Guide to Photographic Filters in Digital Photography

The world of filters in digital photography: learn to choose and use various types of photographic filters to enhance your images.

Author: Marco Crupi

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This article is a segment of the Digital Photography Course. Click here to return to the main course overview.

In digital photography, it’s possible to apply in post-production the effects that were once only achievable during shooting. Despite this, photographic filters are still on the market, because some of them are still useful and their effects cannot be recreated in Photoshop.

COLORED FILTERS

Colored photographic filters.

It’s rare to see photographers use colored filters nowadays. They were very popular in the era of analog black-and-white photography, primarily used by landscape photographers to lighten or darken certain areas of the image. Today, their effect can be 100% recreated with post-production software.

In Photoshop, simply go to “Image -> Adjustments -> Black & White” to start experimenting immediately with how these filters affect our images.

POLARIZING FILTERS

Polarizing filter.

Contrarily, a polarizing filter is a must-have in a photographer’s kit because its effects are not replicable with any software.

It’s used to polarize light reflected from object surfaces and atmospheric particles, essentially removing reflections from all non-metallic surfaces and ensuring maximum contrast.

It also removes unwanted reflections from water surfaces but can also enhance them. Simply rotating it achieves the desired effect. In both example photos below, I used a polarizer, but depending on how I rotated it, the reflections on the water’s surface decreased or increased. In the photo where the reflection is attenuated, the bottom is clearly visible.

When photographing a shop window with a polarizing filter, we can avoid being reflected in it, hence it’s used for photographing paintings or other works protected by glass.

Without polarizing filter.

With polarizing filter.

There are two types of polarizers:

  • Linear, which can cause problems when used with cameras having the exposure and AF sensor behind partially reflective elements (like the mirror). To avoid autofocus and light meter malfunctions, it’s recommended to use a circular polarizer.
  • Circular, as just mentioned, on autofocus cameras, the polarizer must be circular. It’s mounted on the lens, and rotating it can achieve different effects visible directly through the camera’s viewfinder.

This filter has no effect if shooting with the sun directly in front or behind: we must be between 45° and 90° to get good results. Also, it absorbs about -2 stops of light.

Thanks to the polarizer, we can achieve natural color saturation in the shot, avoiding the need to force it in post-production. This effect is due to the elimination of reflected light. In landscape photography, they’re used to give more depth to blue skies and to more clearly separate various color tones.

Photo taken with a polarizing filter and processed in Photoshop.

This last part regarding the better separation of color tones thanks to the use of a polarizing filter is of considerable importance in black and white landscape photography. Let’s see why immediately with an example made by taking two photos with the same framing and black and white post-production, the only variable that changes is the use of the polarizing filter.

Photo with polarizer.

Photo without polarizer.

Photo with polarizer converted to black and white.

Photo without polarizer converted to black and white.

I want to emphasize that the exposure in the original shots was perfectly correct, ISO 100 – F/13 – 1/40 sec. for the one with the polarizer, ISO 100 – F13 – 1/160 for the one without the polarizer (the ambient light was that of early afternoon on a summer day in Sicily).

Having a narrower range of tones to work with in the photo without the polarizer, it’s not possible to create a clear difference in terms of brightness and shades of black and white between the various parts of the image, lowering the “Blue” to -100 in the HSL panel of Lightroom darkens the entire photo.

Whereas in the photo where I used the polarizer, I have such a range of tones to work with that by lowering the value concerning the “Blue,” only certain parts of the image became dark, namely the sky, excluding clouds, which remained on white – light gray, and some parts of the sea.

I could even create a greater contrast between the various shades of the sea, something impossible in the photo without the polarizer, where I didn’t even have the possibility to “separate” it from the sky.

ND FILTERS (NEUTRAL DENSITY)

Another type of filter that cannot be reproduced with Photoshop is the ND (neutral density) filter. Its effect consists in altering the exposure without introducing any color dominance. There are various types, named as follows: ND2, ND4, ND8, etc. This classification is based on the reduction of light they can cause.

This filter looks dark gray/black, reducing light by one stop for ND2, two stops for ND4, three stops for ND8, and so forth. The table lists all types of neutral density filters and their respective stops of light reduction.

But why reduce light? There are practical situations where, no matter how much we close the diaphragm or lower the ISO, the light is always too much, for example, when we want to take a photo with a very long exposure time in broad daylight.

The photos you see are taken using an ND1000 filter.

Photo taken with ND1000 filter.

Photo taken with ND1000 filter.

Il mio filtro ND1000 è così scuro che fotografandolo mi vedo riflesso invece di vedere cosa c’è dietro di esso.

ND 1000 filter.

GND FILTERS (GRADUATED NEUTRAL DENSITY)

The last type of filters that we can’t reproduce is the GND (graduated or also called graduated neutral density) filters. As the name suggests, these are filters that graduate from top to bottom, i.e., transparent at the bottom and darker at the top, helping to balance exposure changes in a scene, for example in a landscape they allow to shield the sky more than the ground line below the horizon.

GND filter.

It’s better to use the sheet ones (there are also screw-on ones) because they allow us to adjust the height as we wish so that the change in density matches the horizon line. They are very useful for rebalancing the light levels of a too-bright sky and a dark foreground: haven’t you ever experienced that during a photo of an urban or natural landscape, the trees or buildings are correctly exposed while the sky is overexposed? Using one of these filters, you can solve the problem. Be careful that the dark area does not go below the horizon, the effect might not look natural.

Photo without GND.

Photo with GND.

As you can see, in the second photo, the use of the GND filter allows me to maintain correct exposure on the sea and beach, avoiding an overexposed sky, which gives me more room for maneuver in post-production, working on a correctly exposed sky is quite another thing than working on a sky that might have burnt whites.

In the first photo, instead, where I did not mount the GND filter, the camera had to find a compromise to regulate the exposure between the various parts of the image, the difference between the two photos is quite evident.

Of graduated filters, we find two types: soft and hard. The hard ones are suitable for very clear boundary lines like the sea, while the soft ones have a softer gradient, suitable for example, in case of mountainous landscapes or those featuring trees, essentially all those landscapes that present a not well-defined horizon line.

Reverse graduated filter.

For sunsets over the sea with frontal sun, it is advisable to use reverse graduated which are soft in reverse, i.e., they are hard in the middle of the plate and fade to soft upwards.

PROTECTIVE FILTER

Protective filter.

A filter that has no effect on the image but is still very useful is the protective filter, which as the name suggests is used to protect our lens from bumps and scratches.

If you decide to use it (although the lens hood is still protection for the front lens), I recommend not saving too much because a low-quality protective filter could negatively affect the image quality.

ADAPTER RINGS

Filter adapter rings.

After analyzing the various types of filters, a practical consideration must be made: usually, a photographer does not have only one lens, and very rarely will they have the same diameter, so a specific filter would be needed for each lens, leading to increased expenses. Fortunately, there are adapter rings that allow us to mount the same filter on multiple lenses of different diameters.

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