Preventing Underexposure from Stray Light

As photographers we are obsessed with light — but it's a rare that we encounter too much light which cause our shots to be underexposed. It's not supposed to work that way, is it?

Here's a botched shot from last Sunday:

It's obviously massively underexposed... but what caused the automatic metering to fail so drastically? The clue is in the top corners. I was using a polariser and ND8 filter stacked with the polariser closest to the lens. In the top corners you can make out the shadow of the polariser's notched edge being reflected in the ND8 filter. Therefore the light was from coming directly behind the camera, bouncing off the nearside of the ND8 filter. Because I didn't want my own shadow in the shot, I was standing some distance away and triggering remotely. But if a strong light source (like the sun) is coming from directly behind the camera, it can fool the camera's light meter into underexposing the shot.

Here's what it should have looked like (by covering the viewfinder as described below):

The solution is incredibly simple. Most cameras will come with this little viewfinder cover that is usually attached to the camera strap:

By removing the viewfinder eyepiece

You can slide the cover down over the eyepiece and prevent any stray light from entering the camera during an exposure