Introduction

This is yet another resolution comparison of three lenses. In this exercise, photographs were taken, tripod mounted, of a Koren 2003 target. All photos were taken with a Nikon D100 in NEF (RAW) mode. Lenses were each set at 70mm focal lengths and with apertures of f/5.6. The NEF files were each saved as JPEG files using the maximum quality factor (12 in Photoshop). No additional PhotoShop processing was undertaken. The JPEG files were analysed using the ImageJ freeware Java-based analysis package.

Target

Here is the Koren 2003 target. The yellow line represents the band upon which the analysis curves are based. This band is a sine-wave variant which spans between full black and full white. Subtleties in the imaging resolution capabilities are best revealed in this band (as opposed to the square wave band).

Data + Analysis

The ImageJ software provides for a means to make image-based, pixel densitometer measurements. No absolute distance scale has been maintained (i.e., no attempt was made to obtain absolute MTF and LPI measurements). The results below provide only a relative comparison.

The X-axis is a normalized, relative, scale. Since each photo was taken from the same distance, focal length and aperture, valid comparisons may be made. The Y-axis gives a measure of grey-value; with 0 indicating absolute black and 255 indicating absolute white. Ideally, in these graphs, a better lens will retain a strong shoulder-to-shoulder character moving from left to right (i.e., from lower to higher resolution). The more rectangular this character is, the better the resolution capability.

Results

The most expensive lens of the bunch is the Nikkor, shown in the upper left. It retains a strong contrast at increasing reloutions and holds it's rectangular shape best.

The least expensive of the three lenses compared here is the Sigma, shown in the upper right. At f/5.6 and 70mm, this lens is at it's widest aperture. The results exhibit a triangular fall-off pattern across increasing resolution indicating a degredation of contrast with higher resolutions. This would mean that dark-light contrasts are diminishing with increasing photographic detail. Tack-sharp photographs would be a greater challenge for this lens in a wide-open state.

Two sets of Tamron results are shown. At lower left are Tamron's results at f/5.6 which can be compared to the preceding Nikkor and Sigma results. The Tamron's resolution capability generally falls between the Sigma and the Nikkor. The triangular fall-off is less evident than was seen with the Sigma lens, and yet it is unable to retain the Nikkor's example of strong, rectangular contrast character for increasing resolutions.

The results for the Tamron at f/11 are not significantly different, thus indicating that smaller apertures may not help to improve resolution characteristics, as the author of this web page once believed was true.

Last updated: August 24, 2003

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