滤镜原理

滤镜原理

Taking good photographs isn’t just about framing your subject and learning composition. Learning how to control how much light enters your camera and for how long can help you take photos that elude the average photographer. Neutral density filters are a powerful tool towards that end. Here’s what they are and how to use them.

拍摄好照片不只是构图和学习构图 。 了解如何控制有多少光进入相机以及多长时间可以帮助您拍摄普通摄影师无法拍摄的照片。 中性密度过滤器是实现此目标的强大工具。 它们是什么以及如何使用它们。

Neutral density filters (or ND filters) reduce the overall intensity of the light that passes through them, without affecting the color of that light. When you place an ND filter like these over the lens of a DSLR camera, it allows less light to pass through, which gives you the flexibility to open the aperture wider or expose a photo for longer than you would be able to otherwise.

中性密度滤镜(或ND滤镜)可降低通过它们的光的总强度，而不会影响该光的颜色。 当您将此类 ND滤镜放置在DSLR相机的镜头上时，它会通过较少的光，这使您可以灵活地打开更大的光圈或使照片曝光更长的时间。

To understand why this is helpful, we need to look a bit at how a camera works. When you take a picture with your camera, the aperture opens to allow light to hit your camera’s sensor. On more advanced cameras like DSLRs, you can adjust two key elements of that process: the size of the aperture (measured in f-stops), and the shutter speed, which determines how long the aperture is opened. These two numbers combined determine how much light hits your camera’s sensor.

要了解为什么这样做有帮助，我们需要看一下相机的工作原理。 用相机拍摄照片时， 光圈会打开，以允许光线照射相机的传感器。 在像数码单反相机这样的更高级的相机上，您可以调整该过程的两个关键要素：光圈的大小( 以f级为单位 )，以及确定光圈打开多长时间的快门速度 。 这两个数字的总和决定了有多少光照射到相机的传感器上。

This information is important for a ton of common photography tasks. If you want to photograph a sports game, for example, you’ll need to use a fast shutter speed in order to reduce motion blur. If you take pictures at night, you’ll either need a wider aperture in order to let in more light, or a slower shutter speed (and a tripod) to catch enough light for a well-lit picture. You can even do cool things like use an extra-long exposure to take pictures of fireworks.

此信息对于许多常见的摄影任务很重要。 例如，如果您想拍摄体育比赛，则需要使用快速快门速度以减少运动模糊 。 如果您在晚上拍摄照片，则可能需要更大的光圈以让更多的光线进入，或者需要较低的快门速度(和三脚架)来捕捉足够的光线以拍摄出光线充足的照片。 您甚至可以做一些很酷的事情，例如使用超长时间曝光拍摄焰火照片 。

Neutral density filters give you more flexibility to play with these settings. For example, a long outdoor exposure with a wide aperture at night may look good, but if you used those same settings during the day, your photos will be a blown out, overexposed mess. With an ND filter, however, you can filter all the daylight coming into your camera and still use a long exposure to get the effect you want without ruining your photo.

中性密度滤镜使您可以更灵活地使用这些设置。 例如，夜晚长时间在户外进行大光圈曝光可能看起来不错，但是如果您在白天使用相同的设置，则照片会显得过分曝光，混乱。 但是，使用ND滤镜时，您可以滤除进入相机的所有日光，并且仍然长时间曝光以获得想要的效果，而不会破坏照片。

For example, consider the above image, comprised of two similar photos from Wikimedia. The left side of this photo was taken with an exposure of 1/30th of a second and no filter. The right side, however, was shot with an ND1000 filter, which allows only .1% of light through it. That photo was taken with a 57 second exposure. Yes, that means the shutter was open for nearly a full minute. Despite the much longer exposure time, the filtered photograph on the right still looks relatively normal. The only change is that the surface of the water (which would’ve been in constant motion while the shutter was open) now has a silky smooth look. You can frequently see this effect used to create dazzling images of waterfalls, oceans, and other scenery where one element of a scene moves but the rest of the shot stays stationary.

