Observational redshift from general spherically symmetric black holes Diego A. Martínez-Valera, Mehrab Momennia and Alfredo Herrera-Aguilar Eur. Phys. J. C, 84 3 (2024) 288 Published online: 20 March 2024 DOI: 10.1140/epjc/s10052-024-12649-1