If you only buy one filter

make it a circular polariser. This is the perfect beginner's filter, and one that will have the biggest effect on your day to day photography, giving holiday skies a vibrant blue tone and accentuating the contrast between the sky and passing clouds to afford your images greater texture. Although you can add blue to your images in Photoshop or a similar post-production editing tool, the effect is never as believable when done that way as it is when shot using a lens.Invest in an inexpensive circular polariser to improve the blue of skies in your images.