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Here is a head to head comparison of the Nikon 18-70mm f/3.5-4.5G ED-IF AF-S DX and 50mm f1.8D AF prime lenses.
The D70 camera settings were:
JPG-Fine, aperture priority, Exposure Comp +1.0EV, ISO 200, WB Cloudy, AF-S, all images auto-focus,
color mode Ia, Tone comp: Normal, Hue adjustment: 0 deg, Saturation: normal,
sharpening: normal, shutter speed between 1/20th and 10 seconds depending on aperture. The tripod is
a Bogen 3051 with a heavy pan/tilt head - a beast.
The 50mm was done first then the 18-70mm was set to 50mm. I made sure the 18-70mm was at
50mm by shooting and adjusting the lens until the camera LCD indicated the lenses were shooting at 50mm. The
light was becoming progressively more blue and only 2 minutes passed between lens tests. The test was done after the
wall was in the shade. I used the histogram to try and make the exposures relatively equal. The 18-70mm required an
higher exposure compensation of EV +1.3 because I've found my lens is off by -0.3EV.
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| f-stop | 50mm f1.8 AF | 18-70mm f/3.5-4.5G ED-IF AF-S DX |
| f 1.8 |  | N/A |
| f 2 |  | N/A |
| f 2.8 |  | N/A |
| f 4 (18-70 was at f4.5) |  |  |
| f 5.6 |  |  |
| f 8 |  |  |
| f 11 |  |  |
| f 16 |  | |
| f 22 |  |  |
50mm Sharpness data
Using the JPG file size as an indicator of sharpness, several series of shots were taken with the 50mm f1.8 lens on a heavy
Bogen 3051 tripod with matching pan-tilt head. The favorite subject, a brick wall, was used to conduct these tests.
Between every series, the camera was refocused using autofocus. The camera body was made parallel to the wall to help
eliminate depth of field reductions in the sharpness measurement.
Graph 1: Nikon 50mm f1.8 aperture sharpness
From graph 1, it can be seen that my particular
50mm Nikon lens sample performs best at f5.6. These numbers cannot be compared against other lenses, as I
do not have a baseline standard for comparison. This graph only provide information about the sharpness
of my Nikon 50mm lens sample at various apertures. Lens sharpness rolls off at f16 and f22 due to diffraction, as expected.
Note that the scale of the graph overemphasizes the relative reduction in sharpness. At full scale, there is
not a huge sharpness difference.
Conclusion
The 50mm prime was strong at all apertures but f1.8, f2, f16 and f22. There is a marked decrease in image sharpness from
f16 to f22 on both lenses, as is expected when the lens becomes diffraction limited. The 18-70mm doesn't hold a candle to
the sharpness of the 50mm. For $110US, the 50mm f1.8 is probably the best sharpness for dollar in the Nikon lens arsenal.
Comparing the two lenses makes the 18-70mm look terrible though it's not that bad. I just don't have another zoom covering 50mm to compare
and show the relative strength of the 18-70mm.
If you would like to see
the lens aperture affect in a progressive way, download each of the images above, put them into a folder and quickly flip through viewing them in Window Fax/Image viewer or Mac iPhoto. Using the
flip-book technique is how I did my initial assessment of how each lens was performing.
Back to main lens comparison.
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