The transmission curves of the narrowband filters at T = 77 K and for an incidence angle of θ = 5° have been calculated from the measured data (T = 293 K, θ = 0°).
First, the temperature-related shift of the central wavelength (CWL) per Kelvin given by the manufacturer (see the narrowband filter table) was used, leading to a blueshift of the transmission curve. Then the effect of the tilt (θ = 5°) onto the CWL was taken into account by

where n = 2 is the effective refractive index of the interference filters, see also Ghinassi et al. 2002, A&A 386, 1157 and references therein.

An increase in transmission of about ~6-8% is expected for the filters at T = 77 K, which has not been taken into account in the calculation.