How to avoid sun flares?
First, a filter does not help compared to not using one, since it adds a flat reflection surface. However, some filters add more flare than others. A filter that is multi-coated or – even better – super multi-coated adds less reflections and therefore less flare. To reduce flare if the sun is not shining directly into your lens, try a lens hood first. If it does not enough, then you need additional shading. Anything that does not obstruct the subject will do (hand, hat, a friend, etc). Keep in mind that if you use a full-frame lens on a cropped-sensor camera, the hood supplied with your lens cannot be adequate. This is also the case for a almost all zoom lenses at any focal other than its widest point.
