Quark (chromosphere version) #2

(July 2022)

This Quark is probably one of the first version. More than 5-year old. There is no adapter to use it on 2" focuser.

The filter was measured using the following approach:
- Sol'Ex spectrometer in a f/45.1 telecentric beam (C8 EdgeHD f/10.5 => Quark with its 4.3× telecentric => Sol'Ex),

Filter Test method f-ratio Surface  measured FSR FWHM Bandwith at 10% peak transmission
Quark #2 Sol'Ex spectro
(fc =fi = 125 mm, ASI290, 0.0757 A/px dispersion)
f/45.1 telecentric 10 micron x 4.5 mm 25.4 A
< 0.45 A
1.2 A
(consistent with a FWHM of 0.40 A)

Sol'Ex spectrometer: measurement in a f/45 telecentric beam

Optical setup: Sun =>
Hat 8 telescope => Quark with its 4.3× telecentric beam => Astronomilk Ha 12 nm => Sol'Ex spectrograph

10 microns slit, 125 mm collimating lens, 125 mm imaging lens, ASI290 camera, 12-bit acquisition.
Measured dispersion = 0.0757 A/pixel
Conditions : deep blue sky
2 July 2022

Four succesive images :
- Solar spectrum (= no filter).
- Solar spectrum transmitted by the Quark at ambiant temperature (about 29°C). This spectrum is registered to the solar spectrum.
- Same as above, but different vizualisation thresholds.
Solar spectrum transmitted by the Quark, when tuned to Ha (seems to be close to ambiant temperature. Knob to 6 o-clock position. This spectrum is registered to the solar spectrum.

The FSR is equal to 25.4 A

The transmission profile of the etalon is given by the ratio "transmitted solar spectrum/solar spectrum". The profile was measured at different temperatures from ambiant to tuned to Ha. The results are the same to +/- 0.05 A.


The direct measurement on the graph at 50 % and 10% peak transmission are given on the graphs.
The bandwidth at 10% transmission is consistent with a FWHM = 1.2/3 = 0.40 A.

The profiles were also curve-fitted with Lorentz or Voigt function to improve the accuracy of the FWHM mesurement:

Etalon temperature FWHM (from graph) FWHM curved-fitting Lorentz FWHM curved-fitting Voigt
Ambient 0.49 A 0.39 A 0.45 A
Tuned to Ha 0.45 A 0.39 A 0.45 A

Because of the better fit with the Voigt function, the value considered for FWHM is < 0.45 A (telecentric beam at f/45). This is consistent with a 0.40 A FWHM in collimated beam.

Here is the example with the Quark tuned to Ha line. FWHM obstained by curve-fiiting with a Voigt function is equal to 5.9 pixel × 0.757 A/pixel = 0.45 A

Visual observation

The double limb effect is very limited, which is consistent with a very narrow bandpass.
The transmission is very low (oxydized BF ?)

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