This motocross track is a great place for single tree shots, no wonder I keep coming back again and again. I've compiled a new series from my last year's Dirtpark infrared shots. Have patience, I'll be flooding your inbox with stuff like this!
You can find the whole series and even more infrared shots from me here!
That sounded you don't know what 'modding' and external filters are about.
When your camera gets converted with a specific internal filter, you won't need an external filter, unless you want to use a harder one than the one that got placed in front of the sensor. My D90 has been converted with a filter around 695nm, therefore the photos it takes use a significant amount of visible light (~695-750nm). If I want to reduce that to fit the currect shot (to up the contrast or sharpness for example - blue-white shots are being done best with a 720nm, black and white shots are being done best with a 830nm filter), I screw on a 720 or a 830nm external filter. With these screwed on the lens front thread, the viewfinder is becoming black, therefore the camera is only usable with live view.
I hope that made things clear. And I strongly suggest to mod a camera that has live view, D90 and D3100 are your best bets for DX (D3100 probaby only if you're into video). Liew view's contrast detect AF will solve lots of problem with the focus shift too. Believe me, you'll regret not chosing a live view one.