The dimming ratio indicates how many times the light filter reduces the intensity of the light flux passing through it. Each increase (ND) by 2 times means darkening by 1 exposure stop, respectively, the 4ND light filter attenuates the light flux by 2 exposure stops (x). It turns out 8ND — 3x, 16ND — 4x, 32ND — 5x and so on ... This parameter is important primarily for neutral filters (see "Type"). If after ND there is a large number (for example, 100 or more), it is logical that this is not a step (exposure value). To translate, you need to take the logarithm to the base of two.
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Multi-layer enlightenment. Enlightenment is the application of a special film to the glass surface, which improves light transmission by reducing reflections and scattering. With multilayer enlightenment, several such films are applied: firstly, this improves light transmission over the entire spectrum (since one film is designed for a rather narrow wavelength range), and secondly, additional layers (protective, water-repellent, etc.) .P.). In addition, multilayer coating significantly reduces colour distortion.
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Thin frame. Due to the thin frame, the filter takes up little space during installation, which allows you to install several filters on one lens at once. Thus, you can combine their effects as you wish.
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Wide angle. Light filters that can be used on wide-angle lenses. They can have a different design: it can be either a filter in a thin frame (see above), or a large-format glass that is larger than the diameter of the lens and mounted on a frame in the shape of a truncated cone, tapering towards the attachment point. Anyway, the main requirement for such a filter is that it does not restrict the field of view of the lens.
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Protective coating. The presence of a special protective coating on the filter glass, resistant to scratches. The characteristics and features of such a coating vary
...from manufacturer to manufacturer, this point should be clarified in the documentation for specific models.
— Waterproof. Moisture-proof light filters have a special coating — thanks to it, water falling on the glass flows almost immediately, without lingering and leaving small drops, spots, etc. This makes it easier to shoot in the rain and near bodies of water.
— Attachment with adapter. This type of mounting is mainly used for rectangular filters. The adapter consists of a ring for attaching to the lens and a filter holder, which, in turn, is attached to the ring. Actually, the filter plate is installed in the filter holder. This scheme allows you to use several filters of different types with the same adapter, changing them if necessary. And vice versa: adapters with different mounting diameters can be produced for the same filter (see "Diameter"), which allows using the same plate with different optics. At the same time, there is no single standard for filter holder sizes, and adapters are often sold separately from the filters themselves; therefore, when choosing such a system, it is worth making sure that the dimensions match.
