Stack tests with a 1.5 A filter


1) Center Wave Length (CWL) and bandpass (FWHM) as a function of the F/D ratio of the telescope and of the tilt of the F-P filter (collimated beam, telecentric beam, non-optimized telecentric system)

2) CWL shift and FWHM broadening in non telecentric lens systems

3) Daystar filter modelling and additional results

4) Air-spaced F-P etalon theoritical performances

5) Analysis of the PST modification (air-spaced F-P etalon) and comparison with mica-spaced F-P etalons

6) Contrast factor of the F-P etalon and blocking filter assembly

7) Contrast factor of the F-P etalon : test of various stacking schemes

8) Fabry-Perot math and bibliography


Acquisition / processing :

Takahashi TOA150 + TZ-4 + Basler 1920-155.
June 1, 2019.
Good seeing condition for all images : 0.4 to 0.5 arsec measured with the SSM.
Linear visualisation and same threshholds for all images.
No gamma at acquisition nor for processing.
Unsharp mask. No local processing.

Transmission factor of the 1.5 A filter :

2.5 factor between with / without 1.5 A stack  measured with the SolarSpectrum RG 0.3A.

If both filters were perfect one-cavity etalons, the ratio between the 0.3A and the 0.3A + 1.5A would be x1.38 transmission factor. Accordingly, the peak transmission of the 1.5 A filter  is estimated to 1.38 /2.5 = 55%, which seems realistic.

Daystar PE 0.6A (left) versus  Daystar PE 0.6A + 1.5 A filter (right) :

The benefit of the stack with the 1.5 A filter  is obvious. 

Daystar PE 0.6A + 1.5 A filter (left) versus SolarSpectrum RG 0.3 A (right)

The 0.6 A + 1.5 A stack is clearly better than the 0.3 A single stack.

SolarSpectrum RG 0.3 A (left) versus SolarSpectrum RG 0.3 A + 1.5 A filter (right)

 Once again, the stack with the 1.5 A filter gives a big boast to the contrast (i.e. better Ha line separation).

Daystar PE 0.6A + 1.5 A filter (left) versus SolarSpectrum  0.3 A + 1.5 A filter (right)

Flat comparison

All flats are normalized to same average and displayed with same thresholds.


SolarSpectrum RG 0.3A
SolarSpectrum RG 0.3A + 1.5A filter
SolarSpectrum n°2 0.3A
SolarSpectrum n°2 0.3A + 1.5A filter
 DayStar 0.4A
DayStar 0.4A + 1.5A

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