Overall results

	Test method	f-ratio	Surface sampled	FSR	Gap	raw FWHM	deconvoluted FWHM	Delta CWL	Note
Lunt 40 gen 1 (bought second-hand in 2024)	Interferometry with hydrogen lamp	collimated	full aperture	13.0 A	0.16 mm	0.70 A	0.65 A	+ 0.09 A	Front etalon of a 40 mm Lunt refractor

The transmission curve of the etalon is a textbook Lorentzian.
raw FWHM = etalon FWHM convoluted by hydrogen lamp FWHM

Measurement of the etalon by interferometry using a hydrogen lamp in diffuse light

Principe: the Fabry-Perot cavity is used as a Fabry-Perot interferometer

Optical setup: Hydrogen lamp => diffuser => etalon => Nikon Z7II with 85 mmS f/1.8 lens


Interference fringe pattern

Lunt LS40 gen1 - Interference fringe pattern - Nikon Z7II - 85 mm S f/1.8 Nikkor lens at f/1.8 - 12-bit RAW file - 1 s - 100 ISO - 11 May 2024

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