What kind of filter do I need to buy to get the best picture quality when shooting outdoor portraits with SLR cameras?

You should first understand the purpose of various commonly used filters:

Polarizers are mainly used to eliminate the reflection of nonmetallic surfaces, such as shooting fish in the water from the side. With a polarizer, the environmental scenery reflected by the water surface can be eliminated.

UV mirror is used to eliminate ultraviolet rays entering the lens. Because the sensor of a digital camera not only reacts to visible light, but also reacts to invisible infrared rays and ultraviolet rays, the UV mirror can eliminate these influential ultraviolet rays (infrared rays will be removed by the infrared cut-off filter in the camera).

Gray mirror, used for calendering or long exposure during the day.

The gradient lens is used to shoot scenes with great contrast, such as half the sky and half the mountain. With a gradient lens, you can only calendar the sky.

The starlight mirror is used to make the light source in the night scene produce luminous effect.

Soft-focus lens, used to produce fuzzy and hazy effects.

A color filter for filtering out a specific color.

Infrared mirror, using the characteristics of digital camera sensor can sense infrared light to shoot special infrared scenery film.

These filters are common filters, and some can be replaced by post-processing methods, such as soft focus, infrared, starlight and so on. Uv mirrors are generally useless (anti-100-200 yuan's ultraviolet rays will affect the image quality). Portrait shooting only needs to prepare a large aperture fixed-focus lens (generally equivalent to 70mm- 100mm belongs to the portrait focusing section), but the filter is not a necessity.