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Lens Test Using Test Charts

Purpose

Compare the 18-105mm power-zoom lens against other lenses, using a Nex-6.  Testing on this page was done on a tripod with OSS left on and using an infrared remote.  Results have to be considered somewhat approximate, as they are affected by various factors that are prone to errors, not to mention that the chart itself is not that exacting, as the granularity is fairly wide -- the gaps between measurements can be over 10% apart.  The limits of resolution depend on the sensor as well as the lens.  I'm using a 16mp sensor; better results may be had from a 24mp sensor.  ISO 400 was used for most of the shots, as light was a bit low, and in-camera JPEGs were used; I don't believe the ISO would largely affect the resolution, as NR was turned to low, but in-camera sharpening (even with the setting at "0") might.

Testing

I utilized the method described on Bob Atkin's site.  I used the factors from the chart in the finest grouping that allowed me to visualize 5 lines across.

In the below numbers, I'm choosing the resolution block that still clearly shows 5 lines.  However, this could be anywhere from, say, MTF 50 to MTF20.  What needs to happen is a deeper examination of the charts and a calculation of the MTF at each resolution (although, while I'm sure that this is prone to error, it has to be better than nothing).

Center

18-105, 20mm, F4.0: 74.6 lp/mm (75.3 with a 2nd test)
18-105, 30mm, F4.0: 68.2 lp/mm
18-105, 50mm, F4.0: 61.5 lp/mm
18-105, 105mm, F4.0: 61.1 lp/mm

18-105, 20mm, F5.6: 75.3 lp/mm 
18-105, 30mm, F5.6: 67.5 lp/mm  (Verified with a 2nd test)
18-105, 50mm, F5.6: 61.5 lp/mm
18-105, 105mm, F5.6: 61.2 lp/mm

E20, 20mm, F4.0: 74.7 lp/mm
E20, 20mm, F5.6: 74.8 lp/mm

16-50, 20mm, F4.0: 65.3 lp/mm
16-50, 20mm, F5.6: 73.9 lp/mm
16-50, 30mm, F5.6: 68.8 lp/mm
16-50, 50mm, F5.6: 67.0 lp/mm

Sigma 30, 30mm, F2.8: 70.4 lp/mm (slightly worse than at F4.0)
Sigma 30, 30mm, F4.0: 70.4 lp/mm
Sigma 30, 30mm, F5.6: 70.4 lp/mm (slightly better than F4.0, but not quite 77 lp/mm)

Edge

E20, 20mm, F4.0: 65.8 lp/mm
E20, 20mm, F5.6: 65.6 lp/mm

16-50, 20mm, F4.0: 65.3 lp/mm

18-105, 20mm, F4.0: 69.5 lp/mm

Conclusion

It's hard to know what to make of this test.  Since the resulting targets varied, I think it might be more accurate if MTF values were calculated.  As it is, it is probably OK for comparison within this particular test, and mostly between the same focal lengths.  Given that, I feel comfortable making the below conclusions:

The E20, 18-105, and 16-50 are all sharp in the center at 20mm, although the kit lens needs to be stopped-down for better results.

The Sigma 30 is better than the others at 30mm, as expected, although perhaps not by a whole lot.

While it seemed like this should have been a better approach to testing than my usual comparison shots, it left me searching for a better test.  See next page for more...

Originally created: July 12, 2015.
Last updated: July 18, 2015.