How Do Nd Filters Work

WHAT IS A NEUTRAL DENSITY FILTER?

A neutral density filter (ND filter) is simply a filter that'south cuts the amount of light that enters your camera's lens. They are most usually used in mural photography when a photographer wants to create a longer exposures than what would normally be possible using only the camera's internal settings. In this article yous will learn how to utilise a neutral density filter and how to calculate long exposures.

Imagine that y'all want to crate a 30 second exposure in bright sunlight. Even with the camera set to ISO 100 with an aperture of f/22 the shutter speed will still be relatively fast. The only style to get a longer exposure in this situation is to place a neutral density filter in front of the lens.

TYPES OF NEUTRAL DENSITY FILTERS.

There are three types of ND filters. Solid ND, graduated ND, and variable ND. Graduated filters are useful when y'all only want to darken a portion of the image such as when the sky is brighter than the foreground. While these filters tin be quite useful, a whole article could be written about their awarding so I will save that for a future post.

Solid and variable ND filters darken the unabridged image which allows the photographer to blur annihilation that is moving. I highly recommend purchasing solid ND filters over variable ND filters since variable filter are often more trouble than what their worth. A variable filter allows you to change the density of the filter simply by turning information technology. Audio too practiced to be true? That'south because it is. Yous will spend a little more than money purchasing multiple solid ND filters but the quality of a solid neutral density filter will be much higher than a variable filter. Variable ND filters will frequently crusade artifacts on broad angle lenses and accept thick frames which can cause pretty terrible vignetting even without stacking filters.

Square VS. Circular ND FILTERS

When choosing a solid ND filter you can either choose a screw on filter or invest in a filter holder organization. If you're new to neutral density filters, yous may desire to start off with a screw on filter or two. In fact, I dearest my circular ND filters by Breakthrough Photography due to their natural color, ease of setup and low profile. A filter system can take a flake longer to setup and when the lighting is skillful I want to go the shot, non wrestle with my gear. Square filters too have more surface area which means more area for moisture to collect when shooting near the body of water, waterfalls, or in the rain. With that being said, good filter systems practice have their advantages. They let photographers to stack solid and graduated ND filters with footling to no vignetting. Again, I prefer Breakthrough Photography.

WHEN TO Utilize A NEUTRAL DENSITY FILTER.

Landscape photographers use ND filters when they want to create silky smooth water. This effect works wonderfully on waterfalls, creeks, lakes and oceans. Long exposures can as well be used to create dreamy streaks in a cloudy heaven and can even exist used to remove moving objects from a scene. If your shutter is long plenty and the objects are moving fast plenty, they volition not even show up in the shot!

Portrait photographers will sometimes apply low density ND filters when working with flashes. Since portrait photographers more often than not like to utilise a very shallow depth of field (open aperture), it may not exist desirable to end downwards the exposure using the aperture and if the ISO is already maxed out the next best choice is to apply a i or two stop neutral density filter.

HOW MANY STOPS SHOULD A NEUTRAL DENSITY FILTER Exist?

ND filters come in a broad variety of densities that are described in stops. A lite ND filter may only be 1 or two stops which is perfect for portrait photographers using a flash while a very dense ND might be 15 or twenty stops. And then how many stops should a ND filter exist? That depends on the amount of light that you're working with and the desired results that yous're going later.

For about practical landscape uses, iii, half-dozen and 10 stop filters are the most common. Three stop filters are smashing for when you need to button the exposure simply a piffling longer. I find three stop filters to be really useful on the far edges of twenty-four hour period when the calorie-free is already quite depression only the there's however too much light to create the length of exposure I'one thousand looking for.

Six cease filters are maybe the nearly flexible of the solid ND filters since they are night but not welding glass dark. Most modernistic cameras will yet be able to focus through a six stop ND filter in decent lighting conditions without a problem. If I were to pick just one neutral density filter to carry with me, it would exist a vi terminate filter.

X finish ND filters are very dark and are capable of achieving 30 second to two minute exposures in the eye of the day. These filters are useful for completely blurring moving water so it looks like a soft brume. 10 and fifteen stop filters are also very adept for removing moving objects from an image every bit if they were never there in the start identify.

Computing LONG EXPOSURES

When working with dense filters such every bit ten stop NDs information technology may exist necessary to summate the exposure manually because the light meter may non be able to give a proper reading through the dark glass. Luckily, calculating long exposures is not as difficult as it may seem. Any time the shutter speed is doubled or halved y'all adjust the exposure of the image past 1 cease. Similarly, the exposure is adjusted by one stop any fourth dimension yous double or halve the ISO.