例如，考虑上图，其中包含Wikimedia的两张相似照片 。 这张照片的左侧是在1/30秒的曝光下拍摄的，并且没有滤镜。 但是，右侧是使用ND1000滤镜拍摄的， 该滤镜仅允许0.1％的光通过。 那张照片是用57秒的曝光拍摄的。 是的，这意味着快门已打开近一分钟。 尽管曝光时间更长，但右侧经过过滤的照片看起来仍然相对正常。 唯一的变化是水表面(在百叶窗打开时本来会不断运动)现在具有丝般柔滑的外观。 您经常会看到这种效果，用于创建瀑布，海洋和其他风景的令人眼花images乱的图像，其中场景的一个元素移动了，而其余镜头则保持静止。

You can also use ND filters to selectively control the light in a scene. Graduated ND filters feature clear glass on one side of the filter, a full ND filter on the other side, and a small gradient in between. This is helpful if you want to take a picture of a scene where one half of the image (say, the sky) is very bright, but the other half (say, the ground) is darker. Place the darker half of the graduated ND filter over the sky, and the light entering your camera will be more even. You can expose for the ground without blowing out the sky.

您还可以使用ND滤镜选择性地控制场景中的光线。 带刻度的ND滤镜的一侧为透明玻璃，另一侧为全ND滤镜，且两者之间的梯度很小。 如果您想拍摄一个场景，其中图像的一半(例如，天空)非常明亮，而另一半(例如，地面)则更暗，这将很有帮助。 将渐变色ND滤镜的较暗一半放在天空上，进入相机的光线将更均匀。 您可以暴露在地面而不会炸毁天空。

Tricks like this are common in the world of film, as well. Whenever you see a scene with people in front of a window, chances are good that the window is layered with an ND filter gel that reduces the light shining through. If you were on set, the windows would look dim, since your eyes do a better job of distinguishing between the darker room and brighter outdoors. However, when you shoot the room through a camera, that ND gel makes the window look a lot better. Most of the time, photographers won’t need to ND gel a window, but it’s important to be aware of the light sources in your set up and pay attention to how to properly filter them to make the lighting in your scene even.

这样的技巧在电影界也很普遍。 每当您看到窗前有人的场景时，窗户上都可以放置一层ND滤镜凝胶 ，以减少光线直射的机会。 如果您在现场，窗户会显得暗淡，因为您的眼睛可以更好地区分较暗的房间和较亮的户外。 但是，当您通过相机拍摄房间时， ND凝胶使窗户看起来好很多 。 在大多数情况下，摄影师不需要ND凝胶窗口，但重要的是要注意设置中的光源，并注意如何正确过滤它们以使场景中的照明均匀。

Above: Fountain shot at f/6.3 and 1/200 second exposure. Below: f/6.3 and 0.4 seconds (or 80x longer) with ND16 filter. Note: some color correction was done to the second photo to fix a color cast from the ND filter.

上图：喷泉以f / 6.3和1/200秒曝光拍摄。 下图：使用ND16滤镜的f / 6.3和0.4秒(或更长的80倍)。 注意：对第二张照片进行了一些色彩校正，以固定ND滤镜的偏色。

To get started with ND filters, you’ll need to know the notation used to rate them. While ND filters use several confusing notations, the most common is the ND number, often written as ND2, ND4, ND8, and so on. You can think of the number in this notation as the bottom of a fraction. An ND2 filter allows 1/2 of all light through it. An ND4 filter allows 1/4th of all light through it. An ND8 filter allows 1/8th of all light to pass through, and so on.

要开始使用ND滤镜，您需要知道用来对它们进行评级的符号。 尽管ND过滤器使用了几种令人困惑的符号 ，但最常见的是ND号，通常写为ND2，ND4，ND8等。 您可以将这种表示法中的数字视为分数的底部。 ND2滤镜允许所有光的1/2通过。 ND4滤光片允许所有光的1/4透过。 ND8滤光片允许所有光的1/8穿过，依此类推。

You might notice the numbers for these ND filter ratings double with each new filter. With a few exceptions, most ND filters you find will be a successive power of two. The reason for this is every time you halve the amount of light that passes through a filter, you effectively reduce the light entering your camera by one whole f-stop. So, an ND2 filter reduces the light by one f-stop. An ND4 filter reduces it by two f-stops, and on and on.

