best way to deal with it is to remove the viewfinder eyepiece and slot in the viewfinder cover (little plastic thing that comes with the camera), but in practice, and depending on length of exposure a thumb over the viewfinder or hand shielding it will usually work.
ps. there is also a good reason why long exposure photographers chew gum !. Just make sure not to actually touch the camera during exposure.