I got a cheapo P-Series Equivalent Neutral Density Filter - ND2/ND4 from here. http://www.cameras-online.com.au/massa-p-series-neutral-density-filter-nd4.html
Just stuck it to the outside of the focus lens with blutack.
I have to tell you though, it does dull the sharpness a bit, nothing major but it does reduce sharpness. I haven't tried more expensive filters so it may just be this cheapo. I really wanted to at least test both the ND2 and the ND4 before buying a better quality filter.
After some research it appears that only the really expensive Heliopan (+$400) is free of loss of sharpness.
Here are my settings after calibration for those of you who were asking for them by private message.
Color Temperature - Normal
Brilliant color - ON
Dynamic Black - ON
Gamma - 2.4
Color Temperature Fine Tuning (used for adjusting grayscale)
Red Gain - 47
Green Gain - 50
Blue Gain - 47
Red Offset - 256
Green Offset - 256
Blue Offset - 260
Color Management (used for adjusting color balance)
Red - Hue 70 - Gain 50 - Saturation 72
Green - Hue 50 - Gain 65 - Saturation 65
Blue - Hue 35 - Gain 70 - Saturation 60
Yellow - Hue 18 - Gain 65 - Saturation 55
Cyan - Hue 72 - Gain 55 - Saturation 70
Magenta - Hue 74 - Gain 60 - Saturation 85
Edited by j2037 - 10/30/12 at 10:24pm