It all depends on where you learnt your English, americans don't speak properly nor spell correctly.
Lens is the correct English spelling, lense is something the americans came up with. Me I can never remember which is which so often spell it both ways.
Seems more subjective to me!! (but a more objective view is that, without wishing to be didactic, as it comes from the Latin "lens" and we in England have been using it since before the US or Oz was invented "lens" it is!)
Although, if you have more than one, it shall be LENSS. Most likely, someone began the 'lense' usage because of the plural version. I try not to concern myself as much with its spelling as its use.
I spell it with the 'L' emphasized expensively.
In a group of LENSES you pick out a single LENS. Unfortunately many people just copy what they have seen somewhere, thinking that it is correct. Happens a lot in life too.
Jyrgen, in English, there are no apostrophes in plural nouns, unless possessive.
By the way...
americans don't speak properly nor spell correctly
Eh... you were looking for...
Americans neither speak properly nor spell correctly,
or
Americans don't speak properly or spell correctly.
In either case, I'm American, and I do both extremely well. "Lense" is listed as a variant at Merriam-Webster, and they usually note if something is incorrect. Princeton's online dictionary has it defined as well. For my money, it's "lens," and it seems ignorant to just drop an "s" to make the word singular, but I'm not arguing with the dictionary people.
The only "lense" in the OED is an archaic verb meaning "to make lean". Merriam Webster lists "lense" as an accepted spelling, but then again it also has words like "stick-to-it-iveness" and "guesstimate". That's why I call Webster's the Scrabble dictionary.
Eric S wrote:
The only "lense" in the OED is an archaic verb meaning "to make lean". Merriam Webster lists "lense" as an accepted spelling, but then again it also has words like "stick-to-it-iveness" and "guesstimate". That's why I call Webster's the Scrabble dictionary.
Fair enough, but Princeton's dictionary is usually strict. Like I said... it's "lens" imho. But it seems the jury's out due to collective ignorance and apathy towards spelling/grammar in general (if I hear "irregardless" one more time... ). Orwell's "Politics and the English Language" ought to be required reading at every grade level.
'Lens' or 'lense' aside, I often find people here are careless in their posts when it comes to spelling, or maybe they never learned to spell correctly. I am not a native speaker, and I always check my spelling before I post anything. Call me old fashioned.
BTW, the correct spelling is LENS, LENSES when more than one.
"Lense" is listed as a variant at Merriam-Webster, and they usually note if something is incorrect. Princeton's online dictionary has it defined as well. For my money, it's "lens," and it seems ignorant to just drop an "s" to make the word singular, but I'm not arguing with the dictionary people. 
). Orwell's "Politics and the English Language" ought to be required reading at every grade level.