What is the purpose of the Shelyak 50µm object fiber in an eShel system?
This is the "object" fiber, designed to carry the starlight collected by the telescope to the spectroscope. It physically connects the Fiber Injection and Guiding Unit (FIGU) at the telescope to the main eShel instrument, which can be located up to 20 meters away.
Why is the attenuation of the 20m fiber rated at <0.5dB, the same as shorter fibers?
For modern optical fibers of this length, signal loss along the glass itself is negligible (close to 100% transmission). The vast majority of the <0.5dB attenuation occurs at the two FC connector junctions. Because the number of connections is the same regardless of length, the total attenuation remains constant across 5m, 10m, and 20m versions.
Can I use this 50µm object fiber to study the Balmer series in Vega (Alpha Lyrae) with an eShel?
Absolutely. The fiber's High-OH glass provides excellent transmission from 380nm to 800nm. This range comfortably covers the entire visible Balmer series of hydrogen, from H-alpha (656nm) down to H-beta (486nm), H-gamma (434nm), and H-delta (410nm), making it ideal for stellar classification of A-type stars like Vega.
What does "High-OH" mean for this 50µm fiber?
"High-OH" refers to a high concentration of hydroxyl groups in the silica glass, which significantly improves the fiber's transparency to blue and ultraviolet (UV) light. This makes the fiber highly efficient for spectroscopy in the 380nm to 800nm range, ensuring faint signals in the blue end of the spectrum are not lost.
I have my telescope and eShel spectroscope set up 15 meters apart. Is the 20m fiber the right choice?
Yes, the 20-meter length is the correct choice. It provides the necessary distance with extra slack to prevent strain on the fiber or connectors as the telescope moves. Since attenuation is independent of length in this range, there is no performance penalty for choosing the 20m version over a shorter one.
What kind of connectors does the Shelyak 50µm object fiber use?
The fiber is terminated with FC-type connectors on both ends. This is a standard, robust connector used in spectroscopy and telecommunications to ensure precise and repeatable alignment of the fiber core.
