Quality

Sharpness and contrast

Let’s have a look at the theoretical performance (MTF-charts) of the Sigma 150-500 OS first.

MTF of the Sigma 150-500/5-6.3 DG OS HSM
The Sigma 150-500/5-6.3 OS at 150mm, f5.0		The Sigma 150-500/5-6.3 OS at 500mm, f6.3

These charts show the lens-performance at the largest aperture, in this case for f5.0 (at 150mm, resp. f6.3 at 500mm). Higher values are better and the closer the dotted and the continuous lines of each color are together the less astigmatism (= resolution depends on the orientation of the test-pattern) the lens has. The x-axis displays the distance from the optical axis (=center of the sensor) in mm. I’ll show you the real-life performance at 4 mm (center), 13 mm (DX-corner), and 20 mm (FX-corner) on a D800 in a moment.

The charts above imply that the lens should have a pretty good overall contrast. But it also shows that regarding sharpness it either has a problem outside the DX image-circle on the short end or a general problem with astigmatism at the long end. Let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars.

What follows are near-center results (first column) followed by DX-corner results and FX-corner results on a D800. The D800 results from the DX-corner should be a very good approximation for performance on a 16MP DX sensor (like the D7000), because the pixel-pitch of both sensors are the same. But differences in the AA-filter and micro-lens-design of a D800 and a D7000 might yield different end-results.

Processing was done in Lightroom 4 from RAW at camera standard settings. This is a deviation from my earliest reviews which were developed in CaptureNX 2. This was triggered by a close comparison of both RAW-converters: Lightroom 4 has a sharpening algorithm that can be better tuned for small details. Noise-reduction is set to 0, sharpening to 70/0.5/36/10, with no extra tone, color, or saturation-adjustment. White-balance was adjusted to a neutral white and I did some exposure compensation to make the brightness match. Removal of standard (tangential) CA is ON, for longitudinal CA OFF.

These are all 100% crops!

First are the results from 150mm focal length:

Sigma 150-500/5-6.3 OS at 150mm with Nikon D800 100% crop from center		Sigma 150-500/5-6.3 OS at 150mm with Nikon D800 100% crop from DX-corner		Sigma 150-500/5-6.3 OS at 150mm with Nikon D800 100% crop from FX-corner
f5, 200 ISO		f5, 200 ISO		f5, 200 ISO
f5.6, 200 ISO		f5.6, 200 ISO		f5.6, 200 ISO
f8, 200 ISO		f8, 200 ISO		f8, 200 ISO
f11, 200 ISO		f11, 200 ISO		f11, 200 ISO
f16, 200 ISO		f16, 200 ISO		f16, 200 ISO

This is quite an astonishing performance for a zoom: even wide open the results are very good at the center, the DX-corner, and the FX-corner. Remember that we are looking with a 36MP sensor at the performance of this lens. So this is an excellent result!

Now let’s see whether the lens can keep this level of performance at 200mm too:

Sigma 150-500/5-6.3 OS at 200mm with Nikon D800 100% crop from center		Sigma 150-500/5-6.3 OS at 200mm with Nikon D800 100% crop from DX-corner		Sigma 150-500/5-6.3 OS at 200mm with Nikon D800 100% crop from FX-corner
f5.3, 200 ISO		f5.3, 200 ISO		f5.3, 200 ISO
f5.6, 200 ISO		f5.6, 200 ISO		f5.6, 200 ISO
f8, 200 ISO		f8, 200 ISO		f8, 200 ISO
f11, 200 ISO		f11, 200 ISO		f11, 200 ISO
f16, 200 ISO		f16, 200 ISO		f16, 200 ISO

Performance in the DX-corner and the FX-corner deteriorates a bit below f8 compared to 150mm. But still the center performs very good already at f 5.3 and corner resolution is not too bad too. At f8 the image quality across the FX sensor has improved to very good levels with the center performing flawlessly. Note: I think the test-shot of the DX-corner at f5.6 may be marred by some residual shake and not show the full potential.

Next up are the results at the 300mm focal length:

Sigma 150-500/5-6.3 OS at 300mm with Nikon D800 100% crop from center		Sigma 150-500/5-6.3 OS at 300mm with Nikon D800 100% crop from DX-corner		Sigma 150-500/5-6.3 OS at 300mm with Nikon D800 100% crop from FX-corner
f6, 200 ISO		f6, 200 ISO		f6, 200 ISO
f8, 200 ISO		f8, 200 ISO		f8, 200 ISO
f11, 200 ISO		f11, 200 ISO		f11, 200 ISO
f16, 200 ISO		f16, 200 ISO		f16, 200 ISO

Center performance is still pretty good already wide open although the corners suffer from low contrast and astigmatism at f6. F8 sharpens up the FX-corner while the center and DX-corner don’t profit equally. F11 gives the center a boost to very good sharpness and the DX-corner get visibly more definition. But even at f16 you can no longer reach the quality of 200 mm focal length at f8.

Next are the results at the 400mm focal length:

Sigma 150-500/5-6.3 OS at 400mm with Nikon D800 100% crop from center		Sigma 150-500/5-6.3 OS at 400mm with Nikon D800 100% crop from DX-corner		Sigma 150-500/5-6.3 OS at 400mm with Nikon D800 100% crop from FX-corner
f6.3, 100 ISO		f6.3, 200 ISO		f6.3, 200 ISO
f8, 100 ISO		f8, 200 ISO		f8, 200 ISO
f11, 100 ISO		f11, 200 ISO		f11, 200 ISO
f16, 100 ISO		f16, 200 ISO		f16, 200 ISO

Good center performance can now only be achieved at f8 but the corners (at DX especially) are suffering from some light-bleeding. And even if you stop down further neither the DX-corner nor the FX-corner achieve good definition. BTW. the deterioration in image quality at f11 from the center into the corners can also be seen at 66% or 50% magnification. So even on a D4 or a D700 the weak corners will show.

And finally at the maximum of 500mm:

Sigma 150-500/5-6.3 OS at 500mm with Nikon D800 100% crop from center		Sigma 150-500/5-6.3 OS at 500mm with Nikon D800 100% crop from DX-corner		Sigma 150-500/5-6.3 OS at 500mm with Nikon D800 100% crop from FX-corner
f6.3, 100 ISO		f6.3, 100 ISO		f6.3, 100 ISO
f8, 100 ISO		f8, 100 ISO		f8, 100 ISO
f11, 100 ISO		f11, 100 ISO		f11, 100 ISO
f16, 100 ISO		f16, 100 ISO		f16, 100 ISO

At the 500mm focal length you need to stop down to f11 to get good center performance. But it seems that the image quality at the DX- or FX-corner is immune to stopping down. But there is still some definition of fine detail even fully open in the corners although everything is covered in a haze.