I bought a variable neutral density filter here in OKC, and now I am wondering if I made a wise purchase. I am now shooting in RAW, and I use Photoshop Elements 10. With that in mind, is it even necessary for me to raise and lower exposure with this filter since I can do that in PS 10? I am planning to shoot in manual mode, then raise and lower exposure with the filter. Is this over-kill? I can already bracket exposure using my D90 camera. Is there an advantage to altering exposure and leaving the f-stop and shutter speed fixed? Please advise.