- The interference patern is quite uniform with fringes having textbook Lorentzian profile.
- The mesurements from the different rings are very consistent.
- Results from 38 mm to 21 mm aperture are quite similar.

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Peak transmission

Optical setup: Sun => C8 EdgeHD => f/35 telecentric => etalon => Solex with 7 microns x 6 mm slit, fc = f i =200 mm, 2400 l/mm grating, IMX585, 0.0471 A/pixel dispersion
10 May 2025 - Sun elevation = 41°


Comparison of the intensity of the lines of the solar spectrum with / without etalon allows to estimate the peak transmissionn to about 68% at f/35 (without the ERF). 
It is difficult to estimate the uncertainty of the measurement.The spectra without/with the etalon were taken at 20 min interval. Sky transparency might have changed in between.

By comparison, a second etalon without ERF was measured 15 min before at 59% without the ERF. This is consistent with the 10% absorption of the RG630 with 3 mm thickness.