The Importance of Lens Quality

2012.10.11

The Nikon D600 was introduced last month as the lowest cost full-frame DSLR available. As a matter of fact, it still is and will likely keep its position when the Canon EOS 6D arrives, despite the latter have a slightly lower suggested retail price. Even though it slots itself below other full-frame offerings, the 24 megapixels D600 is a serious professional-level DSLR with dual control-dials, a 100% coverage viewfinder, a weather-sealed body, dual-axis digital level and a hot-shoe plus built-in flash with remote control capability.

The headline feature of the D600 is price and it is currently available for $2096, making a full-frame DSLR more affordable then before. Having a good budget for lenses has always been recommended and a 24 megapixels digital camera like this one makes it clearer than ever.

For the upcoming full-length review of the Nikon D600, we have been working so far with two lenses, the high-end Nikkor 24-70mm F/2.8 and the versatile Nikkor 24-120mm F/3.5-5.6G VR. After a shooting with the 24-120mm F/3.5-5.6G, it quickly became clear that this one simply was not capable of showing the maximum quality possible with the D600, so both lenses were put through controlled tests to verify this observation.

Even before seeing the files, it was obvious that there was some major softness introduced by the slower lens. Psychic powers? No, file sizes! Recall that image compression reduces more files with fewer details. Take a look at the sizes of identical images taken at 24mm with each lens:

On the left the ones from the 24-120mm starting with F/3.5 and going down to F/22. The file with 10.7MB corresponds to F/8 which means that file has the most details overall. Upon visual inspection, it is not so absolute since this lens shows maximum sharpness in its center at F/5.6 and along edges at F/9.5. F/8 as it would be is smack in the middle.

As for the 24-70mm which starts at F/2.8 and also goes down to F/22, it clearly starts with a non-trivial lead in details-per-image. At F/3.5, there is a difference of 0.8MB. The maximum details corresponds to F/6.7 because edges sharpen up nicely by then. The center is always perfectly sharp with the 24-70mm F/2.8, making it a great choice when shooting wide-open.

Lets see how this looks onscreen:

Even though it starts brighter than the 24-120mm, the 24-70mm is ultra-sharp from F/2.8. In comparison, the 24-120mm gets close by F/5.6 which is 2 stops down, either forcing it shoot at lower shutter-speeds or raise the ISO and incur more image noise. The edges start with a more dramatic difference and they both reach the sharpest point around F/9.5.

Keep in mind that this is the wide-angle performance and things are actually worse at 70mm, the telephoto end of the brighter lens. There, the optimal resolution at the center is reached at F/6.7 for the 24-70mm and F/9.5 for the other lens. The optimal resolution at the edges is reached at F/9.5 for the 24-70mm and F/13 for the 24-120mm and still shows a clear advantage to the former lens.

In summary, if one does not spend on sufficiently good lenses, the performance advantage of a higher-end camera quickly disappears. This is proportional to resolution and those going for a 36 megapixels Nikon D800E instead need to be even more critical of lens performance. In contest, shooting full 1080p HD video only uses 2 MP of resolution, making most lenses much more usable.

• Digital Camera
• Lens