400mm

[Omag 2.0]

I'm sorry, but the FZ7 doesn't have exchangable lenses. You'll need a dSLR for those lenses.

Ex. Canon 400D - 450D - 40D -... Nikon D40 - D80 - ... Pentax, Sony and Olympus are other brands...

As far as the lenses themselves, you need to know your camera and then read reviews about the lenses. Set your budget and choose the best one... But be prepaired that you'll get what you pay for. Cheap often means less quality. So read, read, read...

Not every lens goes on every camera. Canon, Nikkor, Zuiko, Pentax and Sonylenses only work on the camera's they were designed for.

Tamron, Sigma and Tokina build lenses for different camera's, but even then they are interchangable. You can't put your Sigma for Canon on a buddies Nikon camera.

literature: www.photozone.de

PS: your FZ7 allready has a 400+ mm lense attached to it.

[Omag 2.0]

To get really nice shots of contrails and planes that high up, you'll have to look into telescopes. But that's a whole different story...

[Vapour01]

Just make sure you avoid crossing into digitial zoom, if you do you'll regret it!