Sweet spot of the 18-105 lens?

Started Aug 24, 2010 | Discussions thread
Brooks P Veteran Member • Posts: 9,183
Re: Sweet spot of the 18-105 lens?

When you say sweet spot, are you speaking entirely about resolution?

You can view PhotoZone’s test results here http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/410-nikkor_18105_3556vr?start=1 .

Distortion is really bad at 18mm, is practically non-existent at 24mm and then starts creeping back in as the focal length increases out to 50mm; somewhere between 50mm and 105mm the distortion begins to edge down – ever so slightly.

MTF (resolution) numbers reveal that the highest rating (2206.5) the number of line widths per picture height (LW/PH) occurs at a focal length of 18mm and an aperture of f/5.6 for the center measurement; the Border measurement for the same setting is 2029.5, and the Extreme (corners) rating is 1834.5.

At 24mm f/5.6 holds on to the high rating (2204) and the Border has increased to 2074.5, and the Border to 1949. The across lens rating is better at 24mm than at 18mm although the highest rating occurs at 18mm.

At 35mm both the Center and the Border are squarely in the Excellent range (1950 – 2250). At 50mm only f/8 has both Center and Border number that rate Excellent. At 105 the Center rating is Excellent from f/5.6 – f/11, while the Border numbers are all in the Very Good category.

None of this takes into account DOF and if 24mm and f/5.6 don’t meet your needs for the current shot then what difference does it make if that happens to be the sweet spot?

Another thing to consider is that while LW/PH can be measured under controlled conditions in a lab it is extremely doubtful that the human eye can detect much, if any, difference between 2113, 2174, 2138, or even 1985 LW/PH. Those are the numbers for the Center measurement at 35mm for F/4.5, F/5.6, F/8, and f/11 – don’t get hung-up on lab results when you are shooting in the real world. I have read that camera shake, even with VR, can reduce apparent resolution to below that of the lowest numbers achieved in the lab. So while you may be shooting at 24mm with an aperture of f/5.6 and the lab results indicate that 2204 LW/PH is the resolution for that setting, real world conditions may be more like 1650-1950.

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Amateurs change camera settings to match the light; Pro’s change the light to match their needs.


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