Camera's eye (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">camera's eye</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lens that I've seen before include "Focussing glass" , "Optical refractor" , "Light-focusing device" , "Part of photographer's equipment" , "One could project a picture" .)