What does "let alone film one" mean?

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hello,
Please tell me the meaning of the sentence below
1.We failed to lay eyes on a tiger during our expedition,.
I don’t understand the meaning of ‘‘LET ALONE FILM ONE’’ Please tell me.Thanks in advance.

2

I think,

We failed to lay eyes on a tiger during our expedition = We didn’t succeed in finding a tiger during our expedition
LET ALONE FILM ONE = Not to mention film one

Haihao