Controlling Contrast is difficult in bright sunlit exteriors. Exposing for either highlights or shadows will leave the other severely under-or over-exposed.
Tiffen 5.650"x5.650" Soft Contrast Filters 1, 2 include a light absorbing element in the filter which, without exposure compensation, will reduce contrast by also darkening highlights. Use this latter filter when lighter shadows are not desired. In both cases, the mild flare produced from bright highlights is sometimes used as a lighting effect.