A glass filter that reduces exposure by approximately 10 stops.
The simple answer to this is yes! Although your images can be edited using imaging programs such as Photoshop, there are some filters that you just can not mimic its results in imaging programs. A suggested type of filter is a UV or Ultra-Violet. While ultraviolet light is invisible to the human eye, it can nevertheless show up on a film image as an undesirable blueish cast; it can even result in a blurring effect. Recommended to be used as a means of protection for the lens (digital slr included), these filters can be left on at all times as it is completely clear and will not change the colour or density of light. Ideal for photography of expansive spaces like mountains and sweeping landscapes.
The second helpful type is a polarizing filter. Reflections of water and other reflective surfaces, like glass, can cause major problems for your images. Polarizing or polarizer filters can fix them because they remove glare from non-metallic surfaces, ensuring a crisp, clear, more colour saturated image. Reflected light can also wash out an image, but polarizing filters combat this nicely by producing deeper colour saturation. Ideal for outdoor photography, a polarizing filter can be rotated for desired effects and the results will produce dramatic blue skies and better contrast and colour.