Photography News | Issue 57 | photographynews.co.uk Technique 47 Camera School Here we lift the lid on all things camera related, showing how to get better results from your CSC or DSLR, and providing all the info you don’t find in the manual. So, stick with us and you’ll soon be wielding your camera like a pro. This month, why you need graduated ND filters and how to use them…
Words & pictures by Kingsley Singleton
Over the last few instalments of Camera School, we’ve looked at techniques which rely heavily on using neutral density (ND) filters; those which block a certain amount of light from entering the camera and therefore allow you to shoot at slower shutter speeds and/or wider apertures. These NDs are ‘full’, meaning that the amount of light filtration is constant across the frame, but there are also graduated ND filters. So what is the use of these and how are they best employed? Graduated NDs offer light filtration in a way that varies across the filter. One end of a graduated ND is clear, and therefore has no light blocking effect, while the other end is tinted to cut out light. How much darker the filter at the tinted end is depends on the strength you’re using, more on which below. The value of ND grads is balancing bright parts of a scenewith darker ones, and the typical example is when shooting landscapes. The sky might be much brighter than the foreground, and so in a single exposure one part of the picture will be too bright, or too dark– the camera can’t expose correctly for both at the same time. But with the graduated ND’s clear area over the darker part of the scene, and the tinted area over the lighter sky, a balance is made. It’s the same principle as wearing tinted sunglasses or the strip you used to find at the top of many car windscreens. How much filtration you need depends on the variation in the scene – the brighter one part is than another, the stronger a filter you’ll need. Below we look at choosing the right strength for the scene. WHEN DO YOU NEED GRADUATED ND FILTERS?
Images Get balanced exposures in scenes with a wide variation of light and dark with a graduated neutral density filter. With the clear part of the filter over the darkest part of the scene, your exposure will be spot on – all without having to fire up the computer.
ND grads are usually rectangular in shape, slotting into a filter holder on the front of the lens. As they’re longer than regular ‘full’ ND filters, they can be positioned so their effect can be precisely applied. You can get graduated ND filters in screw-in form, but these don’t allow any scope for positioning. WHAT ABOUT RAW? Many photographers choose to shoot in Raw file format, which does allow you to brighten or darken parts of a scene easily, and therefore some believe graduated NDs are redundant. You can also shoot separate frames for the bright part and the dark part of a scene, and blend the lighter and darker exposures in software. So are ND grads still needed? The answer comes in considering thedrawbacksofRawprocessingand exposure blending. With Raw you
are limited to the exposure latitude of the camera, and while modern cameras are very good, you can still lose quality if you need to darken by more than a couple of stops. Likewise, lightening dark parts of the frame can introduce noise artefacts. As for exposure blending, it takes additional time, can look unrealistic without sufficient skill, and, as the shutter speeds need to change for dark and light parts you may introduce unwanted motion in a subject, or the opposite, for instance losing blur in clouds. Combining frames may also introduce problems if a subject, such as a tree branch, has moved between exposures. Finally, while digital methods of filtration have their place, there’s little denying that the process of getting it right in-camera is far more satisfying than editing in software. In fact, the only time grads aren’t all that useful is when the skyline of a
picture is very broken, for example when a large building cuts up above the horizon. In those cases a gradwill darken that as well as the sky, so the image can look a bit unnatural. WHAT STRENGTH OF FILTER DO YOU NEED? The strength of graduated ND filter you need to balance the light in the scene is found by comparing the brightness of the light with the dark areas. For example, if the sky is one exposure stop brighter than the landscape, you’ll need a one-stop filter, also called ND2 or ND0.3. If it’s three stops brighter, you’ll need a three-stop filter, an ND8 or ND0.9. But how do you work out the relative brightness? There are several methods, but probably the simplest is this: put your camera in aperture- priority mode (A or Av), set it to the multi-segment (widest) metering mode, and then frame up on the
landscape portion of the scene. Make a mental note of the shutter speed provided by the camera’s metering. Let’s say it’s 1/4sec. Now repeat this process, composing so the frame is all sky. Read off the new shutter speed, let’s say it’s 1/30sec, and compare it to the first. From 1/4sec to 1/30sec is three exposure stops, so that’s the strength of filter you will need. And if you have only a one- and a two-stop filter, you can layer them to get the same effect as a three-stop version.
NEXTMONTH DO YOU NEED HARD OR SOFT GRADS? AND WHERE SHOULD YOU POSITION THEM IN THE FRAME?
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