Releasing the data of MTF Chart: Diffraction MTF and Geometrical MTF

SIGMA CORPORATION releases MTF (Modulation Transfer Function) Chart as one of the measurements that evaluates a lens’ performance on the official website.
However, the specific data does not have an official way to display or calculate, and it is known that the value will change drastically depending on whether or not it considers diffraction quality of lights.
We have been striving to accurately communicate lens’ performance to end-users as one of the measurements for their product choices by releasing our lens’ optical performances. From now on, we are going to release “Geometrical MTF” Chart in addition to “Diffraction MTF” starting from the new products that we announce this time.*

On our official website, we also have Distortion and Vignetting data which can also be the measurements for a lens’ performance. Please refer to them as well.

* For existing line-ups, we are planning to release the data within March 2014.

MTF Chart

There are two types of MTF chart. One considers the diffraction quality of light, which is called “Diffraction MTF”, and the other, “Geometrical MTF” does not.

The quality of light appears in the diffracted light, and becomes more distinct as the F value gets bigger, resulting in lower image quality. Also, diffracted light exists at every aperture, which is why Sigma has been releasing Diffraction MTF data from the beginning since it is very close to the actual image data.
The advantage of using “Geometric MTF” data is that it is easy to measure and calculate since it does not consider the diffraction quality of light, yet it tends to show higher values in the graph than actual images.