For example, if I accept a photo at ISO 200, for one second I can get the exact same exposure by lowering the ISO to 100 and increasing the exposure time to two seconds while leaving the discontinuity where is was. In this example I took away one stop in the ISO only I also added a stop by doubling the exposure fourth dimension and then the shot is effectively the same exposure.

Computing aperture requires a lot more math than anyone in their correct mind is e'er going to do in the field. Luckily, information technology is yet very easy to calculate the aperture'south effect on exposure considering we know that all mod cameras operate in i/iii and one/2 finish increments. Nearly cameras will adjust exposure in one/3 increments past default but many can be programed to shoot in 1/2 stop increments also.

Cheque your camera'south carte to see if you lot're shooting in 1/three or 1/2 cease increments. Hint: If you take never changed the increase settings in your camera, yous're probably shooting in i/iii stop increments. If your camera is set to ane/three stop increments, adjusting the aperture dial past iii clicks volition adjust the exposure by one full stop. If you camera is set to 1/2 cease increments every two clicks will adjust the exposure by i cease.

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Real WORLD 10 STOP ND Case

Now let's look at a existent globe situation using a ten terminate ND filter. As mentioned above, your light meter might not be able to calculate the proper exposure due to the large amount of light that is beingness cutting by the filter. For this reason is is best to ready your camera'southward mode to manual. If there is a lot of light you might exist able to meter through the filter but if you're shooting on the edge of day you may have to calculate the exposure manually.

Then let's walk through how to shoot with a 10 stop ND filter in low lite. Kickoff we'll take a shot without the ND filter. For this instance allow's presume that our settings without a filter are ISO 100, f/xvi, i second.

After adding the ten cease filter we have to discover a way to add together ten stops of lite to our exposure. Nosotros can do this by adjusting the discontinuity, shutter speed, ISO or a combination of the three which is often the route that I terminate upwardly taking. If we're adding a ten stop filter, we're probably going after a very long exposure then we'll get-go off by adjusting our shutter speed.

Passing Day Over the Bay — v 1/ii minute long exposure

Remember that nosotros were shooting at ane second earlier we added the filter. To add one stop of light we'll suit the exposure from ane second to two seconds. At present we simply have nine more than stops to go! Nosotros tin can double the fourth dimension over again to 4 seconds and then double that to eight seconds which leaves us with seven more stops to go. Our exposure is still relatively brusk so let'southward double it again to sixteen and then to thirty seconds. Nosotros're one-half style at that place! (I know I shaved off two seconds but I'm going to assume that most people reading this are like me and non math wizards. Information technology'southward best to keep things every bit simple as possible when in the field.)

At this point we need to switch our camera to seedling fashion in oder to achieve an exposure over 30 seconds. Make sure to pay attention to the aperture settings when switching from transmission to bulb mode. The aperture is often ready independently betwixt manual and bulb modes. Afterwards making sure our aperture value remained at f16 nosotros tin program in our exposure using an intervalometer timer.

Annotation: If you do not take an intervalometer, you can use a regular cable release and spotter the stopwatch on your phone. Furthermore, many new cameras accept builtin intervalometers.

Let's proceed to double our exposure to ane minute, then to 2 minutes and finally to four minutes. We have gained viii stops of exposure only we nevertheless take 2 more to go. We could continue to double our exposure but nosotros'd terminate up at 16 minutes!!! Rather than shoot for xvi minutes, let's add a terminate by increasing the ISO course 100 to 200. Finally, let'due south add our final end by opening upwardly the aperture from f/xvi to f/11.

APPS FOR Computing EXPOSURES

If the above example has your head spinning, don't worry. There'south are many different apps that can be used to aid yous summate the proper exposure. LE Figurer is a gratis app that will calculate long exposures and even comes with a built in timer in case you do non have an intervalometer. PhotoPills is a paid app that has a long exposure calculator amid many other photography planning tools. It's a fantastic app and I highly recommend it for any mural photographer.

DEALING WITH LONG EXPOSURE NOISE

Long exposure times equate to added noise even at depression ISO settings. As long every bit your exposure does not exceeded 5 minutes, you should take relatively depression amounts of noise. Racket is created when the sensor heats upward during a long exposure. If information technology's cold outside, you may be able to get away with longer exposures before noticing much noise. Full frame cameras volition handle ultra long exposures better than crop sensor cameras. While shooting for longer than five minutes can add noise to a shot, sometimes the results can be worth the added noise. Experiment with unlike exposure times and see how they effect the image. If needed, yous can apply some noise reduction during post.

