get to grips with landscape filters

The Filter Trial The charge: Camera filters are redundant in the digital age. The case for the prosecution: Why spend thousands on expensive lenses only to put cheap resin in front of them when the same effects can all now be achieved in postproduction using software filters? The case for the defence: Exposure merging and post-production techniques are not always an option and are no substitute for getting it right in-camera, while certain effects cannot be replicated in the digital darkroom. The best bit of advice I ever heard regarding the use of filters came from my first year lecturer at photography college, in the early 1980s. He told us,  If youthinking of using filters; don.  He and our Council for the Prosecution were right; why put anything in front of our pricey glass that we didn t need to? The trouble was, back then, we often needed to use filters for colour balancing and aesthetic reasons, or so we thought. The height of 1980s creativity demanded heavy warming filters with a touch of diffusion and a tobacco grad thrown in. Every era has its gruesome abominations —the 1990s saw cross-processing, now we have HDR-but the whole photographic world has shifted on its axis, and coloured and special effect filters have now become redundant. Even if we did want to recreate such a retro look, we can do it now with so much more control in post-production; changing the colour balance of an image at the Raw conversion stage is as easy as putting the bins out. There is simply no reason to be using coloured filters of any description. Other filters live on, though; many of which I believe are indispensable tools. get to grips with landscape filtersWHY USE FILTERS? Filters modify the image-forming light before it reaches the sensor, and no amount of clever techniques in the digital darkroom can truly replicate that. If the highlight detail in the sky is blown, no digital darkroom wizardry will ever be able to retrieve it. Exposure merging is a technique that is very handy to master, but not an option when working handheld or shooting subjects incorporating movement. The effect of polarisers is similarly impossible to replicate digitally, although some do attempt this by manipulating contrast. Fiddling with precious pixels is, however, never a substitute for getting it right in-camera. And slowing down exposures to convey motion is a technique most of us occasionally revel in, and that usually demands the use of filters. Until the manufacturers finally understand our true needs and start designing cameras with extremely low, as well as sky high, ISO capabilities, we ll still need to put dark bits of glass in front of our lenses to really show the movement of the barley blowing in the breeze or the waves lapping on the beach. In a nutshell, there are convincing arguments for the defence but, above all, it comes down to an attitude; getting it right in-camera is a good photographic discipline. I would far prefer to be out getting my boots muddy chasing the light rather than sat there slaving over manipulations in front of a glowing monitor. TYPES OF FILTER ND GRADS A neutral density graduated filter (ND grad) is dark at the top, clear at the bottom, and typically used to balance the exposure between the land and the sky. This remains the case, but the way I use them has changed. The number (0.9, for example) refers to the density of the darkest bit; 0.3 density is the equivalent of 1-stop, so 0.9 ND grad has a 3-stop exposure differential between top and bottom. Whatreally important when choosing a filter is the colour fidelity of the dark bit; the density should be truly neutral, with no gruesome colour cast. Such casts affecting all of the image area can be easily corrected at the Raw conversion stage, but when that cast is applied to only a selective part of the image, such as the sky, it s a real pain. Truly neutral filters are not easy to make; hence the higher price. The hard or soft terminology refers to the severity of the gradation; soft has a gradual transition from clear to dark, hard is more pronounced. ND FILTERS Straight neutral density filters are just dark bits of glass designed to retard exposures. A 0.9 (3-stop) ND is a good general purpose filter handy for slowing the world down. What s key with all filters is the optically quality. A poor quality filter can cause flare, rob a lens of its precious performance, and introduce colour fringing. A warning: the really dense filters, like B+W s 10x ND and Lee Filters  Big Stopper, are never truly neutral; in fact every one is different. The demands of making glass so dense dictate that it should be so, but that s not an insurmountable problem. As the cast is uniform, removing it in postproduction is easy. It just involves doing tests with white cards. POLARISERS It s a transformation that cannot be replicated in post-production. There are two types of polarising filter: linear and circular. Unfortunately for digital cameras we need the pricier circular type. POST-PRODUCTION FILTERS Embedded within the tools available to us in our editing software is a range of post-production filters. Lightroom, for example, has a very handy graduated filter tool plus all sorts of presets for certain looks and black & white work. These are simply a combination of colour balance and channel mixing adjustments that are handy to try, but the grad filter tool is altogether more useful. A graduated tone of any colour and density can be added as and where required. It s worth remembering though that highlights that have been lost in overexposure can never be retrieved, and this tool is only introducing tone, not detail. WHEN TO USE A FILTER GRADUATED FILTERS Graduated filters are essentially contrast control devices. By holding back the exposure on the sky they enable us to expose properly for the landscape below; thus maximising the shadow detail under the rocks while retaining every detail in the billowing clouds. Landscape scenes are often made by the drama of the sky at dawn and dusk, and when the contrast between the heavens and earth is too much for the camera to handle, a grad is a must. The other option is to take two or more exposures to be merged later in Photoshop; one for the sky and one for the landscape. It s a straightforward technique that I use often; camera filters and exposure merging are not two mutually exclusive working methods. In fact, I ll sometimes use both in a very high contrast situation, such as shooting straight towards the sun rising over the mountains; the grad in this case is keeping the exposure differential at manageable levels, thus easing obtaining a natural look to the composite image. POLARISING FILTERS Polarising