Introduction to filters

Many filters that are crucial in analog photography are not particularly useful in digital photography. Numerous filters that are used in analog photography can be simulated in an improved and controlled manner on the computer. However, there are some filters that still fulfil their purpose and are still used (e.g., polarising filters, ND filters, grey filters, grey graduation filter…) and cannot be simulated using the computer. The article provides an overview of the topic „Filters in photography“. The links provide even more information about this topic.

Construction, terms and technical features of filters
Screw-in filters
There are two types of camera lens filters. The most common type is the screw-in filter. They are screwed into the threads at the edge of the lens barrel. The width of the filter has to be the same as that of the lens thread. The size of the filters is indicated in millimetres. In (digital) 35mm film, you generally come across these sizes: 49mm, 55mm,  58mm, 62mm, 67mm, 72mm, 77mm, 82mm, 86mm.

Slot-in filters
A different type of filter is the slot-in filter. Here the filters are slotted into a filter holder (e.g., the Cokin filters). In this system, the filters are not just made of glass. There are also filters made out of plastic in varying degrees of thickness. In particular wide angle lenses sometimes have special filter holders inside the lens. This reduces the problem of convex front lenses and vignetting.


Adapter rings
Using adapter rings screw-in filters can be used on lens with different widths. This allows you to use various lenses. However, it is often the case that the lens hood then no longer fits. The lens cap then also no longer fits. Careful! It is only useful to incorporate an adapter when using larger filters on smaller lens widths. On the adapters, you will find two pieces of information: the size of the inner thread (this is where the filter is placed) and the size of the outer thread (must be part of the lens) of the adapter ring. The description 52à 55 on an adapter indicates that a 55mm filter can be adapted to a 52mm lens.


Thickness of filter holder

For extreme wide angle shots, it is also important that the filter holder is not too thick. Otherwise this could result in shadows on the edges of an image. The disadvantage of thin filter holders or mounts is that the normal lens caps cannot engage properly and you may not be able to use them. Filters with particularly thin filter holders are often marked as “slim line”.


Filter factor

Some filters only allow some light to pass through. This would result in dark images if the settings such as diaphragm, exposure and ISO rate were to remain the same. Most modern cameras however have a TTL meter (Through the Lens). This metering system automatically factors in the impact of the filter when metering exposure. The camera then (in most auto programs) compensates exposure, diaphragm or ISO rate during the exposure period to ensure that the exposure remains the same. The filter factor tells you to what extent exposure, diaphragm or ISO rate have be changed in order to maintain the same exposure.

More information on photographic filters can be found here for example: http://en.wikipedia.org/wiki/Photographic_filter

 

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