tips - optical filters

8/10/2019 Tips - Optical Filters

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Back in the days of film, youd have

to use optical filters for a variety of

reasons. In addition to protecting a

lens against the elements and providingsome protection against knocks, filters

were used to correct the colour balance of

film for example to add a warm orange tint

or a cool blue one to record a neutral result

under different lighting, depending on the

film stock you were using. Digital cameras

dont need this type of filtration, as their

white balance control enables you to

neutralise any colour cast on the fly.

In the days before Photoshop, youd

often have to resort to using filters to

achieve certain effects in-camera too, such

as a soft focus filter to add a hazy look or a

graduated tobacco filter to artificially boost

a sunset. These days theres no need to try

and achieve an effect like this in-camera;

you can do it all post-shoot using digital

filters, adjustment layers and other tools.

So, the only reason you still need to fit

You can go some way towards reproducing

the latter effect in Photoshop, but as for

reducing glare and removing reflections

well, itll take hours of painstaking work,

if you can reproduce the effect at all.

There are some downsides to using

a polarising filter. For a start, theyre not

cheap. In fact, a polariser will certainly be the

Is there any po nt n us ngoptical filters on lenses?Learn why theres stilla place for lens filtersin your camera bag

Youcanreplicatetheeffectsof

polarisersandNDgradfiltersin

Photoshopbutyoullneedan

NDfilte

rforextendingexposurestocreatesilkyskiesan

dseas!


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A polariser willcertainly be themost expensive filter

you buy, this side ofa LEE Big Stopper

Real vs fake:Graduated ND filtersWhy ND grad?Without an ND grad, the contrast between

the landscape and the sky may be too great

for the camera to record detail in both areas

in a single exposure. Expose for the land, and

the sky may be overexposed and featureless;

take a shot with the sky exposed correctly

and the landscape may be underexposed.

A neutral density graduated

filter enables you to record

detail in both a bright sky

and a darker foreground.Position the clear part of

the filter over the land and

the darker part over the sky,

and you bring the exposure

of the two areas closertogether, within the

dynamic range of the

cameras sensor. Arguably,

these days theres less of a

need for these filters, as you

can tackle exposuredifferences when you

process your images. If the

exposure difference

is relatively small, you can

darken the sky or lighten

the landscape with an

adjustment layer, and

then mask the effect as

required. If the exposuredifference is more extreme,

then shooting two or more

bracketed exposures with

a tripod-mounted camera

will enable you to blend

the images to capture an

expanded brightness range.

REALNDGRAD

FAKENDGRAD

Sky appears too bright

Land exposed correctly

Sky exposed correctly

Land appears too dark

biggest lens diameter you own, and use

step-up rings to fit it to your smaller lenses.

Polarisers also cut the amount of light

entering the lens, by approximately two

stops when fully polarised. This can lead to

slower shutter speeds, increasing the risk of

motion blur or camera shake; one way to

compensate for this is to increase the ISO.If youwantto capture the effects of

motion blur, a standard ND filter is often the

way to go in bright conditions. These are

a solid neutral grey, and are used to simply

cut the amount of light entering the lens.

Theyre available in a range of strengths,

each rated for the number of stops or

exposure values they reduce the light by.

So a three-stop ND (sometimes called a 0.9

ND or an ND8) enables you to reduce theshutter speed by three stops; for example,

you could use a shutter speed of 1/15 sec


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Its relatively straightforward to emulate the effects

of ND grads in Photoshop, Elements or Lightroom,

but doing the same for a polarising filter is more

challenging. To boost the contrast between a blue

sky and white clouds in a similar way to a polariser,

shoot in Raw and process your files in Lightroom/

Photoshop ACR. Select the Blue slider under the

Lightness tab of the HSL panel, and drag it left to

darken the sky. The giveaway that a polariser hasnt

been used is the reflections in the windows; theyrestill present in the digital fake. Recreating the effect

of an ND filter on moving clouds is easier: select the

sky in Photoshop, then apply the Motion Blur filter.

Real vs fake: NDfilters & polarisers

Digital filterdrawbacksAlthough you can resolve exposure

issues and recreate the effects of some

filters in software, doing it digitally brings

its own problems. For a start, you can

only work with what youve recorded.

If the highlights in the sky were severely

overexposed at the point of capture,

you wont be able to bring them back

with a digital grad. As you can see in

th i b l t f d k

While using filters at the time of shooting

can mean less time spent in front of the

computer, and is arguably more enjoyable,

you will face a few problems. If you attach

a filter to an ultra-wide angle lens, you may

see it in the corners of your shots; this

problem is exacerbated on full-frame

cameras, or if you stack more than onefilter, and youll have to either zoom in a

little, crop the shot or choose thinner

filters. If youre not careful when you

Optical filter pitfalls

REALPOLARISINGFILTER FAKEPOLARISI

NGFILTER

Fit a thick polariser to a 17mm lens on a

full-frame 5D and this is what youll see!


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to exaggerate movement where youd

normally use 1/125 sec. Faking a long

exposure effect in Photoshop wontalways look as natural as the real thing.

Its fairly easy to select the sky and apply

a blur filter to clouds, but adding motion

blur effects to water, foliage and other

objects is slightly trickier.

If you want to balance the exposure of

a landscape and bright sky, tradition has it

that youd reach for a graduated ND filter.

However, you can achieve the same effect

by capturing one exposure for the sky and

another for the landscape, and blending

them with layer masks or HDR software.

This option is useful when areas of the

scene would cross the boundary wherethe dark and clear parts of the filter meet,

such as in cityscapes or a coastline with

cliffs; if you used an ND grad youd darken

parts of the landscape, as well as the sky.

That aside, theres a lot to be said for

getting it right in-camera. Spending a few

more minutes fitting filters and working

out exposure settings may save you time

at the editing stage and the satisfaction

that comes from doing it hands-on

shouldnt be overlooked either!

Xxxxx

Colour castsSome optical filters can create a colour

cast, leaving images looking a little pink

or too warm. To counter this, you could

try using your cameras White Balance

Correction option in the red shooting

menu to tweak the amount of blue,

amber, green and magenta; however,

wed recommend shooting Raw so that

you can do this when you process the

image. Strong ND filters can leave images

with a heavy blue cast, so dial in a Kelvin

white balance value of 7000K or more.

REAL10-STOPNDFILTER

FAKENDFILTER

UNCORRECTED10-STOPNDFILTER

CORRECTED10-STOPNDFILTER

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