My filter case 

A tutorial.

There are just so many filters available, and this can become quite daunting and confusing if you have no idea what it is that you are looking to buy. Your choice of filters that you will end up using is going to depend entirely on the type of photography that you wish to pursue or the discipline that you want to follow.

I am only going to look at three areas that could be of interest to you. There are many more, and usually, each discipline would have filters, especially to help you achieve your desired effect.

These three areas that we will be looking at include landscape, beauty and general photography. I like to know what I am working with and how the filters work and what should I avoid and be careful of going wrong. So before we get into this, let’s find out about filters.

Primarily all filters are made from coloured glass or acetate disks designed and constructed to modify the light passing through them used to alter the appearance of the final photograph.

 

Colour correction, colour conversion and a neutral density filter, differing filter threads.

Polarising filters

One of the essential filters that you should have in your camera bag is a polarizing filter. Polarizing filters typically have two uses. Used over camera lenses and light sources to reduce or remove specular reflections from the surfaces of non-metallic surfaces. A polarizer aids in reducing reflections and glare by filtering out light that has become polarized due to reflections from non-metallic surfaces. Essentially, this means it cuts down on certain types of light in a way that can benefit your photography. This filter can help reduce or eliminate reflections on glass or water, reduce some reflected light on specific subjects, or improve overall contrast in a landscape.

It helps to keep in mind that when shooting outdoors polarizers work best with the camera pointed 90º away from the sun. The filter is also handy in that it will allow you to increase the contrast in the sky by causing clouds to stand apart from the background and the blue sky to appear much darker and also reflections from standing water will be removed or reduced. If you were using a digital camera, you would buy a circular polarizer and not a linear polarizer as used in the days of film. Circular polarizers have an extra quarter wave-plane element that helps convert the light back into a form that is suitable for modern autofocus cameras.

For the technophobes amongst us, a polarizing filter is, in essence, a diffraction grating! A diffraction grating is an optical element with an intermittent structure that splits and diffracts light into several beams travelling in different directions. Stated, it allows only one set of rays of the sun to strike the surface of the sensor. All polarizing filters have a screw ring that will enable you to rotate the screen until you can see the effect through the viewfinder. Light is known to travel in a wave motion along a straight path, vibrating in all directions. Polarization is brought about by a polarizing filter, which causes light to vibrate in a single plane only, reducing its strength and without the use of the polarizing effect is typically used as a neutral density filter.

Neutral Density Filters

The second group of filters that you should have in your camera bag is a or group of neutral density filters. A neutral density or ND filter is a filter that is used to darken or lower the amount of light that passes through the lens by a specified number of stops, ranging from a fraction of a stop to 10 stops or more. Uses for neutral density filters include shooting in bright light with a fast aperture for shallow depth of field and taking long exposures during the day. Often referred to as a ‘black filter’ has differing strengths of grey in appearance. Every filter manufactured has a filter factor, which is the amount of exposure increase that is needed to be given to us from the manufacturer.

The cameras light meter will adjust for the factor but to help us we need to understand that a filter with a factor of 2 will increase the exposure by one f stop or increase the shutter speed by doubling, i.e. from 1/125th to a 1/60th etc. All filters are typically sold with a filter factor starting from 1 and expand from there. A filter factor of 2 would result in a one-stop adjustment, a filter factor of 4 a two-stop adjustment, a filter factor of 8 a three-stop adjustment and 16 a four-stop adjustment and so it continues. Notice how the filter factors double, 1, 2, 4, 6, 8, 16 and the exposure stops incrementally, 1, 2, 3, 4 stops etc. If you have grasped this, you would have absolutely no problem in selectively applying and controlling subject motion in the scene that you are attempting to photograph.

A different strength or value of a neutral density filter is obtained by cutting out the intensity of light equally from each of the colour primaries at all wavelengths having an equal opacity to all the colours of the spectrum. Neutral density filters are manufactured in different strengths commonly know as the filter factor and measured accordingly in exposure value, f stops.

By using a graded neutral density filter, it was possible to render the water flowing over the rocks to appear smooth. The clouds were static, and not much movement can be detected. 

In this image both the foreground and background are rendered smooth. This exposure could have been for a few minutes. (Image courtesy Apple Computer corporation)

Soft Focus and Beauty 

The third group of filters commonly know as soft focus filters are used to soften wrinkles and blemishes in beauty portraiture. Cokin made the filter I most often used, their 083 which had the mildest effect. Their 084 and the 085 being the most pronounced. These filter have minimal impact on the sharpness of the image. They are also used to reduce contrast by diffusing the highlights. I used this filter often to soften skin texture when I was doing a beauty shoot and for selected wedding portraits.

Diffusion filters: Reduces Highlights and Lowers Contrast. Softens Wrinkles and Blemishes. Creates a Soft Quality of Light.

There were times that I used a UV (ultraviolet) or Skylight filter with a very thin smeer of petroleum jelly and made my soft focus filter create a soft quality of light. I had a window display dummy in my studio to practice with and was often surprised by the different effects I was able to achieve. Petroleum jelly can become quite messy, so do this carefully, and I am sure that you will be as pleased as I was. When the shoot was over, I cleaned the filter by using a paper towel and then surgical spirits. All good, with the result being worth the effort that this was needed to use this technique. It was also possible to buy a cemera lens that was specially manufactured to produce this softened effect.

 

The Canon EF 135mm f/2.8 With Softfocus Lens is a relatively small, light and inexpensive 135mm lens. The unusual feature of this lens is its softfocus capability. The 135 L has a ring that allows continuous soft focus settings ranging from locked at 0 (none) to 2 with detents at settings 1 and 2. Set at 0 (no effect), the 135 softfocus lens is somewhat soft open (f/2.8) and, like many other lenses, becomes sharper as it is stopped down. Corner sharpness trails the center of the frame by a stop or more. So this is a somewhat-sharp soft-focus lens? As Canon carefully denotes this lens as being “With Softfocus”, a soft focus setting of 0 allows this lens to function like a standard 135mm lens.

Colour Temperature

In the days of film cameras, no electronic or digital manipulation of white balance was possible. Either the exact film was used for the specific colour temperature of the light source. This was measured in degrees Kelvin and referred to as ether daylight or tungsten film. Daylight film has a colour temperature of approximately 5200ºK and tungsten film 3200ºK. If theses films were used in the wrong lighting conditions a pronounced colour cast would be detected. This is commonly termed ‘colour balance’ Digital cameras can manually set for the correct colour balance according to the light source that you find yourself in but in my own experience auto white balance is selected and most of the time the camera sorts out the white balance problem for us.

 

Some digital camera forums dissuade you from using a UV or Skylight filter as a means of protecting your lens. The use of these filters can adversely affect your image when working at the extremes of your ISO range, trying to squeeze the most out of this feature. In my entire professional experience, I refused to use my camera lenses without having a ‘protection filter in place over the lens.’ Your camera lens is, in my opinion, an essential tool in your camera collection, so use this carefully and willingly choose to protect the front lens element. If you do have an extreme wide-angle lens on your camera, you could have vignetting problems commonly known as light fall-off where you can see the image corners darkened compared to the centre. There are ultra-thin purpose-built filters that will overcome this problem. Remove this filter if you absolutely have to but immediately replace this once your photograph has been taken.

There is just so much more to say about the choice and use of filters in your photography. This brief tutorial intended to give you some insight into their many benefits and to set you on a path of discovery. There is useful information available, and for further improvement, I have included a video that will prove to be helpful