Why is "lens" singular and "lenses" plural? Why isn't "lens" the plural of "len"?

@Callmyname might be, but we don't say hand me that "jean" we say I have on "jeans" when it's only one thing, but we also say "all their jeans are half off!"

@Callmyname who calls them a jean and a jean, though? We say one leg of my jeans is torn not my jean is torn. We say a pair of jeans, but we also say a pair of pants, and the same thing applies. We don't say my left pant is torn; we say my pant leg is torn.
We also say TV set despite there just being one TV.

@boklenholley7 But yet, the plural of deer is deer, and the plural of moose is moose.

@Callmyname I've got to say this is one of the most interesting conversations I've had on here in awhile :p

@Callmyname definitely! Especially when no ones getting mad haha. How can you get mad about the use of a word?

@Callmyname totally agreed!