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Shelyak Grating module for the Lhires III - 1200 l/mm

Shelyak Grating module for the Lhires III - 1200 l/mm

by Shelyak
SKU SHK-SE0006
CA$1,099.00 - CA$1,099.00
CA$1,099.00
CA$1,099.00 - CA$1,099.00
CA$1,099.00
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  • 1200 lines/mm Grating
  • Direct-Fit Module for Lhires III
  • Expands Spectrograph Wavelength Coverage
  • Ideal for Spectroscopic Surveys
  • Interchangeable with Standard Grating
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Grating module for the Lhires III - 1200 l/mm

    Swap the standard 2400 l/mm grating in your Shelyak Lhires III spectrograph for this 1200 lines/mm module to trade high resolution for significantly broader spectral coverage in a single exposure. This module suits observers who want to follow broad spectral features of bright stars and bright novae over a wider window per exposure.

    The 1200 l/mm Trade-Off: Broader Wavelength Coverage at Lower Resolution

    In spectroscopy, a grating's line density dictates the trade-off between spectral resolution and wavelength coverage. A higher line count, like the Lhires III's standard 2400 l/mm grating, spreads the light out more, delivering higher resolution over a smaller spectral window. This 1200 l/mm grating does the opposite; with fewer lines, it produces a less dispersed spectrum, allowing a much wider range of wavelengths to fall onto your sensor in a single frame.

    This capability is critical for survey work, initial classification of variable stars, or capturing the full profile of objects with broad emission lines. Each exposure covers about three times more of the spectrum than with the 2400 l/mm grating (about 25 nm against 8.5 nm in Shelyak's reference setup), so far fewer exposures are needed to cover the visible range, saving valuable observing time.

    1200 l/mm vs. 2400 l/mm: Choosing the Right Grating for Your Target

    The standard 2400 l/mm grating is the correct tool for the high-resolution work the Lhires III is famous for—measuring precise radial velocities, studying detailed line profiles of Be stars, or resolving close binary systems spectroscopically. It prioritizes detail over breadth.

    The 1200 l/mm grating module suits work where a wider spectral window matters more than the highest resolution, while still giving a resolving power of about 5900 at H-alpha. It is a good choice for:

    • Bright Nova Spectroscopy: Following broad hydrogen emission lines over a wider window than the 2400 l/mm grating gives, while the nova stays bright.
    • Fainter Stars: Reaching a limiting magnitude of 6.8, against 5.0 with the 2400 l/mm grating (Shelyak's Lhires III table: 200 mm f/10 telescope, 1 h exposure, S/N 100).

  • Why would I choose the 1200 l/mm grating for my Lhires III over the standard 2400 l/mm?

    You would choose the 1200 l/mm grating when your primary goal is to capture the widest possible range of wavelengths in a single exposure. The standard 2400 l/mm grating provides higher resolution but covers a much narrower spectral window. With a resolving power of about 5900 at H-alpha (17 km/s in radial velocity), it still records useful line detail.

    What is the main advantage of a lower-resolution grating like this 1200 l/mm module for the Lhires III?

    The main advantage is efficiency. For bright stars and bright novae, important spectral features can be spread far apart. The 1200 l/mm grating covers about three times more of the spectrum per exposure than the 2400 l/mm, so a mosaic needs far fewer frames, saving time and simplifying data acquisition.

    Is the 1200 l/mm grating module difficult to install in the Lhires III?

    No, the Lhires III is designed for interchangeable grating modules. The process involves opening the access panel and carefully swapping the existing module with the new one. Always refer to your Lhires III manual for the specific procedure to avoid damaging the delicate grating surface.

    If I want to study the H-alpha line profile of Vega (Alpha Lyrae) with my Lhires III, is the 1200 l/mm grating the right choice?

    No. For detailed analysis of a single, narrow spectral line like H-alpha, the standard 2400 l/mm grating is the correct tool. Its higher resolution is necessary to reveal subtle shifts and profile changes. The 1200 l/mm grating also records the line profile, with a resolving power of about 5900 against 17,000 for the 2400 l/mm in Shelyak's table, so with less detail.

    Does using the 1200 l/mm grating module change the calibration process for the Lhires III?

    Yes, absolutely. You must perform a new spectral calibration after installing the 1200 l/mm grating. The dispersion (angstroms per pixel) is different from the 2400 l/mm grating, so your previous calibration files will no longer be accurate. You will need to create and save a new calibration profile for this specific setup.

  • Grating Density 1200 lines/mm
    Compatibility Shelyak Lhires III Spectrograph
    Application Resolving power about 5900 (H-alpha), wider spectral window than the 2400 l/mm
    Resolving power (R) About 5900 (H-alpha)

    • 1200 l/mm Grating Module for Lhires III

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