As a photography buff I have been gaining an interest in optical assembly of lenses. I was out photographing wildlife with a rented lens. It was a 600 millimeter lens that really brought the wildlife I was photographing in close for some really sharp images. The lens was fast. It had great light gathering capabilities that I would not be able to get on a cheaper lens. I rented it because the lens actually costs more new than what I paid for our used minivan!
The lens was big and heavy but very capable of letting me get tack sharp focus on the eyes of the birds I was photographing. I got some great shots of the various furry critters running around out in the woods too. The lens brought me in close even though I was a great distance away so as to not frighten the animals. Long lenses like this are the staple of most wildlife photographers. Sports photographers use them too.
I spent a lot of time looking at that big lens wondering how it was put together inside.