Thank you very much for the detailed advice and information. Now I have an absolute clear picture of ND Filters and what it does.
On a side note, regarding still photography, would Auto Mode perform just as well as Manual Mode ? I mean, I don't think I ( or most people for that matter ) would have the luxury of our own time meddling with the settings to make sure it's the correct one in Manual Mode, rather I believe when most people is on the job, they just take pictures / shoot videos on Auto, would Auto works just as well ?
Okay... well different camera makers have different configurations in their camera's auto settings. It is never one size fits all, between them or even with one camera in all lighting situations. I'll try to simplify it for you.
When set to auto and in good to ideal lighting situations, the auto setting works very well. With that said, it all depends on the user and what they are filming and where. Auto takes and average all over reading of the lighting value and then tries its best to give you an average exposure for what you are pointed at.
Lets look at some examples so that you have a better understanding of what is going on in Auto. Say you are filming a white person against a white background and a black person against a darker background. Auto setting will or should, give you a very good outcome because it takes the overall light coming into the camera and gives an average exposure to take into account the largest area of light and compensates the exposure setting for that situation.
Therefore the white person against a light background means that the light background will trigger the auto setting mechanism to reduce the amount of light coming into the camera sensor, to help give the light background a correct exposure. In doing so, it will of course allow the white person's skin to also be more or less correctly exposed. The same goes for a darker background and a black person. The auto meter will take the major area, which is dark, and compensate for the darker area and allow a little more light to come into the camera, giving an average overall exposure that should show a nicely exposed image.
Now, where the problem with auto exposure is when there is a large disparity between light and dark areas. Let's now take that black person and put them against the light background and the white person against the dark background. The auto setting will again sense the major area of light, which if the light background, will expose for that and tell the camera to darken the overall setting. This will give correct, darker exposure for that large light background, but the black person's skin will also be darker, rendering them under exposed or too dark for a correct image exposure of the person.
Same for the white person now against the dark background. The auto meter will sense the overall darker image and allow more light into the camera to give a correct exposure for the main element, that being the dark background. So the camera will brighten things up a bit but in so doing, will now over expose the white person's skin and causing them to become burned out. There is no perfect setting for such situations and no camera is capable of giving a single correct exposure setting, in the way our eye can see the scene. Our eyes have a far, far greater dynamic range than any current camera made for consumers.
That's why we shoot about 5 different exposures at the same (roughly) time when trying to get a proper exposure for a difficult scene like that explained above. Then we sandwich these five images and take the best exposed sections of each image to suit what we need for the perfect HDR manipulated photo. You can't do that with video, only still images.
Therefore, when you shoot in auto and you have a lot of sky in the scene, the auto setting will tell the camera to darken down the scene, correctly exposing the sky but then making the ground too dark for a correct setting. If you have a lot of darker ground in the scene and smaller area of bright sky, the auto setting will lighten up that darker ground to give it a correct exposure, though by doing so, it will over lighten or burn out the portion of sky in the framed scene. You compensate for this with a graduated filter, so that the upper section is darker and the lower section is clear. That will fool the auto meter into giving the scene the overall correct exposure. That is, assuming the framing you did allows for half the sky and half the ground in the shot. This immediately goes wrong if you were to raise or lower the camera position as you flew. Again, even a manual setting can not compensate for this situation.
Another problem with auto is when we have plenty of sunlight on the ground with the sun behind us as we fly and film, which would give a very good all over exposure for both sky and ground. Now let's assume you then do a slow 180 degree turn into the sun. As you get closer to the sun the auto setting will begin to darken down everything until it faces the sun, when it will expose correctly for the sky, but making it dark, due to the sun getting in there and the ground will be very dark. If you used a manual setting for this, you could adjust as you came around into the sun and begin to open up the aperture and you turned into the sun. This would continue to give you a good exposure for the ground but it would of course burn out the sun and sky, when turned into the sun.
Again, there is nothing that can be done about such a large dynamic range of light to dark, in such a scene. Therefore when filming in such a situation and in a manual setting, you must divide up the light and dark areas and use a mid range exposure to try and get the best of both extremes of the dynamic range. So the dark earth would be a little darker than would be perfect and the sky portion would be a little lighter than what would be a perfect exposure. So you need to choose what is the best average exposure for both light and dark areas.
As you can see, there is no perfect setting for all lighting and framing situations. However, if you are shooting manual, you can at least do some compensating while flying to adjust the aperture to try and optimize your overall exposure. If you are careful and choose wisely what direction you fly each time you begin to record, then you will probably get a good overall exposure if you opt for the Auto setting. However, that depends largely on you for choosing the direct to fly and what you are going to film each time you press the record button.
As you can see, there is no perfect setting for all situations you will encounter as you fly. That's why it is good to understand lighting and dynamic range of your subject matter and be mindful of how and what you are shooting. Only then, will you be able to correctly (hopefully) choose which setting and mode you should have the camera set to. This was not an easy nor quick question to answer for you and maybe I did not simplify it for you, but I hope it helped, so apologies for such a long post. I suppose to sum it up regarding still photography, shoot in auto and see how it looks. If you need to compensate lighter or darker, then make adjustments to do that with the plus and minus settings, plus adds light minus takes light away. The other thing that would be best all-round, for difficult dynamic range situations, is to shoot in HDR and use 5 images at a time. Three could work in many situations but with five, you have probably cover the entire dynamic range to give you the best chance of a very good final image. Now you have a better idea of settings for both video and still image capture.