filters work most effectively when the lens axis is perpendicular to the angle of light. With direct early morning sunlight illuminating a landscape from the east, a direction of view to the north or south reveals the texture, form and shape of the landscape. A sidelit scene is also when a polariser works best; colours in vegetation are saturated, haze is reduced and the blue in the sky becomes deeper as the filter is rotated on the lens. Polarisers work best in strong directional sunlight; their effect on a grey day is barely discernible, unless you ve gone for a walk in the damp woods. If you ever find yourself hiking through a cloud forest, remember to pack a polariser. Moist green vegetation looks even more soggily saturated when a polariser filter is deployed. Remember though, down on the dark forest floor the additional 2-stop exposure factor does prolong exposures interminably; don t even think about leaving the tripod behind. As tempting as it is to use a polariser in only its fully on position, the best images shot with them are achieved by using a subtle setting somewhere between the fully on and the off position. The more you use it, the better you will become at judging the degree of polarisation required for any given scene. ND FILTERS Straight NDs are used when motion needs to be conveyed. Images of swaying vegetation and scudding clouds became synonymous with the large film format; now, to achieve minutes long exposures, we need some seriously dense filters. Try explaining to a layman why we spend thousands on expensive cameras and lenses only to put a piece of glass so dark we can t even see through it in front; itmadness, but our only option. There are motion blur filters in Photoshop, but you canbeat the look of Mother Nature s random hand when using ND filters. PRO TIP If you are having trouble seeing the effect of a ND grad filter on your composition as you slide it up and down in the holder, then try stopping the lens aperture down by using the depth of field preview button on your camera. With that pressed, you should be able to work out exactly where the ND grad divide is lying in your image. It is far easier to see this when you are using small apertures, such as f/16 or f/22. get to grips with landscape filtersCHOOSING THE RIGHT FILTER So, how do you determine which filter to use? Remember; don t use any unless you have to, but if yousuffering white sky syndrome a ND grad is a must. In theory, taking exposure readings from both the sky and landscape, determining the exposure difference between the two, then reaching for the appropriate grad is the way to go. If the sky is two stops brighter than the fields a 0.6 ND grad is the one for the job. In practice, I find experience is a more reliable ally to call on when deciding which grad to use, but there s no shame in sucking and seeing. Using Live View or doing a test shot to judge the effect of the grad is a fail-safe method. Be wary of being too heavy handed; an over-darkened sky may look funky on Top Gear but not in your carefully crafted masterpieces. A sky that is bright but with all the necessary detail recorded is preferable to a sky that is too dark; the former can be easily darkened, but lightening an ominous black sky is fraught with pitfalls. DECIDING ON DENSITY Deciding if a straight ND is needed and what density to use will be determined by just how much movement you wish to convey. For slightly blurring breaking waves and gently swaying trees, a 0.9 will do the job, particularly in the soft light of Hour’. For really prolonging exposures beyond the 30 second mark, a 10x ND will be required. Waiting for a shot to  cook  as the world moves in front of the lens is fun, although the novelty of hanging around by the tripod as a 12-minute exposure ticks past does soon wear thin. TO POLARISE OR NOT TO POLARISE The easiest way to assess whether to use a polariser is to hold it up to the scene to be photographed and rotate. If the angle of light is right, blue skies become darker and the clouds stand out more, as trees and grass look greener. Itan effect that can add bottle to the picture, but the inherent increase in contrast is not always desirable. Ultimately, ita subjective call. And beware of using them with short lenses, as the effect on the sky is not uniform across the wide angle of view. A clear blue sky shot with a 24mm lens fitted with a polariser will show a donut effect of uneven tone depth which can look unsightly. Some say polarisers should never be used with wide angles; I think it depends on the sky. Clouds can mask the uneven polariser effect. FITTING YOUR FILTER Positioning ND grads is easy, just pull it down in the slot until it affects the area you want; Live View is useful for this. Metering and assessment of exposure are done in the normal way-by checking the histogram and highlight alerts after the filter is fitted. » Turn the polariser as you look through the eyepiece and just watch the world change. If you are using a polariser with resin ND grads, be aware that the polariser should be placed in front of the grads to guard against horrid patterning effects. » Super dense filters, like the Big Stopper, require the image to be composed and exposure calculated before the filter is attached. Take an exposure reading; calculate the 10-stop correction, either mentally, on your smart phone app or by using the chart supplied with the filter. Then set the camera s exposure mode to B, lock the shutter open and start pacing as you time how long the sensor needs to be receptive to the feeble light penetrating the dark glass. » Generally speaking, I try to avoid using more than two filters at the same time. The less glass in front of your lens the better, which is why Inot an advocate of skylight or UV filters as lens protectors. The best protection your lens has is a lens cap. Unnecessary glass just causes loss of lens performance and vignetting problems. Drop a lens with a skylight on and the most likely outcome is a shattered filter that has scratched the sacred front element with a bent filter ring that needs to be removed with a chisel. The Verdict Camera filters are not exactly high tech, but there s no getting away from the fact that they are damn useful. Modifying the light before it reaches the sensor allows us to achieve some effects that are simply impossible to replicate in post-production, and therea powerful argument in favour of getting it right in-camera. I use all the options available to me in search of the definitive image; camera filters, postproduction filters and exposure merging. They are all just tools at our disposal, and slaves to our creativity.

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