Fleamavic Posted at 2018-6-7 21:10
Hmmm. When I look through my supposedly polarized sunglasses in any orientation I don't see a difference...did I get ripped off or am  I missing something fundamental here? Do you only see it for some reason when you are looking through a lens...?

   

"<"A polarising filter is also an ND2 filter since it filters out half the light.">   
                 Presumably this would only apply if the orientation is correct....?"

No, the polarising filter always filters out half the light, if it is set to allow the vertically polarised light through then it will remove the half that is horizontal, and if it is set to allow the horizontally polarised light through then it will remove the half that is vertical.  Assuming that the light has a random mix of horizontally and vertically polarised light; in the case of the reflections it will hopefully remove 100% not 50%, but if you have it orientated wrong then it may remove 0%.

"Hmmm. When I look through my supposedly polarized sunglasses in any orientation I don't see a difference...did I get ripped off or am  I missing something fundamental here? Do you only see it for some reason when you are looking through a lens...?"

Polarised sunglasses should work identically to the camera polariser filter,  with the exception that you can't rotate them, they are fixed with the polarisation always vertical so that they filter out the reflections from wet road surfaces in the same way that you want to filter the reflections from the water.

If the polarising filter is fitted to the camera, and you look at the video image on the LCD screen, and you put the sunglasses in front of the camera, then if you rotate the sunglasses from normal horizontal orientation to 90 degrees you should see the image go from normal to black.  If you see it go from black to normal then you want to rotate your polarising filter until it works correctly, otherwise it will not filter the water reflections, although it will still have an effect on the sky.  This only works for polarised sunglasses.

"The farther this goes, the more I realize I don't know!"
The definition of an expert - somebody who is always learning...  and you haven't even considered what circular polarisation is yet!

Note that if you are testing with a circular polarising filter (CPL) then make sure you have it the correct way around, and if you are not sure which way it goes, put it to your eye and look through it at a mirror, if you can see your eye in the mirror then you are looking through it from the camera side.

Fleamavic Posted at 2018-6-7 19:19
I do mostly shoot stills for this mapping project, but also record overviews on video.  We are also trying to figure out if we can see amphibian egg masses in the water while moving along a shallow shore and the light is constantly changing with vegetation types, sky cover etc.

Do it at night and you can control the lighting, maybe a second drone to carry the light source.
Or choose the time of day carefully.

Polarization, with a camera IMO has a few advantages.
1. Glare, if you are shooting around water, in sun or shade, there will be glare on the water, the polarizer will remove this.  

2.  Sky, the classic polarized look to a sky, blue will darken, clouds become more pronounced.  (not as important IMO now with many of the effects that can be added).  Downside is the fact that on a wide lens
    you tend only get 1/2 of the image fully polarized, unless you have perfect placement against the sun.  So the effect can be seen more on one side than the other

3.  Leaves, so many folks miss this.  But next time you are out on a sunny day, take a pair of polarized sunglasses and look at the greens, then take them off.  The effect is most pronounced.   Enough so that I still
     carry a polarizer all the time.  

4.  Fall colors, the polarizer can do wonders again, both on cloudy or sunny days.  

Main downside is that I believe the the AF system on the P4 seems to have issues with a polarizer.  I have used both the PolarPro NDCL ND 4 series, and Tiffen straight polarizer.  The camera AF on the P4 seems to have a lot of trouble with the Polar Pro filter, missing focus more often than not.  With the Tiffen filter I don't seem to have the same problems.  

With a fully adjustable aperture on the Phantom, the main reason for ND filters on drones is not that important, where as on the Mavic and Spark you are fix basically wide open.  

But there are times the polarizer can make the scene look much better, at least for me.  

Paul Caldwell