The most common and most likely answer to this crossword clue is the 7 letter word FISHEYE
F
I
S
H
E
Y
E
Buddy explains!

The straight part
We know that "Lens" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lens = fisheye.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FISHEYE mean?
FISHEYE noun- An unfriendly or suspicious glance.
- An undesirable effect in paint, particularly automotive finishes, normally caused by oil or other contaminants on the painted surface.
- An undesirable dull appearance in the table of a diamond that has been cut too shallow.
- (of a lens) Covering an extremely wide angle and producing a circular image that is distorted towards the edges.