A novel optical design
VISTA’s primary mirror must have a large light-collecting area so that it can detect faint objects. But to be able to image wide areas of sky as rapidly as possible, VISTA’s overall optical system must also cover a much larger angle of view than a standard telescope. It is not easy to obtain good image quality with such a large primary mirror and wide field because the further the incident light is from being parallel to the optical axis of the telescope, the harder it is to form a sharp image. Therefore a completely novel optical design was introduced for VISTA. Professor Emerson summarizes the main features as follows: “The reflecting telescope alone does not produce high-quality images. These are created with the help of a camera, which means that the two instruments cannot be used independently from one another. The telescope and camera are optimized as a single instrument. The camera corrects the optical distortions towards the edge of the field of view that would unavoidably occur if only the secondary and primary mirrors were involved.”
Primary mirror and infrared camera are both extraordinary
New astronomical findings in the infrared range
The images that can be produced by this unusual design will each cover an area of approximately 0.4 square degrees of sky, which is equivalent to about twice the size of the full moon. The image quality will be so good that exposures will even include stars and galaxies that are 10 to 100 times fainter than those previously registered in such sky surveys. Scientists thus expect to answer many astronomical questions, whereby the main focus will be on investigations that can only be conducted in the infrared region of the spectrum. One example is, for instance, observing the birth of a star. New stars form from clouds of gas and dust that are usually impervious to visible light, but not to infrared emission. Infrared images are also a prerequisite for investigating distant galaxies because the farther away they are, the more the emission of the galaxy shifts from the visible to the longer wavelengths of the infrared region of the spectrum.
In fact many believe that VISTA will lead to completely unprecedented discoveries. Professor Emerson: “This has always been the case when astronomers had a new top-quality telescope with a totally different design. We are convinced that VISTA will be no exception.”