ND filter is a very useful tool in the filmmaker's toolkit. Simply, as I encounter on the net, at that place are some issues and myths in what those filters are giving us. I've seen a bunch of times some weird pieces of communication, like you lot should use ND filter to avoid blown out dominicus or flicker in timelapse. So, from this post you'll learn and hopefully empathize how ND filters work and what they requite us.

This is very basic tutorial, for more than advance stuff you tin can check outShould you apply ND filters? Motion Blur in Timelapse.

What is an ND filter?

ND filter is a slice of drinking glass or plastic that you put in forepart of your lens to block some part of light that'south hitting the sensor. ND stands for Neutral Density, because the color of the filter should be neutral, I mean that information technology shouldn't modify any colors on your video, just exposure. I said shouldn't, because ND filters unremarkably cause some colour shifts, ordinarily green or magenta, sometimes blue. The cheaper the filter the stronger the tint.

There are different density filters. The table below shows some of them. The higher the ND number the more than lite it blocks. For more in depth description including dissimilar types of ND filters and this table explanation check out my post ND filters in Timelapse

The main misconception

ND filters change the exposure, so the brightness of the whole image. Sometimes people think that when they use the ND everything will continue the same exposure but for example they'll get darker sun that was previously blown out. That'south very far from true. ND can't modify the exposure of some role of the image and proceed untouched the other. That's but not how that filters work. When it comes to image brightness, using the ND gives yous exactly the same upshot that using shorter shutter speed or closing downwards the aperture (we're talking just nearly exposure, not motion blur or depth of field). So, if getting the shorter shutter speed doesn't aid the sun look better on your paradigm neither, does ND filter.

Of course there is something like gradual ND filters, that are used to darken just a role of the image, but they have quite limited usage in video. The darkened role of the filter is a square or of perpendicular shape. You can rotate it on the lens just there should always be a fairly straight line between the part which should be darkened and which shouldn't. It can be used for static camera shots. It's more than pop in photography, because of the camera movement limitations.

Why we employ NDs?

There are two basic reasons for using ND filters – to lengthen the shutter speed (for example we use NDs for that in timelapse) or to keep the aperture open (or both).

For the shutter speed – there is something like the 180 degrees rule in filmmaking, which says that you should use 1/2xfps to get a natural motion mistiness in your film. Then, for 25fps utilize shutter speed of 1/l s. Of course on a bright sunny twenty-four hour period information technology's hard to continue such shutter. At that place are three basic exposure parameters, so settings responsible for how brilliant your shot is. It'due south aperture, shutter speed and ISO. During daytime you keep your ISO low to avoid racket. Let's assume that you choose the aperture and you don't want to alter that. So you lot should adapt the shutter to the low-cal weather condition. However if you want to keep it according to the 180 degrees rule, you should add quaternary exposure parameter – ND filter. The stronger the filter is, the longer shutter you'll be able to set up.

Example

Allow's say you set all the exposure parameters equally described above and you get shutter speed of i/800 s. To keep it at 1/50s you should cake iv EV of light, so decrease the calorie-free hitting the sensor by 16 times – 2^4 (bank check out the table above to understand relationship between amount of blocked light and exposure values). To do that just employ the ND4 filter.

In timelapse we use lower fps values (when it comes to shooting, not displaying) and then according to 180 degrees rule we demand to get longer shutter speed. For example i second shutter speed for 2 seconds interval between pictures (so between each frame in concluding video). That's why nosotros use very strong ND filters.

NDs for drones

I feel like the near of the misconceptions come from drone pilots. ND filters for drones are popular, lots of people use them and not everyone knows why. The chief reason is to lengthen the shutter speed. We get a natural motility mistiness and then. Likewise, when shooting against the sun there are sometimes propellers shadows visible on the video when shot with the brusque shutter speed. Then too NDs are helpful.

Aperture

The 2d reason is the aperture. To get dainty cinematic shots we ordinarily want to go on the aperture open up, so low F value, similar F1.4, F2 etc. This gives us this lovely shallow depth of field – in other words we get this lovely background blur. If we have too much light in the scene we could shorten the shutter speed and keep the aperture open, but for the reasons described above we don't desire to exercise that. So, the easiest way is to utilize an ND filter.

Example

We take ISO100, shutter speed at desired 1/50 sec, but to continue the right exposure nosotros need to terminate downwardly the lens to F8. We would like to use F2 to blur the groundwork behind our subject. The departure between F2 and F5.six is 3 EV (F2 > F2.eight; F2.8 > F4; F4 > F5.half-dozen – each one is 1 EV), and so nosotros demand 6 times less low-cal. Nosotros only put the ND3 in front of our lens and suit the aperture.

Let'due south assume nosotros don't accept ND3, only ND4 (and we don't have any variable filter). Then we utilize ND4 and alter ISO for 200 or lengthen the shutter speed to 1/25. Usually ISO200 is very good quality and then of grade I would cull that.

Pretty much those are the reasons nosotros accept NDs in movie cameras like Sony FS5, Canon C100 etc. Thank you for reading the whole article 🙂 I hope you've learned something. Maybe you lot'll exist interested in watching my latest hyperlapse project, made just with a smartphone? 😉 >> Krakow Primary Foursquare – a Hyperlapse Walk + Making Of