The new Sigma 18-250mm f/3.5-6.3 DC Macro OS HSM lens is the first lens to use Thermally Stable Composite (TSC), meaning that tighter construction using thinner and lighter materials can be achieved. Read more in the Sigma 18-250mm f/3.5-6.3 news story.
Sigma 18-250mm f/3.5-6.3 DC Macro OS HSM Performance
How to read our charts:
The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column.
The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple.
Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.
Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.