• The Shelyak eShel II Spectroscope design is a collaboration between Shelyak, Christian Bui, and Michel Pujol.
• The eShel II is an Echelle Spectrograph known for its flawless accuracy and performance.
• Echelle spectrographs disperse parallel light beams using a special grating and focus the dispersed light onto a detector.
• Czerny-Turner spectrographs use collimating mirrors and are preferred for broader wavelength ranges, while Echelle spectographs excel at higher resolution within a shorter wavelength range.
• Echelle spectographs are superior for observing stars and other activities where most of the emission lines and bandpass are focused in one area of the spectrum.
• The eShel II can measure wavelengths between 450 to 700nm with a resolution of >10,000.
• Shelyak has developed the eShel software, an open-source program that controls the various components of the eShel II for spectral line measurement and analysis.
• Spectral recording can be stored and exported using a multi HDU fits file format.

The Shelyak eShel II Spectroscope design is a joint collaboration between Shelyak, Christian Bui, a renowned optic specialist and Michel Pujol who designs Tcl/Tk and AudeLA software applications. These factors combined together make an outstanding Echelle Spectograph design with absolutely flawless accuracy and performance.

Since the eShel II is based on the framework of Echelle spectrographs, it is beneficial to nail down the differences and advantages when compared to other spectrograph models like Czerny-Turner. While the end goals of each are give or take, the same, the way they disperse light and measure it is somewhat different.

• Unlike Czerny-Turner spectrographs which use collimating mirrors to create parallel light beams that can furthermore be dispersed and focused on a mirror, Echelle spectographs use a different type of grating to disperse these parallel light beams which can render better accuracy. A camera lens focuses the dispersed light onto a detector like a camera sensor.
• Compared to Czerny-Turner which generally are preferred for broader wavelength ranges (for instances, measuring Near IR to visible), Echelle versions instead excel at higher resolution of spectral lines and measurements within a somewhat shorter wavelength range making them far superior for observing stars or other activity whereas most of the emission lines and bandpass are focused in one area of the spectrum. This also prevents less instances of overlapping of spectral lines which could cause inaccurate data at longer wavelengths. In the case of eShell II, spectral gratings are >20.

Using the main eShel II, anything between 450 to 700nm can be measured with an >10,000 resolution (measured with an ATIK 460). The spectral domain is also now extended 30-55.

Shelyak eShell II used in conjuction with an 8" SCT, Canon 40D at 9 x 300 s showing the H-Alpha line emphasized in emission near the mid top right.

Shelyak has developed the eShel software which is an open source based program that can control the various components of the eShell II such as the calibration and injection to measure and analyze spectral lines. Following this, with a multi HDU fits file, spectral recording can be stored and exported.

Calibrated recorded spectral analysis of Beta Persei between H-Beta and H-Alpha using the eShel software.

• Fiber injection and guiding unit
• Calibration unit
• Echelle spectroscope
• eShel Software

Beta Lyr – Shelyak [:-)] & P Cygni – 7 x 300 s 8′ SCT

WR 140 and Nova Del 2013 1x600s 14′ SCT and ATIK 460EX bin 2×2

Here is also a good exemple of echelle spectroscopy with an animation of raw images of BW Vul, a pulsating star. 5min expoures, 60cm f/3.5 telescope at pic du Midi; QSI 516s camera.

Here is a spectrogram of BW Vul around Sodium doublet.

• The Shelyak calibration unit, although designed for the eShel II, is compatible with most fiber-based Echelle spectroscopes.
• The calibration unit utilizes a Thorium-Argon lamp with high voltage power to align and prepare light paths for dispersion. It serves as a baseline for spectral analysis.
• A flat lamp is used in the calibration unit to aid in order geometry and blaze processing, optimizing the performance of the spectrograph.
• An LED light source is included to verify the orders of calibration, ensuring proper functioning and accurate measurements.
• The module can be controlled using Audela software and RS-232, allowing for easy management and adjustment of the injection unit and other components.

While intended for eShell II, this Shelyak calibration unit is compatible with most fibre based Echelle specroscopes. To make sure the light paths are properly aligned and prepared for dispersion, the calibration unit serves as a method to ensure this is done by using a Thorium-Argon lamp (that covers the visible spectrum) with high voltage power to ensure proper alignment of light beams. This essentially functions as a baseline for spectral analysis.

A secondary source of light from the calibration unit is a flat lamp order geometry and blaze processing. Since blaze processing typically refers to how the blaze function is processed in which light is dispersed through grating, it can help fine tune the eShel to make sure measurements are intact. This is absolutely crucial for accurate information to be rendered and processed.

The third source of light is an LED which furthermore verifies the orders of a calibration to ensure the unit is functioning and measuring properly.

Using an RS-232, the module can be controlled via Audela software as well as the mirror of the injection unit.

The image above shows the spectrum for the Thorium-Argon lamp which serves as a blueprint to ensure spectral emissions areas are recorded properly.

In order for the eShel to measure the target light source flow, also known as flux accordingly, the fiber injection and guiding unit must be used so the photons enter the 50 μm optical fiber. In conjuction with an autoguider camera (sold separately) that can center the object in the field of view. Another benefit it serves is connecting the lights from the calibration unit with a 200 μm optical fibre with a switch available to alter from one source to another.

• f/6 telescope input is the standard configuration. Possibility to add the F/7.8 and F/9 configuration
• Chromium mirror with 50µm hole
• Object FC connector
• Calibration FC connector
• Mirror switch to bring calibration light into object fibre
• Connection with guiding camera : C mount
• Operating temperature of the guiding unit : -25° C to +30° C
• Guiding and injection unit storage : -30° C to +40° C
• 2 inch nosepiece & T-mount thread

• M42 T adapter telescope interface
• Backfocus ~45mm
• Miror with light going through a 50µm hole for the f/6 standard version
• Calibration fiber input (remote controlled mirror position)
• Fiber object 50 µm, 5, 10 or 20 meters length
• Calibration fiber 200 µm, 10 or 20 meters length
• Fibers protected by metal/plastic casing
• FC fiber connectors
• C-mount for guiding camera (sold separately)

For users who have a Celestron or Meade SCT and want to connect an eShel, Alpy 600, or LISA Spectrograph, this adapter set (SCT to M42 consiting of two parts) will enable the connection of these to these optical tubes, usually along with a focal reducer for wider field measurements.

The optical fiber is the connection tool that facilitates the beam of light being emitted from the telescope optics to the spectroscope to ensure light if fully collected (with virtually negligible light loss) before being dispersed. The optical fibers designed by Shelyak are tailored specifically for eShel spectrograph and is a necessary component for it to function.

• The Shelyak Optical Fiber is is a multimode format which means that unlike single mode fibers, they can simultanously faciliate multiple light paths due to their larger inner size diameter which allows more photos to travel.
• 50μm core for optical and 200μm for calibration diameter.
• The outer material of the fiber is composed of tubing to ensure stable connection.
• FC connectors at each end.