Well, look on my answer in this
thread.
I think there is some confusion about utilisation of ir-
cut-off-filters on webcams.
If you work with ir-LEDs no matter if 750nm or 850nm, you need to put off the ir-cut-off-filter from webcam as normaly they start up from 700nm, if you want to conserve the full light intensity.
If it works yet, it's because off weakness from this in-build filters.
Ir-pass-filters for cameras are usually quit expensive, as they do have to possess good optical quality. This is not necessary for tracking. There are good solutions with developed film or multiple coloured film layers that works fine.