Filters for scientific photometry: The UBVRI system was developed in the 1950s for the 0.9 m telescope at McDonald Observatory and initially consisted of a set of UBV filters according to Johnson. It was later expanded by Cousins to include R and I filters in the red region of the spectrum. The filters of the extended UBVRI system according to Johnson and Cousins include:
- U – ultraviolet, with a transmission window between approximately 320 and 400 nm
- B – Blue, with a transmission window between approximately 400 and 500 nm
- V – Visible, i.e. visible light, with a transmission window between approximately 500 and 700 nm
- R – Red, with a transmission window between approximately 550 and 800 nm
- I – Infrared, with a transmission window between approximately 700 nm and 900 nm.
