Shelyak Lhires III Spectroscope

The ideal input is F/10, which suits Schmidt-Cassegrain telescopes; the manual gives f/8 to f/12 as acceptable. Refractors and Newtonians slower than f/8 can be used, and faster telescopes can use a Barlow lens if the back focus allows.

Yes. The rotation of Jupiter or Saturn is an educational Doppler project. By orienting the slit along Jupiter's equator, you capture the spectrum from both the approaching (blue-shifted) and receding (red-shifted) limbs of the planet. This causes the solar absorption lines reflected from the planet's atmosphere to appear tilted, and the degree of tilt is a direct measurement of the rotational velocity.

You need a C-mount guide camera (not supplied) and autoguiding software. The guide port is a dual-lens C-mount port (0.8x) with 17.5 mm back focus, and the mirror slit sends the field around the slit to it, so the star can be held in the slit.

The Lhires III includes a standard adapter for ATIK cameras, which have a 13 mm mechanical back focus. For other cameras, Shelyak offers adapter sets for 17, 23, 25 and 34 mm back focus in its accessories catalogue.

Yes. The Lhires III was designed for the observation of Be stars, and the manual shows a 2D spectrum of Gamma Cas. At R=18,000 you see the shape of the H-alpha emission profile and can follow its changes, a common amateur-professional collaboration topic.

The Lhires III uses a manual micrometer screw to precisely rotate the internal grating. Turning the micrometer changes which part of the spectrum falls onto your camera sensor. This allows you to center any wavelength in the visible range (400 nm to 750 nm), giving you the flexibility to study any specific spectral feature of interest.

The slit width presents a fundamental trade-off between resolution and light throughput.

• Narrower slits (15 µm, 19 µm): Provide the highest spectral resolution but allow less light to pass through. Use them when detail matters most.
• Wider slits (23 µm, 35 µm): Allow more light to reach the sensor, improving the signal-to-noise ratio for fainter targets, at the cost of resolution.

The slit lets you give priority to resolution or brightness.

Yes. The manual says the camera side is an M42 T-ring thread with enough back focus for a DSLR; the brand-specific T-ring is not supplied.

The standard 2400 lines/mm grating provides the maximum resolving power of R=18,000. Optional grating modules (such as 1800, 1200, 600, 300 and 150 l/mm) lower the resolving power and make fainter objects accessible; examples are novae and bright comets. With a 200 mm f/10 telescope (1 hour, S/N 100), limiting magnitudes range from 5.0 with the 2400 grating to 9.2 with the 150 grating.

Calibration involves several steps. First, you must take calibration frames (bias, darks, flats). For wavelength calibration, you use the integrated Neon lamp to take a reference spectrum. Software such as IRIS or VisualSpec then uses the known wavelengths of the Neon emission lines to create a dispersion solution, which converts the pixel positions in your star's spectrum into an accurate wavelength scale in angstroms or nanometers.

In a Littrow spectrograph, the same lens collimates the light onto the grating and focuses the spectrum onto the camera. This removes the separate lenses of Czerny-Turner or Ebert designs, so the Lhires III is compact and economical to produce.