FLPhotoCatcher wrote:So, the telescope, "is optimized for the infrared exploration..." Does this mean that it will be able to take visible light images? If not, why not? It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.
It has a camera that has some sensitivity at the red end of the spectrum, so in a sense it can take "visible light" images. For instance, it has sensitivity to H-alpha at 656 nm, but has no narrowband filters for this line.
The wavelength range for the JWST is much wider than that of any visible light instrument (such as Hubble). The primary reason that it is limited to wavelengths longer than 600 nm (and thus largely outside the visible range) is because of the nature of the detectors used in the cameras. Ordinary silicon detectors such as those used by Hubble (and in our everyday digital cameras) are not sensitive outside of visible and very near IR. So a near- to mid-range IR sensor is made of more exotic materials, not sensitive to visible light. In order for the JWST to image visible light, they would have needed another camera. Perhaps they would have considered this, except for the fact that all the other optics, including the main mirror, are made of materials that are not well suited to reflecting or passing shorter wave light. Nor is the adaptive optics system well suited to short wavelengths.
In short, it just isn't practical to make a single instrument that covers the range from short wavelength visible through mid-IR, because all of the manipulation and detection technology is different. It's like saying that your radio should also serve as a microscope. Sure, both detect and manipulate electromagnetic radiation. But they do so very differently.