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Use of ND filters

Discussion in 'Pro/Adv Discussion' started by photodhill, Oct 5, 2015.

  1. photodhill

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    I know a lot of you use ND filters, I don't know what you are trying to achieve by using ND filters. I'm a pro still photographer and I'm new to video, but the physics of photography is the same in stills as in video.

    In still photos I would use a ND filter to control some part of the exposure that was not achievable by using the 3 variables to obtain the needed exposure for the effect I needed on a certain photo.

    On the p3 camera when you put a ND filter on it, which one of the 3 variables does it change? If it changes the iso then your video will have more grain, more noise. If it changes the FPS then it would slow it down which could cause problems with the video. If it changes the aperture then the other two would have to compensate for the change which could put more noise or more flicker in the video.

    So my question is why do you use the ND filters, what are you trying to achieve by using them?
     
  2. zezrum

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    You're right the physics of photography remain the same. When doing video, however, shutter speed is an essential ingredient in the final product. A faster shutter speed results in crisper, more video-like results, whereas a slower shutter speed creates some motion blur on each frame, resulting in a more cinematic result.

    In video, the rule of thumb is your shutter speed should be 2x the FPS you're shooting at in order to achieve a cinematic result. Thus, if you're shooting 30 frames per second, your shutter speed should be fixed at 60.

    The Phantom 3 camera is a fixed 2.8 aperture lens, which means that you have to do something to reduce the amount of light entering the lens if you don't want to over expose your video. You have two options: faster shutter speed, or a filter.

    ND filters allow you to keep your shutter speed slower, while limiting the amount of light entering the lens, so you can achieve good exposure without having to speed up your shutter.
     
  3. Cerone

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    Too fast of a shutter speed creates choppy and crisp video. You want it to be a little bit smoother/ blurred/ cinematic so shooting at 1/60 is ideal.
     
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  4. zezrum

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    One more thing - for photographers new to video there is another element that is important to consider, and that is FPS. Photogs are used to thinking of the exposure triangle with three ingredients: ISO, Shutter, and Aperture. Video introduces a 4th dimension of FPS, which is the # of frames per second that are captured at the specified shutter speed. FPS and shutter speed are two different things.

    Benefits of using a high shutter speed include the ability to pull crisp still photographs from the video. Benefits of using a slower shutter speed are smoother motion video.
     
  5. Garrie

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    How can you be a pro photographer when you don't even understand what the ND filter does? It's simple, a neutral density filter uniformly reduces the amount of light that reaches the sensor without affecting colour saturation. This helps you to use a slower shutter speed to get the same exposure as you would without a filter for that particular scene.

    You use ND filters in still photography too when you want to use a large aperture lens such as f2.8, f2.0, f1.8, f1.4, f1.2, or if you are very rich, f0.95(if you really are pro you would know which lens this is). Some cameras are limited by their maximum shutter speed, this means even at the fastest speed, the scene would still turn out over exposed. This is why you need the filter.

    The filter also helps in still photography when you want to blur moving objects such as a stream of water. ISO and Aperture can remain constant while your shutter speed can be slowed down.

    Carrying this technique into videography, the slowing down of shutter speed allows you to choose a suitable shutter speed which is approximated double that of your frame rate. This is crucial in videography to create a more natural looking video.

    I'm really surprised you even dare to say you are a pro photographer when you can't even just google the information. If I were you I would feel so embarrassed to even post that.
     
  6. Oso

    Oso

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    Garrie, that was a bit harsh. I'm surprised with your response this time, especially after the OP said he uses ND filters for stills, and @zezrum already did a terrific job explaining their use in video.
     
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  7. Garrie

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    It's harsh because somehow recently, a lot of people have been calling themselves pro photographers and asking questions that can be easily deduced.

    I started photography about 5 years ago, so far I've spent at least $22K getting pro gear and I work hard at my photography. I've done wedding shoots, birthdays shoots and general events.

