CPL , ND filter or both in video mode ?

[canonuser78]

Hello guys,

Back again with a general outdoor video shooting question.
In order to avoid overexposure in daytime maintaining 24fps at low ISO ,wide open aperture, 1/50 for example ,do you use any ND or CPL (or both) filters on you lenses ?

As far as I know these filters are complementary ,the ND will reduce the brightness and CPL will darken skies for richer blues, will reduce reflections from water, cut glare from vegetation and pump up overall color saturation in the images.
Thank you,

[hsbn · Accepted solution]

If it is bright enough you can use both. But it also depends on your ND strength. CPL normally will be around 1.5 -2 stop dark. If you have 3-stop ND, then if you stack them together you'll get around 5 stop darker. If you use wide angle lens, it may show some vignette.

[canonuser78]

thank you for your answer ,I already have the CPL, i's all clear now, I need to do some tests before buying any fader ND filter. all the best,

PS: I.ve found this in the fader ND description :

 "It may not be suitable for wide angle lens <24mm,35mm film format equivalent."

Perhaps there could appear vignette problems or other unwanted image side effects (?!).I have a 16-35mm as I've mentioned .do you think that using a fader ND like this could be a problem ? Thanks,

[hsbn]

If you have a low profile ND or CPL, it would be ok to use on 16-35mm lens. BUT if you stack them together, you'll see vignette for sure. However, it may not be that bad. It's better to test it for yourself. Buy from some place you can return.

[7D5D]

Here's some interesting info and tests on CPLs, thickness and stacking:

http://www.canonrumors.com/forum/index.php?topic=11898.msg212078#msg212078

My personal experience is, I use a slim B&W CPL on my 16-35, I have no vignetting at 16mm wide open as expected,  I've never stacked filters so I can't comment on that.

[scj7129]

If you are NOT using auto focus, you can stack two Linear Polarizers, and when rotated 90 degrees to each other will create a complete blackout. So between 0 degrees and 90 degrees, you have a completely variable ND filter. Don't take my word for it, get yerself some REALD 3D glasses (2 pairs) put them face to face. Rotate one side, and you will see a complete blackout with variation in between. http://www.reald.com/

The way the RealD 3D glasses work is that each lens is polarized 90 degrees to the other. The two projectors have corresponding filters over their lenses. Your eyes see it and your brain does the rest...combines the two images. All you are doing for the variable ND filter is stacking the linear polarizing filters. I repeat: your autofocus will not work with this. You'll most likely have to do manual focus.

Cheers!