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ND64 filter / POI test at 12,605ft

Discussion in 'Pro/Adv Discussion' started by Drone Alps, May 24, 2016.

  1. Drone Alps

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    Stuggling with the blown out whites... any suggestions?
     
    Reed L and Fplvert like this.
  2. Not A Speck Of Cereal

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    I'm confused. Is that your video, or an example of what you are trying to achieve in respect to not blowing out whites? Because it looks good to me.

    ND64? I didn't know you could get anything greater than an ND32 for the Phantoms!

    My take on the basics: when you put on an ND filter, it will reduce the shutter speed, but increase the aperture on automatic to compensate. So you haven't used the ND filter to change the general end-result exposure so much as changed the shutter speed and aperture. In other words, you can still get blown-out highlights.

    Tip: Blown out highlights means RBG values == (max, max, max) == all white, with no highlight details.

    So what I try to see if I could do is this:
    1. Regardless of what ND filter you use (if any), I would use the exposure compensation dial to reduce exposure. Before shooting, point it at the brightest point (sun or snow reflections) and adjust until the whites are not blown-out. The P3 has a setting you can turn on that shows blown-out highlights as diagonal lines to make this simple. The downside is that it reduces the shadow details, so step #2 is a hard requirement for this procedure to be successful.

    2. Then in post-processing, look for a shadow recovery option. Not all video apps have this. This allows you to bring up the exposure of just the shadows, providing more detail, without adjusting the exposure for the highlights. It is basically collapsing the dynamic range of the frame.
    Caveat: this is mostly from a still-photographer point of view, but I believe that the general philosophy applies in video processing as well. If I'm wrong, please chastise and correct me accordingly so I can learn as well.

    Note: not all dark shadows are bad. It's okay for some of them to not have detail. It depends on the contrast your shot needs. It's also tru that not all highlight blow-outs are bad, meaning that the shadow details are more important for some shots than the highlight details.

    ND filter notes: people use these for lower shutter speed in video because they desire the cinematic look that it gives with ISO and frame rate (longer discussions held elsewhere). That aspect of using an ND filter has less to do with general exposure, or in other words, adjusting exposure to reduce blown-out highlights.

    ND filters have even less to do with still photography from a drone (not a still camera on a tripod) unless you have very specific needs and are not shooting in automatic exposure mode.

    Chris
     
  3. Drone Alps

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    Thank you Chris for taking the time to respond. Some very informative advice there!
     
  4. Fplvert

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    Beautiful video DA!

    I use a Snake River Prototyping Circular Polarizing filter for snow and water. I like how it makes texture pop in clouds, too.

    P3 & P4 Series Filters
    Here's an example with no color correction using CP8ND
     
  5. Wolfiesden

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    There are 3 components responsible for correct exposure.
    1. Aperture
    2. Shutter Speed
    3. ISO

    There is NO correct set of three that will make a correct exposure. For example, lets say you are running f4 @ 125th and 200 iso. The EXACT same exposure can be f4 @ 250th and iso 400 or f2.8 @ 250th and iso 200, or f2.8 @ 125th and 400 iso. All of them will result in the same exposure, but completely different photographs or video due to the ancillary effects of each of the three components.

    The three components form a triangle of exposure that when balanced equate to proper exposure. If you close the aperture (higher number), less light gets in so you must either slow the shutter speed to allow more time for the light to hit the film/sensor or raise the iso which increases the sensitivity to light. Similarly, if you raise the shutter speed, you must either open the aperture to allow more light in or raise the iso to make the film/sensor more sensitive to the light.

    Each of the three also contributes its own aspects into the photo(video)
    1. Aperture - this controls depth of field. The smaller the hole in the aperture, the larger range of depths that will be in the best focus.

    2. Shutter speed - This controls the ability to stop motion. The longer the shutter is open, the longer the time that light can move on the sensor. This causes motion blur in stills and video. Conversely high or fast shutter speeds reduce or virtually eliminate motion blur.

    3. ISO - This controls the sensitivity of the capturing element (film or sensor). The higher the ISO rating the more grain and noise that will be present in an image or video. In virtually all circumstances the lowest ISO rating you can use is the most desirable one however there are artistic aspects to allowing some noise.

    The aperture is fixed at f2.8 for the Phantom's camera and can not be changed without replacing the lens. Therefore you can only control the other two, shutter speed and iso. So when you put the ND filter in front of the lens, its the equivalent to closing the aperture. That means either the shutter speed must slow or you must increase the ISO, or both to maintain proper exposure. Most put the ND on so they can reduce the shutter speed.

    A note on shutter speed. Since this is really the only artistic component within our control on the phantom, its the one people desire to change. Since we can't lower the ISO past a certain point nor can we close the aperture, our alternative is to use ND filters. These, as I stated above, decrease light flowing through the lens allowing the shutter speed to be slowed. This, also as explained, increases motion blur. In video, this can be desirable. A slight motion blur lends a cinematic quality to video that is akin to what is natural in film. Video shot with a high shutter speed has little motion blur and appears slightly harsh or overly alien to many. It is, of course, an artistic choice.

    For DSLRs ND filters are typically used to allow opening the aperture thus decreasing the depth of field. This allows us to have a crisp subject and throw the background out of focus yielding a nice boke affect.

    This is an example of using an ND on a DSLR. In this photo, I used an ND8 (IIRC) to reduce the light entering the lens. This allowed me to open the aperture so that the background was out of focus while my granddaughter remained sharp:
    [​IMG]
    The same shot without the ND filter on it had the background leaves and branches more in focus. This created a visual distraction in the image and reduced the subject's presence in the photo.

    So, ND filters do not themselves control exposure. They allow us to simulate changing aperture so that we can change shutter speed to simulate motion blur. If you have the camera in auto, placing an ND on the lens will cause it to automatically change settings and the apparent exposure of the image will remain virtually unchanged. Its when the bird or subject begin to move rapidly that the effect of the ND will exhibit itself.

    Hopefully this will help you understand just what the ND filters actualy do as they are generally used differently when placed on the Phantom and on a DSLR.