    Even up till now, I shudder to even call myself a pro, because I know I still have so much more to learn. You can have all the pro gear in the world, you can have everyone saying your pictures are great, you may even feel that you have reached a level that is what a lay man might consider as pro, but would you dare to post a technical question without at least first googling the answer AND also stating that you are a "pro"?

    I wouldn't. And that is what makes me so angry.

    I got my p3 pro in August. I've got perhaps less than 10 days worth of flights so far. Still, I managed to find out about the 180° rule for videography, why we need to have ND filters, why we need to create blur instead of sharpness for video etc.

    It just irks me that someone comes in here and states that they are a pro and "don't know what you are trying to achieve by using ND filters "

    Perhaps my response was too curt and rude, if that is so, I do sincerely apologise.
     
  8. Chuck Young

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    @Garrie you should take it easy on or Still shooters. Stills and video are two different but related subjects. From the prospective of a still photographer, ND filters give you exposure in the proper f-stop range and depth of field. For video ND filters are used for exposure and shutter speed adjustments. @photodhill does not have the insight video presents, until now.

    Shutter speed is not adjustable on the P3, you get ~30 or ~60 and that is not enough to experience a change in shutter speed. 100 FPS would be what I would call the low end of "changing frame rates" 1000 FPS, now there is some slow motion for you. Strap one of those Phantom HD cameras in the link below on your Phantom 3 with a 50-2000mm telephoto lens, Now you have a freaking camera platform!

    High Speed Camera and Phantom Camera Products | Vision Research
     
  9. photodhill

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    Thanks everyone for your input on my question, I didn't realize there was a shutter speed with video I thought it was just frames per second as I said I'm new to video and I'm going to have to digest this part of video. I understand the aperture is fixed, so the only variables we have control of is shutter speed, FPS and ISO. From your answers then we have control of FPS and shutter speed, camera will not override that, so then the exposure is controlled by the ISO, so the camera then adjusts the ISO to adjust for the different lighting conditions, so that the camera maintains our FPS and shutter speed. Then you use the ND filter to maintain your FPS. I hope I said that correctly.

    To Garrie I don't appreciate your response, I stated in my original post that I would use ND filters to control exposure if I was trying to achieve a certain effect either depth of field or motion. Your response was totally uncalled for and you do not need to respond to posts in the manner you did
     
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  10. ianwood

    ianwood Taco Wrangler
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    I would agree. @Garrie, there is no need to take on this kind of attitude with people who don't have all the answers. The whole point of this forum is for people to be able ask questions and learn from each other. It is not to criticize the label that someone uses.
     
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  11. Garrie

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    Yeah I agree that I was wrong in the way I replied. It was a knee jerk reply to your query.

    I apologise.
     
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  12. zezrum

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    For the Phantom 3 video camera, FPS is tied to resolution. When you select your resolution you also are making a choice on FPS. THEN you can select your shutter speed from there. You use the ND filter to maintain your shutter speed & ISO as desired.

    In auto-mode/Program mode, the camera will adjust shutter and ISO as best it can to give you an even EV value (0). In manual mode you'll need to balance between ISO & shutter speed to get the desired EV. If you want a slower shutter, as is desired for more fluid & natural video, you'll have to use an ND filter to get there.

    In Colorado, on a cloudy day I use an ND16 to get a 0 to +.7 EV and keep a shutter of 60 at ISO 100.
     
  13. Vint

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    Pro photographers usually don't use ND filters because their cameras can stop down to F22 or so.
     
  14. Vint

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    Jeez....what do you use for a sunny day?
     
  15. B- Scene Films

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    My wife is a camera operator with about 25 years experience and about 18 of those as a member of the IATSE local. I asked her what the most common reason was for ND use in her business and she said to get the right T-stop. Generally, to open the lens up to achieve a specific aesthetic.

    I asked her about aerial. She stated "different ballgame" and re-iterated the previous comments about shutter speed control as the primary use. She stated that almost all aerials that she has done had the lens closed as far as possible (typically, not all of the way closed but, a stop or 2 before fully closed as it affects image quality) and focused at the hyperfocal distance. Her use of aerial is an actual helicopter, not a drone but it should still be about the same I would think.
     
