What is the difference between 見てない and 見たことがない?

Question

The title says it all, what's the difference between 見てない and 見たことがない?

Lately, I've seen japanese people using 見てない to express that they have never seen something, eg:

この映画は見てない。

But I thought that 見てない would be used in the following fashion:

今、映画を見てなくて、晩ご飯を食べてるよ。

And how different it is from:

この映画を見たことがない。

is the usage of 見てない a set phrase or something?

Answer 1

見たことがない means "Someone has never seen something ever."

見ていない is a negative progressive form 見る and it means "Someone isn't seeing something" . 見てない is omitted い.

見てない also has the meaning "Someone doesn't(has not) see(seen) something ", but the nuance of "ever" is less.

For example, you can say 彼をまだ今日見てない、but 彼をまだ今日見たことがない would be unnatural.