Should i buy a new camera or a new lens?

Hello
I'm going to extend my photography kit, because there are two things i want. Now my gear exist from: canon eos 30d, canon 300mm f4 (1,4 extender) canon 10-22, canon 18-55. First, i very often switch lenses in the field, so i thought it might be handy to buy a 40d as a second body so i don't have to switch lenses anymore (almost never take them al three out in the field) And the 40d has some improvents, 10 mp, digicIII processor, liveview and better resistant to dust etc. On the other hand, i also like to photograph toads, frogs and lizards alot. With 420mm and 1,5 m focusing distance it's alright but i like to get closer to isolate them more. I was thinking of a sigma 150mm (or if i can spend some more, a 180mm) Wich i can also use for butterflies etc. Secondhand there almost the same price. What should i do, i hope you guy's can help me out! (excuse me for my english grammar)

What a great question and sorry to say IMO the answer is "it depends".

On one hand, a lens last a long time - probably longer than the life of a normal camera before technology forces an upgrade.

On the other hand, a better camera makes all lenses better and having a backup is critical IMO. Camera's are essentially small computers and can have electrical and technical issues requiring maintenance, w/o a spare you are temporarily grounded.

Since you want to get closer, I might purchase a lens. Good luck and let us know what you do; be interesting to see what others say.

If you are genuinely keen on close up and macro then in my opinion there is just no substitute for a macro lens. Other lenses and combos are capable of good results but a macro lens saves an awful lot of messing about and they give the best results. The sigma lenses are excellent value for money, I have canon mainly because I can retain AF the canon is more expensive and the finish is more durable but arguably the optics are best on the sigma 150mm. If you use a tripod and mirror lock I don't think it matters one jot which macro lens you buy (I have field tested sigma 150mm, 180mm tokina 100mm and canon 100mm canon 180mm) - it just depends on what you prefer or can afford.:)

I would buy a 40d and a set of extention tubes, i think kenko are not that expensive and work well.

The lens will last but the camera won't !!! Would go for the lens !!! btw the only non Canon lens that I use is the 180 Sigma macro !!! One sharp puppy !!!

Get the 40D and an extension tube(s).
I had that same 300 f4 and got some amazing shots of a butterfly with a Canon extension tube.

I second what Alfred said above. (and I too love the 180 Sigma). Lenses are an investment. Cameras are a cash drain. You have to have a decent camera but a great lens will survive many generations of cameras.

Thanks for the comments! I'm not going for the extension tubes, i want to focus to infinity, so you don't stuk in a really small focus range. What i have with a raynox drc-250. I'm think i'm going for a lens than.

thijs when you are using the extension tubes is unlikely focusing to infinity will be needed, always carry my with all lenses !!! Even wide angle !!

Cameras come and go, lenses last forever.

Wait, is that a country song? :)