Both are made of high quality fused silica with fused silica cladding doped to increase its index of refraction and keep the light contained within the core. These fibers are useful well into the UV, the short wavelength limit depending on how long the fibers are. Unfortunately, they have absorption bands in the IR, with a significant reduction in throughput over a narrow band between 700-730nm.
All fibers increase the solid angle of slow beams to some extent.
The Effect of Seeing The seeing and accuracy of the fiber positioning further affects the amount of light falling into the fiber. Sometime during 2000, CTIO Hydra is expected to be equipped with changeable slit masks which will be placed in front of the fibers so that spectral resolution can be maintained even under conditions of less than ideal seeing. This Fiber attenuation graph was measured at CTIO on the Hydra fibers and shows that the attenuation is acceptable at all wavelengths over the spectrograph's design wavelength range from 330-1100nm. The short wavelength limit is determined by the UV cutoff of the glasses used in the ADC corrector. The long wavelength limit is set by the limit of useful sensitivity of silicon CCDs.