If you do block the lens, do it with something translucent instead of something that completely blocks the light to your eye.
Your pupils work together, so if you completely block the light to one eye, it causes both pupils to dilate somewhat.
Thinking of your eye as a camera, we know that when you increase the aperture size (pupil size), it reduces the depth of focus. That is, it means that it requires more careful focus to get objects at differing distances into proper focus.
Since shooting with iron sights requires getting multiple objects at different distances into reasonable focus, increasing the aperture size is undesirable. Ideally you want your pupil to be at the minimum size possible that still allows you to get enough light into your eye to allow you to see the sights and target.
When I choose to block one eye, I use a properly positioned strip of scotch tape on the lens of my shooting glasses.
Your pupils work together, so if you completely block the light to one eye, it causes both pupils to dilate somewhat.
Thinking of your eye as a camera, we know that when you increase the aperture size (pupil size), it reduces the depth of focus. That is, it means that it requires more careful focus to get objects at differing distances into proper focus.
Since shooting with iron sights requires getting multiple objects at different distances into reasonable focus, increasing the aperture size is undesirable. Ideally you want your pupil to be at the minimum size possible that still allows you to get enough light into your eye to allow you to see the sights and target.
When I choose to block one eye, I use a properly positioned strip of scotch tape on the lens of my shooting glasses.