What ND filter for motorsports panning

[SpeedySwede]

What ND filter would you guys recommend for motorsports panning shots during the daylight or do you think it is even needed. I'm mainly looking to use for some powerboat racing. I have a CP that is worth 2 stops. I would probably be looking at shutter speeds around 1/25 to 1/80.

[DC Fan]

Filter? None. Shutter priority and a low ISO on bright days.

http://www.fansview.com/racing/05222008b0235.jpg

Camera Model: Canon EOS DIGITAL REBEL
Image Date: 2008:05:22 11:40:53
Flash Used: No
Focal Length: 120.0mm
Exposure Time: 0.0050 s (1/200)
Aperture: f/13.0
ISO equiv: 100
White Balance: Auto
Metering Mode: Matrix

http://www.fansview.com/racing/07022008a0427.jpg

Camera Model: Canon EOS DIGITAL REBEL XTi
Image Date: 2008:07:02 11:41:59
Flash Used: No
Focal Length: 240.0mm
Exposure Time: 0.017 s (1/60)
Aperture: f/22.0
ISO equiv: 100
White Balance: Auto
Exposure: shutter priority (semi-auto)

[SpeedySwede]

Thanks, those look great. I was worried about getting up over f/16 with a 100-400 but for boats it looks like I can probably get by with the couple stops from the CP filter if I need it.

[andrewc]

Panning with a CP filter could cause funny effects.

[DC Fan]

Boats? On an overcast day, no filter and higher ISO.

http://www.fansview.com/racing/07042008a0228.jpg

Camera Model: Canon EOS DIGITAL REBEL XTi
Image Date: 2008:07:04 11:09:18
Flash Used: No
Focal Length: 170.0mm
CCD Width: 4.30mm
Exposure Time: 0.013 s (1/80)
Aperture: f/14.0
ISO equiv: 400
White Balance: Auto
Metering Mode: Matrix
Exposure: shutter priority (semi-auto)

[Stump556]

What a cool shot on the water!! I love it

[TouringBubble]

Panning with a CP filter could cause funny effects.

I think I figured that out the hard way yesterday ... :( The AF was going nuts, but that may not have been the filter.