Final answer:
Image-orthicon TV cameras are not widely used due to their 1. high cost, sensitive nature requiring shielding from magnetic signals, and very fast discharge time, which are not suited for modern imaging requirements.
Step-by-step explanation:
Image-orthicon TV cameras are not widely used due to several factors that are no longer compatible with modern requirements for broadcasting and imaging technology. In particular, they have been succeeded by more advanced technologies that offer better performance and more practical features. The high cost of Image-orthicon cameras, as well as the need for significant shielding from magnetic signals due to sensitivity issues, have contributed to their obsolescence.
Additionally, these cameras are not as versatile as modern digital sensors that allow long exposure times critical for capturing faint objects in astronomical observations. Unlike modern digital sensors used in astrophotography that can continuously integrate light over an extended period to collect faint signals, the Image-orthicon had a very fast discharge time, making it less suitable for modern applications that require high-quality imaging across various conditions.