Hello, I use a 10x infinity objective as a condenser in a optical trap setup. The collimated forward scattered light is then focused with a 40mm lens onto a QPD. This is the imaging techqnique. There is also BFPI, and I am not clear on this method. My understanding is that I need to image the back focal plane of the 10x infinity objective by inserting another lens. Then use the 40mm lens to image onto the QPD. For cell/vesicle level work ( not single molecules) what advantage does this bring? More importantly, does the data processing change? I use the power spectrum method to calibrate.