Many photographers remember the days of sitting over a light box or table with a loupe up to our eye. Thought times have changes and loupes have evolved there still is a need to keep on in your bag at all times.
The modern day loupe can serve many purposes in a photographers camera bag. Before I tell you what they are lets take a look at what a loupe actually does. A loupe simply allows you to magnify something smaller that you would like to see a little clearer.
I personally use a loupe when I am outside and want to get a better look at one of the images on the back of my camera screen. Sure screen have gotten larger but its not so easy to see the details of your image without a loupe.
Todays loupes are designed to cover the lcd screen on the back of the camera as well as block out light from the outside from interfering with your viewing. This allows you to get a better look at the image on the screen, is the exposure proper, is your composition on but more importantly is it in focus.
Not only is it a great way to shield your lcd from the sun for still images I think it is imperative for capturing video. Using a loupe for video helps you make sure you are in tack sharp focus as well as able to follow focus a moving subject.
Loupes can range from $50 to $500 depending on the manufacture and magnification quality.