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  16. Chuck Young

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    Not that I was a pro but I did use photographs to gather scientific data for a time. What you say is not necessarily true. I think a pro photographer would have a nice selection of ND filters to give specific results. Just simply tools of the trade. When I was using high speed photography one of the most important things was focus and focus depends on depth of field. At f/22 or above your depth of field is pretty much from zero to infinity. Pulling a good focus at f/22 is simply physically impossible. If you absolutely have to have super sharp focus I have found the best way is to set the f-stop as low as possible, like f/2, then begin to stack ND filters on the lens until you are able to get a really good focus. Remove the ND filter and set your f-stop for a good exposure. Typically If I was above f/5.6 I would use ND filters to back it down to f/5.6 for a satisfactory depth of field.

    Anytime your shutter speed is set for a significant fraction of the velocity of your subject you will begin to observe motion blur in both video and stills. Sometimes it is good and sometimes it is very bad. In video we typically want some motion blur to impart the artistic illusion of motion. Enter the ND filter to allow longer shutter speeds, typically 1/2 the frame rate. In stills sometimes you want to impart the illusion of motion such as a photo of a waterfall. Enter many ND filters and very long shutter speeds.

    The frame rate of the Phantom Pro is limited to between 24 and 60, really not what would be considered a variable to control exposure but does need attention for the above 1/2 rule. Likewise typically 24 fps is used to impart a cinematic -motion picture- quality to footage. For scientific purposes I would typically use around 1000 fps, sometimes as much as 150,000 fps, temporal resolution becomes very important sometimes.

    For the P3 Aperture is stuck at 2.8, aggravatingly.

    So essentially the aperture and frame rate are fixed so iso and shutter speed are the only two variables in this equation, enter the ND filter.


    iso=100-3200 (video) 100-1600 (photo)

    Shutter speed= 8s -1/8000s for stills and video except low shutter speed is a function of frame rate

    • 2.7K: 2704 x1520p 24/25/30 (29.97)
    • FHD: 1920x1080p 24/25/30/48/50/60
    • HD: 1280x720p 24/25/30/48/50/60

    So there you go, take that for what it is.
     
    #16 Chuck Young, Oct 5, 2015
    Last edited: Oct 5, 2015
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  17. Garrie

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    Not true and I have to stop you there. ND filters are needed especially when photographers want to achieve a shallow depth of field with a lens such as f1.2-2.8 in daylight. Due to the large aperture opening and bright daylight, the shutter speed sometimes isn't sufficiently fast enough to give you a "proper" exposure as determined by the camera's metering system, hence the picture will be overexposed.

    ND filters for photography isn't about reducing the amount of light per se, if that is so, then what's the point of having large aperture lenses if we are gonna shoot at f4-f22? It is specifically for such creative purposes such as taking a picture with shallow depth of field in broad daylight that ND filters are needed.
     
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  18. Garrie

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    Most modern prosumer dslrs can achieve shutter speeds of 1/8000s or even higher with E-shutter. But there are also many low end dslrs or mirrorless systems that have a maximum shutter speed of 1/4000.
    Sometimes a large aperture combined with the fastest shutter speed of 1/4000 may not be sufficient to achieve a proper exposure. Hence an ND filter is needed.

    Another reason an ND a filter is needed when using large aperture lenses is that some cameras use a leaf shutter mechanism. Even with the highest shutter speed(eg 1/4000s), the leaf shutter may not physically clear the circular field of view of the large aperture opening before the shot is taken. This means that a small part of the shutter mechanism is actually also captured in the frame. This is particularly apparent in the Fuji cameras. A slower shutter speed allows the leaf shutter mechanism to fully clear the frame.

    Www.dpreview.com/reviews/fujifilmx100/17
     
  19. dvarhol

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    This.
     
  20. witold

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    Good discussion. One thing that had me thinking recently is someone (respectable) saying that they prefer to add fake motion blur in Premiere/AE instead of relying on P3 camera motion blur, which they described as terrible.