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# Spectroscopic throughput

**Spectroscopic Throughput**

All throughput measurements are based on observations of spectrophotometric standards, collected under photometric conditions. Throughputs are defined as follows:

T(λ) = |
N
_{d}(λ) N_{t} (λ) |

where: * N _{d}(λ) * is the number of photons detected with wavelength λ and

*N*is the number of photons of the same wavelength hitting the telescope's primary mirror. The latter is given by:

_{t}(λ) N _{t}(λ) = N_{*}(λ) 10 ^{(-0.4 μ Aλ) } |

where *N _{*}(λ)* is the star's photon flux at wavelength λ above Earth's atmosphere, in number of photons/cm

^{2}/s,

*μ*is the airmass, and

*A*is a mean monochromatic extinction coefficient.

_{λ}
*The numbers available below are average values,
that do not account for throughput variations as a function of grating
angle. *

Instrument | Gratings | Latest Throughput | All measurements |

NIFS | ZJHK | 20151116 | ZJHK |