您可能会注意到，对于每个新滤镜，这些ND滤镜等级的数字都会翻倍。 除少数例外，您发现的大多数ND滤镜都是连续的2的幂。 这样做的原因是，每当您使通过滤镜的光量减半时，就可以将整个进入相机的光有效地减少整个f级。 因此，ND2滤镜可减少一个f级光。 ND4滤镜可通过两个f-stop来不断降低它。

This is a handy shorthand when you’re calculating your light needs for a shot. Say you’re taking a photo of a waterfall and you want that silky smooth look for the water. You take a normal shot with an f-stop of f/22—this very small aperture ensures the entire scene is in focus—using Aperture Priority mode on your camera. At this setting, say your shutter speed for a properly exposed photo would be one second (to make the math easy for now).

当您计算拍摄的光线需求时，这是一个方便的简写。 假设您要拍摄瀑布的照片，并且想要水般柔滑的外观。 使用相机的Aperture Priority模式，可以以f / 22的光圈值进行正常拍摄-这个很小的光圈可确保整个场景清晰对焦。 在此设置下，假设一张正确曝光的照片的快门速度将为一秒钟(现在使计算变得容易)。

Anything longer than one second and your photo would be blown out and too bright. So, you place an ND16 filter and an ND4 filter over your camera. This effectively reduces the light by six total stops. So, to compensate with your shutter speed, you’ll need to double the length of your exposure six times. A one second exposure, doubled six times (1 * 2 * 2 * 2 * 2 * 2 * 2) comes out to 64 seconds. You’re gonna need Bulb Mode for this one, but now you’ve calculated your proper exposure time.

超过一秒钟的时间，您的照片将被炸毁并且太亮。 因此，将ND16滤镜和ND4滤镜放在相机上。 这有效地减少了总共六个光阑的光线。 因此，为了补偿快门速度，您需要将曝光时间加倍六倍。 一秒钟的曝光时间翻了六倍(1 * 2 * 2 * 2 * 2 * 2 * 2)，达到64秒。 您将需要为此使用“灯泡模式” ，但是现在您已经计算出适当的曝光时间。

You can also use this shorthand for taking basic landscape photography. Often, the sky is brighter than the ground, so to take a good picture of both, you want the sky and the ground to be within about one f-stop of each other. So, for example, if your sky is properly exposed at f/16, while the ground is properly exposed at f/5.6, then they are three full stops apart from each other. But you now know you can position a graduated ND4 filter (which reduces light by two stops) over the sky to bring the light closer together. Now you can take a picture of the landscape without blowing out or under exposing half the frame.

您也可以使用此速记进行基本的风景摄影。 通常，天空比地面明亮，因此要同时拍摄两者，您需要将天空和地面保持在大约一个f级之间。 因此，例如，如果您的天空以f / 16正确暴露，而地面以f / 5.6正确暴露，则它们彼此相距三个句点。 但是现在您知道您可以在天空上放置一个带刻度的ND4滤镜(将光线减少两个档次)，以使光线更靠近。 现在，您可以拍摄风景照片，而不会吹大或曝光不足一半。

ND filters give you a whole new degree of flexibility that you can’t always get by adjusting your aperture or shutter speed alone. They’re also relatively cheap. This kit is the one I used for the photos of the fountain above. It costs less than $30, comes with ND2-ND16, and a variety of adapter rings for your DSLR camera. While the glass isn’t perfect (you may need to do some color correction later), it’s a handy tool to have in your bag.

ND滤镜为您提供了全新的灵活性，而您仅通过调整光圈或快门速度就无法获得这种灵活性。 它们也相对便宜。 这个工具包是我用来拍摄上方喷泉照片的工具包 。 它的价格不到30美元，带有ND2-ND16，以及适用于您的DSLR相机的各种转接环。 虽然玻璃杯不是完美的(以后可能需要进行一些颜色校正)，但是这是装在袋子中的便捷工具。

翻译自: https://www.howtogeek.com/325803/how-neutral-density-filters-work-and-how-to-use-them-for-better-photography/

滤镜原理