Monday, May 9, 2011

Bokeh Comprison: Nikon AF 50mm f/1.4 D verses Tamron 17-50 f/2.8

The Nikon 50 AF-D and the Tamron 17-50 are both common lenses that are often found in the bag of serious enthusiast shooters. Much has been said about using 50mm lenses on crop frame cameras for portraits, so the question is, can a fast-zoom do the same in a pinch? The following was the same for both lenses:
  • ISO 100
  • f/2.8
  • 1/250 seconds
  • 50mm
I chose f/2.8 for obvious reasons, namely that the Tamron only opens up to f/2.8. However, given the challenges of producing an acceptably sharp image at f/1.4, it's fairly reasonable to suggest that many people would find use for the Nikon at settings other than completely wide open.

First the Nikon.

Nikon 50mm AF-D
Now the Tamron.
Tamron 17-50

Even though the focal lengths and exposure settings are the same, the camera (a D80 in this case) meters differently with each lens. The Tamron actually meters more darkly... I tweaked the exposures to try to keep both images comparable. Within the plane of focus, sharpness is about equal for both lenses, but the background rendition is visibly different. The Nikon is visibly smoother, whereas the Tamron is busier and harsher.

Take home points:
  • Bokeh refers to the quality of the out of focus areas of a picture, and not just the amount. Extreme foreground/background isolation is not necessarily good bokeh
  • Lens with the same focal length and shot under the same conditions can produce different qualities of bokeh
  • Though fast zooms are very convenient, the old standby 50mm still does something that an all-in-one solution doesn't, and is a small cheap item to pack in a camera bag.
  • You don't have to shoot wide open all of the time to get reasonable bokeh. 
  • Even though there are are lot of lens that do f/2.8 at 50mm, the 50mm will still be superior in portrait applications at the exact same settings.

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