Technology Tutorials

Using Neutral Density Filters

waves with a short exposure time

Neutral density (ND) filters scale back the quantity of sunshine getting into the digital camera, enabling a longer publicity time than in any other case potential. This will emphasize movement, or make an in any other case tumultuous scene seem surreal and quiescent. Alternatively, an ND filter additionally allows bigger apertures, which may produce a shallower depth of area, or obtain a sharper photograph. Both means, this can be a helpful and sometimes under-appreciated filter that deserves a deeper look. ND filters are additionally one of many best filters to make use of, and their impact can’t be replicated digitally — no less than not with a single shot.

Publicity time:
1/eight second at f/10 and ISO100

long exposure seascape with an ND filter

Publicity time: 30 seconds at f/10 and ISO100
Examples courtesy of kyle kruchok.

OVERVIEW

An ND filter is nothing greater than a semi-transparent piece of glass that will get positioned in entrance of your lens. What makes it particular, nevertheless, is that it obstructs a exactly managed fraction of incoming mild, and does so uniformly — thereby not altering picture distinction or sharpness. The obstruction additionally goals to be equal throughout the seen spectrum, thereby not introducing a colour forged (though this is not all the time the case). This final attribute additionally occurs to be why it is referred to as a impartial density filter.

ND filter

Instance of a screw-on ND filter.

Regardless that they could seem grey and even opaque to our eyes, this is not how your photograph will seem; the digital camera’s metering routinely compensates by letting in additional mild. Nevertheless, the viewfinder will nonetheless seem very darkish, so photographers typically compose their picture previous to putting the filter in entrance of the lens.

ND filters are specified by their light-reducing capability, the place stronger filters seem as darker shades of grey. Some widespread specs are summarized under:

Filter Power
(in f-stops)

Filter Terminology:

 

 


Mild Discount

Density

 


Widespread Makes use of


2

4X

zero.6 ND

Modest will increase in publicity time, comparable to with waterfalls.


Three

8X

zero.9 ND


10

~1,000X

Three.zero ND

Excessive will increase in publicity time,reminiscent of blurring in broad daylight.


13

~10,000X

Four.zero ND


20

~1,000,000X

6.zero ND


Notice: the sunshine discount elements above can be regarded as publicity time multipliers.

Many different intermediate strengths exist, however excessive precision sometimes is not wanted with ND filters. One can typically as an alternative regulate the aperture, ISO or shutter velocity by one cease with out considerably altering the picture.

Technical Word: Recall that every “stop” of light-reduction corresponds with a halving of sunshine. A given filter power subsequently passes just one/2strength of the preliminary incoming mild, the place “strength” is the filter power in stops. For instance, a Three-stop ND filter subsequently solely passes 1/eighth the incoming mild (since 1/23 = 1/(2*2*2) = 1/eight).

SHARPER & LONGER EXPOSURES

Neutral density filters can be utilized to create any mixture of (i) an extended publicity time, (ii) a shallower depth of area and (iii) a sharper photograph. Of those three, the primary is by far the most typical software, in order that’s the place we’ll begin.

long exposure waterfall with an ND filter


2 seconds

1/10 second


Columbia River Gorge, Oregon

Longer publicity occasions can obtain all kinds of inventive results, together with softening the looks of turbulent water, blurring waves of blowing grass, or emphasizing movement inside a crowd of individuals. For a full dialogue of those and different examples, see the tutorial on utilizing shutter velocity creatively.

Nevertheless, let’s concentrate on a selected waterfall instance. With no filter, one would use each the smallest aperture and the bottom ISO velocity out there. With a waterfall underneath smooth daylight, f/22 and ISO100 may yield an publicity of 1/10 second. Sadly, not solely is that this period inadequate, however the f-stop additionally needed to be elevated to the purpose of decreasing sharpness because of diffraction.

Using an ND filter permits you to tackle each of those issues, however the extent to which both is improved depends upon the way you select to allocate its impact. With a 5-stop ND filter, the identical settings would yield a 32X longer publicity time — giving the water a a lot silkier look. Alternatively, one may really feel that a 16X (Four-stop) publicity time improve is adequate when weighed towards the potential for having a sharper photograph, and will as an alternative additionally lower the f-stop to f/16.

How lengthy of an publicity does one sometimes want? For full impact, multi-second exposures are often a should. These can render clouds as streaks within the sky, blur shifting individuals past recognition, or make waves seem as a uniform, low-laying mist. Nevertheless, this is dependent upon the character of the movement, the quantity of topic magnification and the specified impact. The secret’s a lot of experimentation.

