Why do I need the Shelyak 0.63x reducer for spectroscopy with my SCT?
A standard f/10 SCT produces a small, dim image at the focal plane. The Shelyak 0.63x reducer converts this to f/6.3, creating a brighter, more concentrated beam of light. This allows more photons to pass through the narrow slit of your spectrograph per unit of time, significantly boosting your signal and allowing you to capture spectra of fainter objects.
What makes this Shelyak reducer different from a standard Celestron or Meade f/6.3 reducer?
The key difference is the optical design and purpose. Standard reducers are also correctors, designed with 4-element lenses to flatten the field and reduce coma for wide-field imaging. The Shelyak reducer uses an apochromatic triplet design optimized for on-axis color correction, which is more critical for preventing wavelength shifts and ensuring the scientific accuracy of your spectral data.
Will this 0.63x reducer work with my 8" Celestron SCT and an Alpy 600 spectroscope?
Yes, this is an ideal combination. The reducer will thread directly onto the 2-inch rear cell of your 8" SCT. The resulting f/6.3 focal ratio is perfectly matched to the input requirements of the Alpy 600, ensuring optimal illumination of its slit for low-resolution spectroscopy.
Does the Shelyak 0.63x reducer correct for coma or field curvature?
No, this is a dedicated focal reducer, not a corrector. Its primary design goal is focal reduction and high-fidelity color correction at the center of the field, where the spectrograph slit is placed. It is not designed to correct for off-axis aberrations like coma or field curvature, making it less suitable for wide-field deep-sky imaging than a dedicated reducer/corrector.
How do I attach the Shelyak 0.63x reducer to my telescope and spectrograph?
The reducer has female 2-inch SCT threads. You simply unthread your existing visual back or camera adapter from your telescope's rear cell and thread the reducer on in its place. The output side of the reducer has male threads that connect to other accessories, such as the Shelyak variable T-adapter (BA0027), which then connects to your spectrograph.
Can I use this reducer for deep-sky imaging of the Orion Nebula (M42) instead of spectroscopy?
While you can, it's not its intended purpose. The reducer will successfully shorten your exposure times by converting your scope to f/6.3. However, because it does not correct for coma, you will likely notice that stars away from the center of the field appear elongated or misshapen, an effect that would be noticeable across a large target like the Orion Nebula (M42).
