When taking photographs, the eye prefers visual input and the one you should be using when looking through a viewfinder and taking photos is the dominant eye.

Reddit user ElementK shares an easy way to determine your dominent eye. ElementK's technique is one of many but it's one of the easiest to do:

Extend both hands forward of your body and place the hands together making a small triangle (approximately 1/2 to 3/4 inch per side) between your thumbs and the first knuckle like this.

With both eyes open, look through the triangle and center something such as a doorknob in the triangle.

Close your left eye. If the object remains in view, you are right eye dominant. If closing your right eye keeps the object in view, you are left eye dominant.

Give it a shot, and see your results. Reddit via DIY Photography

Photo by Julia Lamphear.