Throughout daylight, attaining this impact often requires having a 10-stop or higher ND filter power, which blocks all however a staggering 1/1000th of incoming mild. Attempt revisiting the publicity settings from a few of your previous pictures to see what ND filter strengths would’ve been wanted to realize multi-second exposures. For instance, if a given collection of landscapes used a 1/50 second shutter velocity at optimum aperture and ISO velocity, then these would’ve required a 10-stop ND filter to increase this publicity time to 20 seconds.

SHALLOWER DEPTH OF FIELD

Though ND filters are primarily used to realize longer exposures, a much less widespread software is to allow a shallower depth of area in very vibrant mild. For instance, most SLR cameras have a most shutter velocity of 1/4000 second, so a topic in direct daylight may subsequently require an f-stop larger than about f/Four.zero (at ISO100). With a 2-stop ND filter, one might scale back this to f/2.zero — yielding a dramatic enchancment in background blur and topic isolation.

example photo with a shallow depth of field in bright light

Photograph courtesy of alex campos. Word: above instance does not use an ND filter, however does illustrate a state of affairs the place one might probably assist (relying on the digital camera’s max shutter velocity).

However, these conditions are uncommon, and may often profit extra from photographing the topic underneath dimmer (and certain much less harsh) lighting. These conditions are additionally unlikely to require something stronger than a 2 or Three-stop ND filter.

DIGITAL NEUTRAL DENSITY FILTERS

Though ND filters can’t be replicated digitally, sure scenes and publicity occasions may be adequately emulated by using a way referred to as picture averaging. This works by combining a number of separate photographs in a means that simulates a single, longer publicity:

example of a digital neutral density filter technique


Select Photograph Averaging:

None

2X

4X

16X


Within the above instance, word how the water seems uncommon when solely two pictures have been averaged. Notice the looks of a double picture from the distant wave crest. This impact is much less pronounced with Four photographs, however hasn’t been eradicated totally.

complications with digital neutral density filters: discrete motion

Solar seems to make
discrete jumps throughout sky.

Typically, higher outcomes are achieved when (i) extra pictures are averaged, and (ii) the publicity time of every photograph is lengthy in comparison with the interval between them. The above instance required about 16 averaged photographs to adequately mimic an ND filter, partially as a result of every particular person publicity was so temporary.

Maybe the most important drawback with averaging is that shifting objects aren’t all the time rendered as steady streaks — regardless of what number of photographs are averaged. Pictures containing individuals, a visual solar, stars or different shifting objects are all notably prone.

OTHER TYPES & ALTERNATIVES

Filter Mounting Techniques. Since ND filters have the identical impact no matter how they’re shifted or rotated, utilizing a filter mounting system is not as important (in contrast to with GND filters). Nevertheless, these nonetheless have some benefits, together with faster insertion and removing, or liberating up a hand from holding the ND filter in place.

Step-Up & Step-Down Adaptors. These forestall you from having to buy a special screw-on filter measurement for every lens diameter (often listed as 77 mm, 72 mm, and so on.). One might then simply buy an ND filter that matches their largest lens, and use what’s referred to as a “step-up adaptor” to have this similar ND filer match on any smaller lenses.

Variable ND Filters & Stacking. With these, the power might be adjusted with out having to modify filters, however they’re additionally far more costly — typically much more so than a couple of separate filters. For extra flexibility on a price range, many photographers subsequently simply stack a number of ND filters when they should reproduce the light-reducing capacity of a single stronger (however unavailable) filter.

Substitutes. Typically different filter varieties can be utilized instead of an ND filter. Relying on the dimensions of your GND filters, these can typically be used as ND filters if the darker area is giant sufficient to cowl the complete lens. Alternatively, polarizing filters can perform as 2-Three cease ND filters, however provided that one additionally needs the polarized look, and solely when this filter is rotated for max impact. Some photographers do not buy 2 or Three-stop ND filters because of this, and as an alternative go for stronger varieties (similar to a 10-stops).

Filter Colour Casts. Some cheaper ND filters can introduce a colour forged. Fortunately this is not a serious drawback with digital cameras, since this could often be corrected by adjusting the photograph’s white stability in post-processing. Nevertheless, in excessive instances, cheaper filters can introduce shade casts which do not correlate with white stability settings — making shade forged removing rather more troublesome.

FURTHER READING

For comparable subjects, additionally go to the next tutorials: