Remarks on a Johann spectrometer for exotic-atom research and more

• Ultimate-resolution highly stable Johann spectrometer with excellent peak/background ratio
• Detailed Monte-Carlo studies and rules of thumb for quick assessment of experimental needs
• Performance demonstrated with novel results in exotic-atom and fluorescence X-ray experiments.

General properties of a Johann-type spectrometer equipped with spherically bent crystals are described leading to simple rules of thumb for practical use. They are verified by comparing with results from Monte-Carlo studies and demonstrated by selected measurements in exotic-atom and X-ray fluorescence research.