Focal length on a crop sensor camera

Thanks for the answer, I just wanted to check and make sure that I wasn't understanding it wrong. I'm only worried about effective focal length.

For explanation though, I should have mentioned that this is for video work only. I wont be using such a long combination for photo work for, well, the reasons as mentioned above. Basically I need a lot of reach for shooting video of very small wildlife, particularly birds such as sparrows and dunnocks.

Anyway, my question was answered nicely so thank you