Chroma High-T R-Bessell 50 mm Unmounted Photometric Filter is designed for precise brightness measurements of astronomical objects in the R band of the Bessell UBVRI system. It transmits a broad range of the red spectral region, enabling standardised photometric observations with CCD and CMOS cameras.
The filter profile was developed for photometry performed with electronic detectors. Combined with U-Bessell, B-Bessell, V-Bessell and I-Bessell filters, it can be used to produce multi-band light curves, determine colour indices and compare observations with data obtained in the standard UBVRI system.
The R-Bessell filter has a central wavelength of approximately 645 nm and covers a broad spectral range, approximately from 550 to 800 nm. It can be used for observations of variable stars, exoplanet transits, supernovae, star clusters and other objects requiring repeatable and comparable photometric measurements.
Durable magnetron-sputtered coatings are applied to a single substrate made from high-quality optical glass. The primary filtering coatings are deposited on the front surface, while the rear surface receives an anti-reflection coating that reduces glare and ghost images. The construction maintains spectral stability during changes in temperature and humidity.
The round filter has a diameter of 50 mm and a thickness of 3 mm and is supplied without a cell, allowing it to be installed in a compatible filter wheel or holder. Its blackened glass edge reduces internal reflections, while surface accuracy of λ/4 or better helps preserve image quality. The filter is designed for optical systems operating at f/4 or slower.
• photometric R band of the Bessell UBVRI system
• high-transmission High-T version
• central wavelength of approximately 645 nm
• operation in the red spectral region
• approximate transmission range from 550 to 800 nm
• construction designed for CCD and CMOS photometry
• suitability for standardised brightness and colour measurements
• durable magnetron-sputtered coatings
• rear anti-reflection coating reducing glare
• spectral stability during changes in temperature and humidity
• blackened edge reducing internal reflections
• round 50 mm format designed for filter wheels
• construction designed for f/4 and slower optical systems
• 50 mm diameter unmounted Chroma High-T R-Bessell filter
• manufacturer: Chroma Technology Corp.
• manufacturer code: CT-27053-50D
• series: High-T Bessell
• filter type: photometric
• photometric system: Bessell UBVRI
• band: R-Bessell
• spectral region: red
• central wavelength: approximately 645 nm
• approximate transmission range: 550–800 nm
• shape: round
• diameter: 50 mm
• glass thickness: 3.0 mm
• cell: none
• coating technology: durable magnetron-sputtered coatings
• rear-surface coating: anti-reflection
• optical surface accuracy: λ/4 or better
• edge finish: blackened
• recommended optical speed: f/4 or slower
• application: CCD and CMOS astronomical photometry
