The smaller diagonal size of the DX format amounts to a narrower
angle of view than would be achieved with the 135 film format (35 mm film or
FX format), using a lens of the same focal length. Strictly in angle-of-view terms, the effect is equivalent to increasing focal length by 50% on a 135 film camera, and so is often described as a 1.5x
focal length multiplier. This effect can be advantageous for
telephoto and
macro photography as it produces a tighter crop without the need to increase actual focal length. However it becomes disadvantageous for wide-angle photography as a
wide-angle lens for 135 film effectively becomes a
normal lens for the DX format (e.g. 28 mm x 1.5 = 42 mm 135 film equiv.). This has led to the increased development of the DX format-specific lenses for the
Nikon F-mount. Since these lenses do not need to cover the 135 film area, they are smaller and lighter than their 135 format counterparts of equal angle-of-view. The production of DX-specific lenses has also enabled the production of affordable wide-angle lenses for the format (e.g., 12 mm), whereas costly ultra-wide-angle lenses from the 135 format were formerly required. When DX format lenses are used on 135 format cameras,
vignetting often occurs, as the
image circle does not cover the entire area of the 135 format. ==Active sensor size ==