Spectra L200 Neon Calibration Test

Initial calibration and testing of a Spectra L200 spectroscope using the integrated neon calibration lamp. The analysis was undertaken using “BASS”. Click “Continue reading” below to see the entire analysis.



Telescope: DSI RC14C (0.35m, f/7 Ritchey–Chrétien)
Imaging Camera: Atik314L+ (1392×1040, 0.65µm)
Spectroscope: Spectra-L200 with 600 l/mm diffraction grating


Images of the Spectra L200 integrated neon lap were taken at a variety of exposures from 1 to 5 seconds. Figure 1 shows the neon calibration lamp centred at approximately 6150 Angstroms. The exposure is 5 seconds at Bin2, with the slit adjusted to approximately 25 microns on the slit adjustment dial.


Figure 1: The appearance of the RAW fits file from the Atik314L+ imaging camera.

Camera angle has been [incorrectly] adjusted to present ‘vertical’ lines. The residual tilt is evident.


1.    Raw profile

An active binning area covering the central portion of the image was selected:


Figure 2 shows the resulting uncalibrated spectral profile as it appears in BASS (click to enlarge image).


Figure 2: Uncalibrated neon spectral profile.

2.    Calibrated profile

Figure 3 shows the result of a simple two point (linear) calibration and provides the following values:

  • Dispersion = 1.08 Å/pixel.
  • Average FWHM = 2.18
  • R = 2818 @ 6143.06Å

Figure 3: Two point linear calibration.

Direct measurement of a number of other lines shows results that are within 0.2 Å of published values.

Figure 4 shows the result of calibration using 6 points and a quadratic fit. The resulting RMS is 0.0878.


Figure 4: Multi-point calibration.

Measurement of additional lines shows improved results over that of the two point calibration, yielding values that are within 0.025 Å of published values.

BASS Measurement Tool

The BASS measurement tool allows easy selecting and measuring of features in a profile. The typical output appears as follows:

Profile                        : CCD Image 41.fit
Selected Start           : 6258.2Å (430.07 px)
Selected End             : 6273.9Å (444.56 px)
Selected Width         : 15.7Å (14.49 px)
Max Flux                   : 26582.7 at 6266.6Å (437.82 px)
Min Flux                   : 400.79 at 6258.21Å (430.07 px)
Flux Range               : 26181.91
Average Flux            : 3797.6 (RMS 8084.89)
Std Deviation           : 7137.49
SNR                            : 0.53
Continuum Slope     : 25.1 ADU/Å  0.27 ADU/px
FWHM                      : 2.11 Å (R = 2971 @6266.6Å)

Formatted Profile

Figure 5 shows a formatted profile produced in BASS. A synthesised colour image strip featuring the neon emission lines appears below the profile.


Figure 5: Formatted neon spectral profile in BASS.


This entry was posted in Spectroscopy. Bookmark the permalink.