The idea for a general discussion on photography filters, especially those in landscape photography, came to me while working on the recent article about the polariser. Here's to explore the topic further and provide some advice on applying filters in practice as well as replicating some of their effects in post-processing.
Photography filters – as far as landscape photography is concerned – seem to disappear from the scene rather rapidly, which is a pity. The skylight filter is one of the few still around.
It is most commonly used in landscape photography to prevent a bluish haze forming around distant objects, such as mountains. The effect is caused by scattered light reflected from the sky, thus the moniker.
When made of glass, the filter will also reduce the amount of UV light reaching the lens. Both filter effects result in a slightly warmer rendering of the final image.
The most useful application of the skylight filter, though, lies in the protection it provides for the lens behind it. For this alone, the filter is well worth keeping attached to each of your lenses, especially as it won't cost you a fortune.
The filter has no effect on exposure and will work in combination with any other, often more expensive photography filters protecting them as well, if required.
I briefly mentioned the filter in the introduction article on tips for landscape photographers. If your camera doesn't have one built-in, consider adding some of its variety to your gear. The filter gets often denoted as ND grey.
The ND filter usually comprises a round piece of glass or plastic tinted in some shade of grey. Its declared purpose is to trap, or absorb, the light before it can enter the lens. The darker the filter, the more light gets prevented from reaching the lens, and the longer exposure time becomes available/is required to capture a scene.
This is the main idea behind the filter: to allow for slower shutter speeds, especially in combination with wider apertures. The more or less standard filter grade is -3 EV, guiding one eighth of the available light to the lens. This is also the most common value for neutral density photography filters built into cameras.
There are much more extreme – and accordingly expensive – varieties, like -9 EV grade filter, capable of day-for-night cinema effects with its transmission factor of less than 0.2%.
Can you verify the last number?
Related to the neutral density family and often carrying its signature "ND" in the name, the graduated filter features a smooth transition from transparent to dark grey across its surface. The idea is to place the dark end along the upper part of the lens to prevent blown highlights in the sky when exposing for the lower, shadowy part of the image unaffected by filter's transparent end. The graduation makes sure that no hard edges scar the image, and keeps the overall contrast at bay.
Graduated filters have been in use by landscape photographers for decades. They actually haven't lost any of their importance. After all, the sky is still brighter than the rest of the landscape when someone fetches her camera to take a shot. However, the filter becomes a rarity, slowly but surely.
The decline probably owes something to usability. The filter isn't a screw-on type. It isn't even round. A square plate made of glass or gelatine is held in place by two sliding guides. The guides themselves are attached to an adapter screwed onto the lens. This isn't exactly a construction you'd swap around shot for shot.
The usual proceedings require mounting the camera on a tripod, composing and framing the image, then exactly aligning the filter according to the scene, i.e., moving it up and down to cover the brightest area of the sky with filter's own darkest region.
At this time and age, who's got the nerve? Aside from a few professional photographers and dedicated amateurs... You guess.
The bad news is, hardly! If filters mentioned above were absent when you took the images, there's little you can do in post-processing, especially if you managed to knock your bare lens against a tree on location (keyword "skylight").
The good news is, if you exposed for the sky, you'll be able to use the gradient tool for a graduated filter in Photoshop to recover the shadows. Follow the steps below:
This technique works as well every time you want to lift shadows in some part of your image. For example, use radial gradient out of the image centre to get rid of heavy vignetting in the corners.
Tags: #landscapephotography #lensfilters #photogear
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