1. Soft Focus Filter: The function of the soft focus filter is to partially refract the light passing through the lens, allowing the captured image to maintain a certain level of clarity while also achieving softer and more natural tonal contrast. Soft focus filters come in various constructions, typically featuring circular patterns of varying density etched onto transparent glass, or nylon mesh or other fiber materials that split and refract incoming light. When using a soft focus filter, especially for close-up portraits of women and children, the images produced will have a smooth and pleasing effect.
2. Diffusion Filter: Structurally, a diffusion filter consists of a glass lens with a hole in the middle and a sand-like texture around the edges. Due to the central opening, when mounted on the front of the lens, it does not affect the focusing of the main subject. When photographing people, positioning the face within the hole allows for normal sharpness, while the areas outside the face become blurred due to the sand-like texture of the filter. It is preferable to use a single-lens reflex camera when employing a diffusion filter, as the photographer can directly observe the blurring effect through the camera's viewfinder.
3. Close-Up Filter: Also known as a portrait filter, the close-up filter is a convex positive lens that, when attached, shortens the focal length of the lens and thereby reduces the minimum focusing distance. This enlarges the subject's image, fully utilizing the film area. Generally, no additional exposure compensation is needed during shooting, but a small aperture should be used to increase depth of field and prevent corner softness in the negative. In practice, close-up filters are not recommended for extreme close-ups of people, as the shorter shooting distance can cause distortion.
In addition to these commonly used attachments, there are also multi-image filters, starlight filters, neutral density filters, and other special effect filters. The first two create multiple images and different radiating starbursts respectively, while the latter reduces the amount of light passing through the lens. These effects won't be elaborated further here.