Color correction in optical systems or why optical design needs fluoro-phosphate glasses
Dr. Ralf Jedamzik, Application Manager, SCHOTT Advanced Optics
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 2
Optical glasses are mainly categorized according to their refractive index and Abbe number
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 3
The refractive index n is a measure for the deflection of light in transition to a different medium
air n1
The world of optical glass glass
n2
n = 1.487 sin() n2 n = 2.02 sin( ) n1
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 4
The Abbe number is a measure for the change of refractive index with the wavelength (dispersion)
Refractive index
1.53
n n F C nd
1.51
nd 1 d 1.49 nF nC 0.3 0.4 0.5 0.6 0.7 0.8 The higher the Abbe number the lower the dispersion wavelength in µm
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 5
Refraction of different glasses as seen with a prism
Flint glasses: high refractive index + high dispersion
Crown glasses: low refractive index + low dispersion
N-FK58 XLD
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 6
Chromatic aberration: color fringes in high resolution lens systems (example tele zoom lens)
Chromatic aberration show stopper for high resolution optics
Color correction in optical systems, Dr. Ralf Jedamzik, May 2014 © SCHOTT AG SCHOTT Advanced Optics Color correction in optical systems 7
Chromatic aberration of a single lens: „blue refraction ( B) is stronger than red refraction ( R)“