What Are the Different Types of Camera Filters?

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What Are the Different Types of Camera Filters?

Filters are available to improve the function of a camera and the quality of photographs it can take. They cannot compensate for poor-quality optical glass in a camera lens, and expectations should be realistic regarding what material the filters are placed in front of, as well as the material from which the filters are made. Another piece of glass or resin, polyester or polycarbonate placed between the lens and the viewed image can compromise the integrity of the photograph and contribute to image noise. Each material has advantages and disadvantages, and expense separates top-quality, easily breakable square or rectangular glass filters from thin, but durable polyester filters prone to scratches.

Filters will not correct longitudinal chromatic aberration (LCA) caused by focal distance, which can be reduced by stopping down an f-number. Transverse chromatic aberration (TCA) produces fringing different to that seen as ghosting in digital cameras using filters.

When light enters the lens through a filter, its dynamics change. This change, or Filter Factor, requires a compensatory adjustment to exposure. Each filter type has a specific FF which might demand an alteration to the f-stops up or down, so be aware of the difference and become familiar with the new settings.

Filter Shape

Filters may be round, square or rectangular. Each has a benefit. Round filters have threaded rims and screw directly onto the edge of the lens barrel. Variable size-ranges accommodate different camera model dimensions. Their close, tight fit reduces any opportunity for physical interference and keeps the filter near the lens.

Square or rectangular filters usually fix to a holder in front of the camera. Some may have slots to accept more than one filter for when layering is important. Rectangular filters are made as such to best manage the effect they produce.

Compared to a collection of individually sized filters, one standard filter, possibly 77mm with a set of step-up rings (circular or square) to fit onto lenses with smaller filter threads, limits expense. Conversion rings also minimise the bulk and weight of a complete set of matching filters. Stacking is possible by screwing one size into the next size (up or down) until the optimum size is achieved. Coupling the rings requires the male thread being matched to the lens' female thread. Sizes are labelled in mm in numbered pairs. The first number of the pair refers to the male thread for attachment, and the second number refers to the female thread for accepting further rings or other items, such as a lens cap. Thus, a ring labelled 28mm-37mm indicates the male thread is the narrower end and the female thread is the wider end, so this ring must be for stepping up. A ring with 77mm-72mm designation shows the male thread is wider and the female thread is narrower, so it is a step down ring to accept a smaller filter or accessory. Vignetting sometimes occurs with step-down rings, and professionals advise step up rings rather than step down rings where possible. The thinner the ring the closer it will keep a filter to the lens.

Ultra Violet (UV) Filters

A UV filter acts as a lens protector for digital cameras which already possess UV/IR protection in front of their sensors. For film cameras, it helps reduce haze that is apparent in outdoor shots with indistinct lines. Although these lenses are often called clear, their clearness or transparency is more accurately described as colourless.

Light scatter and reflection on an uncoated lens causes an estimated 4 per cent loss in light transmission. The visual echo continues to take up space and reduce the amount of usable light through a lens. Lens coating is so thin it does not significantly affect the surface upon which light acts, and its anti-reflective qualities greatly increase its ability to utilise light. Scratch-resistant coatings commonly use substances such as titanium dioxide, silicon, or magnesium fluoride (TiO2, SiO2,MgF2).

The best filters in this category have MRC (multi-resistant coating) or SMC (Super Multi Coating - the Pentax patented seven layer coating system) to minimise the possibility of ghosts, nasty reflections, or flares that spoil an image. Genuine MRC is detectable by the dark green/purple colour it reflects off any glass-to-air surface it has. A blue/amber reflection results from single coating and non-coated lenses share the same colour reflections since any incoming light might bounce.

Polarizers - Linear/Circular

To avoid glass and/or water reflections a polarizing filter is the item to use. The reduced glare and increased colour saturation, especially for skies, water or foliage subjects, is the polarized filter's main advantage. Just as sunglasses with polarized lenses improve a view, these filters make outstanding cloud and sky contrast, minimize haze, and remove reflection. A linear polarizing lens should not be used with a DSLR camera as it can interfere with the metering function.

Each time a camera uses a polarizing filter, ensure the relative position of the sun suits the level on the dial. Check differences between minimum and maximum polarization views, and adjust accordingly. Consider shutter speed when using a polarizing filter as it is not unusual for 2 stops of light to be lost when using them. Do not use them with a wide angle lens as there is a risk of sky-dark in the central area which will be difficult to fix post-processing. This same sky-dark can give an unnatural appearance when maximum polarization effect is used. Also, as polarizing filters are thicker than other types of filter, they are responsible at times for an unwelcome vignetting effect.

Warming/Cooling Filters

Occasionally the white balance of a photograph requires adjustment, as seen through the viewfinder in situ rather than after using software to create effects. When neither cooler blue daylight is desired nor a touch too much orange-red incandescent light, a colour balancing filter can restore the range required. Specialist landscape and underwater photography may benefit from these filters when overwhelming amounts of monochromatic light dominate the picture.

Colour Filters

Black and white film photography utilises red, green blue and orange filters for different effects that strengthen specific colours and highlight sky or foliage on trees, for example. Monochrome effect is enhanced by blocking one or other particular wavelengths of light visible to the human eye.

Graduated Neutral Density (GND)

Variations of GND filter include soft and hard graduation and reverse graduation. Essentially, hard and soft graduated filters are like dip-dye fabric. Soft graduation has a slow transition between colour and clear, whereas hard graduation features a distinct line separating the two that is used in alignment with the horizon when taking a shot. Reverse graduation filters feature the darker element at the centre of the filter rather than the top, moving up to lesser intensity. This provides suitable balanced exposure for scenic sunsets. They may also include specialist filters such as soft focus, dual image, or split field among others for special effects.

Neutral Density (ND)

Neutral density filters offer a solution to technical problems when diffraction could be a problem after slowing down shutter speeds or ISO speeds to increase exposure time. By uniformly reducing the amount of light that reaches a camera's sensor, it prevents fogginess that occurs when shooting falling water with insufficient stopping down. Apart from smoothing out moving water scenes, ND filters are also used to reduce field depth in bright light, introduce deliberate blur, or mask out visibly insignificant features of the composition.

Calculating the amount of light a particular ND filter will block depends on how the figure is represented by different manufacturers:

Extent of Uniform Light Reduction
(Neutral Density) ND
 

f/no
 

A/V
Aperture Value
 

Ratio
 

Equivalent Representations by Manufacturers
(to describe the density depth)

   
 

1. 4

1

1:2

1X

ND2 or ND2X

1. 3 ND
 

 

1. 0
 

2
 

1:4
 

4X
 

ND4 or ND4X

1. 6 ND

 

1. 8

3
 

1:8
 

8X

ND8 or ND8X

1. 9 ND

 

1. 0
 

4

1:16

16X

ND16 or ND16X

1. 2 ND
 

 

1. 6

5

1:32

32X

ND32 or ND32X

1. 5 ND

 

8

6

1:64

64X

ND64 or ND64X

1. 8 ND

Conclusion

Although filters cost less than lenses, they remain a considered expense. They require care to maintain their cleanliness and transparency, and when speed of action matters to a photographer, ease of cleaning may be a concern. Finer construction for thinner step up or step down rings can make them fragile. The materials used to manufacture equipment determine their robustness, and this is reflected in the price of many parts using technologically advanced elements.

Familiarity with one model does not guarantee the transfer of knowledge to a different one. Experimentation and practice using the filters will reveal their possibilities and limitations. It is best to try them out in a variety of situations to understand the vagaries and influences of different circumstances when photographing outdoors and in variable light settings.

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