When he notices that the camera-man on set is an alien planning on taking over the world, the percipient lead actor must convince the rest of the crew to save the planet.

Dig it, leaning towards:
“An indie film star and his reluctant crew must save humanity when an out-of-this-world cameraman attempts to steal the show – and the planet.”

Make this yours, take care.

Maybe emphasise that the actor is in the biggest production yet. For example "When he notices that the camera-man on the biggest film of his life..."

Also, could be a funny twist if the reason no one believed him is that everyone else is an alien too and they're trying to keep the secret - not really a logline addition though.

Overall I really like the concept and think it'd be really funny.

Be careful on the length of your piece, this story could be written at any length.

Aside from that it's a really well written logline.

Putting 'When he' at the start is a little confusing. Personally I would put that it is the lead actor first. Otherwise I like the idea. Nice logline.