Recently read a thread about neutral density filters for video cameras. Have a Canon HD M500 and want to get rid of the prop movement on the video. A couple guys were discussing these filters but was curious if anyone has had good results. There's also a lot different filters from ND2 to ND400 and I know nothing about these. Lastly, what thread size do Canons use? I'm pretty sure it's a 43mm thread size.
Thanks
Oly,
Neutral Density (ND) filters reduce the amount of light available to the camera, so for the same amount of light the camera (assuming automatic exposure) will have to compensate by increasing lens aperture (reduced f-stop) or increase the time the shutter is open. The Canon ND filter is ND8 meaning it provides 3 stops of light reduction, stops are octaves so powers of 2 (2^3=8), sometimes ND filters are characterized in decimal powers (10^0.9=8), so ND8 and ND0.9 are equivalent. For a given amount of light, aperture and shutter time are inversely proportionate: 1 stop reduction = 2 x shutter time, 2 stop increase = 4 x shutter reduction time, 3 stop reduction = 8 x shutter increase time, etc. ND2 = 1 stop, ND4 = 2 stops, ND8 = 3 stops, ND400 makes no sense (log(2) 400 = no light)
According to your camera
manual (pg 104) the default exposure mode is Program Automatic Exposure, uses programmed profiles for shutter/aperture to select proper exposure setting; the addition of ND filter will cause the camera to choose a different programmed setting which is combination of aperture and shutter time. You may affect this programmed exposure setting (page 104) by changing from Program AE (P setting) to Shutter Priority AE (Tv setting), Tv setting requires you to choose shutter speed and camera will chose appropriate aperture; you'll have to experiment with shutter speeds to see what works best to minimize prop blur. Utilizing the ND8 filter and Shutter Priority exposure setting should cause the camera to increase shutter time 8x, this should reduce the visibility of the propeller (less light on/through propeller for longer shutter time)
I checked several places and Canon version of ND8 and protective cover are no longer available, but Panasonic makes what appears to be exactly same version which is
available. The camera manual does indicate 43mm threads so most any ND filter on that size will work, doesn't require Canon brand. Given that your camera provides for exposure settings (shutter priority) you may not need any filters to accomplish what you wish, I'd start with Tv=60 (1/60th sec) and see what that provides, if it's really bright and/or camera runs out of aperture then a ND filter will provide more exposure headroom.
I use neutral density filters all the time to take flowing waterfall pictures (1/2-1 sec shutter time) in full sunlight while using narrow depth of field, sometimes using 6 or more stops of ND. One trick to taking photos of landmarks where you are unable to remove people (other tourists) is to use a long exposure, 30sec or more, people moving in the picture disappear.
My GoPro Hero3 Silver arrives today (come on UPS...) and I wondered about propeller visibility, I had not thought about ND filters so now I've learned something