DEALING WITH CHANGING LIGHT

When shooting on the edge of day it's important to recollect that the earth moves faster than you lot think. The amount of light falling on a scene can alter dramatically in the affair of a few seconds, let alone a few minutes. Changing low-cal throws one more variable in our exposure equation that can be very hard to predict. When shooting during sunrise, you lot will demand to subtract a stop or two to recoup for the increment in light that will happen as the sun continues to add calorie-free to the scene throughout the exposure. The opposite of this is truthful at sunset. During sunset you will accept to add a stop or two in order to recoup for the fading light.

ISO and aperture tin can sometimes exist more effective at controlling exposure when the light is rapidly irresolute considering they do not add or subtract any time to the exposure. Imagine that the lord's day is setting and your exposure is already 5 minutes. If you add together a finish of light using the shutter, your shot will then be x minutes long. The corporeality of light that disappears in those added 5 minutes volition more than like be greater than the end that you lot added. Therefore, a better choice might be to boost the ISO or open upward the aperture.

Fifty-fifty during the middle of the twenty-four hour period, moving clouds can cause each long exposure shot to look quite different. It's a good idea to try multiple shots if there are a lot of clouds in the heaven. The difference a few minutes makes tin be amazing.

I will often have a few shots without a filter if the light is looking skilful. This way I tin alloy the shots if the lite changes or at the very least I have a few solid exposures that were taken with a fast shutter.

WATCH OUT FOR UNWANTED MOVEMENT.

Pay shut attention to elements within the scene that could cause unwanted movement blur. Tree branches and plants rarely stay still for very long. Sometimes the blurry edges of plants can be an interesting look. Other times yous may want the vegetation to stay still. If your exposure is just a few seconds long you may be able to fourth dimension your exposure and then it happens when the wind is not blowing. If you are attempting a very long exposure in that location might not exist much you tin do other than embrace the soft edges from the wind. Photographers who take stiff Photoshop skills might exist able to blended an image using 1 fast shot that was taken without the ND filter and 1 that was taken with the ND filter. This technique can show to be quite tedious though so I will non cover it in this commodity.

DON'T LET LIGHT LEAKS RUIN YOUR SHOTS

Light is a lensman'due south best friend but information technology can too exist our worst enemy. Light leaks will surely ruin a practiced long exposure. The telltale sign of a lite leak is a magenta cast that appears in only a portion of the image. It is always a good idea for DSLR shooters to encompass the photographic camera'south centre piece specially if the dominicus is backside the camera. If yous fail to cover the eyepiece, light can enter the camera from the rear and cause a terrible color cast.

High endNikon DSLR'due south accept a a convenient eyepiece curtain that should exist used whenever performing long exposures. If your camera does not have a built in eyepiece embrace you may desire to bear some gaffers record that can be used to temporarily block low-cal while you are performing a long exposure. Mirrorless shooters practice not take to worry about rear calorie-free leaks since there are the view finder is electronic.

Light leaks can likewise occur when using filter folders. Sometime light will creep into the filter and bounce effectually during the shot. For this reason, I prefer screw on filters in well-nigh cases. If you lot discover a lite leak when using a filter system, try to use gaffers tape to cease the leak.

NEUTRAL DENSITY FILTERS AND Color Cast PROBLEMS

Most ND filters accept at a petty bit of a color bandage. Some are worse than others. Breakthrough Filters tend to exist the most colour neutral filters that I take institute and they are backed by a twenty year warranty.

Night POLARIZER FILTERS

In recent years, filter companies have started to make dark PL filters. A dark PL is a combination of a neutral density filter and polarizer all in 1. While most all in one products are terrible, night PL filters work amazingly well! They come up in various densities and remove of the need to stack a ND and PL filter together which reduces the chance of vignetting at wider focal lengths.

Determination

Neutral Density filters are a great way to add together atmosphere to a shot with moving elements. I recommend experimenting with various density filters and exposure times to gain a greater understand of how ND filters work. Notice the differences in a half second exposure and a 2 2nd exposure. And so compare those results with a xxx second exposure and a five minute exposure. Practise gauging exposures under changing lighting weather and see if y'all tin accurately predict the correct exposure. Picket your histogram and try to bring information technology to the correct side of the graph.

Happy shooting!