In Spite of its Extremely Low Price The Lens Build Quality is Very Good
Very few lenses are any sharper than a classic 50mm normal lens at a medium aperture setting so let's look at the Nikon50mm f/1.8 AF D, a lens that surely has its rightful spot in a great number of camera bags with thanks to its bottom end price tag and extremely light weight. This test was performed mounted on a Nikon D90, DSLR APS-C camera which has a 1.5x crop factor. There is a 75mm equivalent field-of-view compared to a full frame FX camera so this normal lens corresponds to a moderate telephoto lens within this latitude.
The optical build is created with 6 elements within 5 groups and no special elements. There is a minimum focus distance of 0.45m which results in a maximum. 1:6.6 object magnification. Additionally the thread size of the filter is Nikon's typical 52mm. As stated above this prime lens is an extremely compact (64x39mm) and weighs very little (155g). The aperture apparatus sports 7 total aperture blades.
In spite of its extremely low price the lens build quality is very good. The outer lens barrel is created with polycarbonate (plastic) with an attached metal mount. A very small focus ring with rubberized covering functions very smoothly. The lens extends just a little forward when shooting at closer focusing distances. The front lens element doesn't turn so shooting with a polarizer filter is a breeze. There is no internal autofocus motor in the lens, but depends upon a slotted screw drive controlled by the camera. Consequently AF operations generate a moderate noise level. The AF speed becomes decent when mounted on a D90.
Distortions No surprises for a fixed focal length lens. The barrel distortions are incredibly low (0.26%) which is nothing to get excited over.
With thanks to the D90's sweet spot behavior, vignetting is under control. Wide-open aperture vignetting is somewhat stronger while at ~0.66EV allowing
visibility in very critical operations. At f/2.8 and beyond the problem goes away.
Normal lenses turn in stellar performances when employed with medium aperture adjustments and this Nikkor 50mm f/1.8 AF D is not an exception. At f/4-f/8 it's it gets no better than this on the D90 turning an excellent middle and very-good border implementation. Although it is also rather typical in ultra-large aperture lens that things are not quite as peachy shooting wide-open although the center is excellent already although the borders are somewhat soft in combination with low contrast. At f/2.8 and on the MTF50 curve distribution implies the center performance is superior to the D90's quality. The borders continuously improve with good numbers at f/2.8 with very-good performance at f/4.
The 50mm f/1.8 allowed slight residual spherical aberration (focus shift stopped down).
Chromatic Aberration (CA)
Chromatic aberration (color shadow with harsh disparity transitions) are comparatively pronounced for a fixed focal lens with an average 1.2 pixel width along the image borders. Nevertheless this s not a big issue. Stopping down changes the issue to more moderate numbers.
The Nikon 50mm f/1.8 D lens is low profile with less pizzazz than big glass lenses but still is an appealing lens however. When the aperture is wide-open it is a bit soft along the image borders while the level of contrast is somewhat in the low numbers. Although, at medium aperture positions the resolution numbers become exceptionally high and a benchmark to surpass for sure. Distortions are next to nothing and any vignetting is well under control. The build lens quality is very respectable while the AF accomplishment does not leave anything to be wanted.
Plasticy feeling build,
Autofocus is noisy although very reasonable, A
75mm equivalent on DSLR DX is a strange focal length for normal lens. although I find it useful.
Apr 1, 2011
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These shots were hand held. Click a Photo for Larger Image