Daystar Sodium D-Line Quark eyepiece filter.
This little-used wavelength is a welcome addition for solar astronomers
Using the sodium wavelength of light for solar astronomy is not a new concept, but one traditionally considered as being quite exotic by amateur astronomers. Perhaps it will become a bit more accessible now that Daystar has added a sodium D-line eyepiece filter to its Quark range.
This eyepiece filter has a bright gold housing at the top to distinguish it from the other Quark variants, but its shape is the same as the original hydrogen-alpha model on account of the 4.3x telecentric Barlow lens housed within. On top of the unit is a 1.25-inch eyepiece holder, on the bottom 1.25-inch and 2-inch mountings for a telescope. As with all of the other Quarks, it has a wing shift control knob and a power supply is included.
The eyepiece filter is designed for air-spaced refractors that have focal ratios of f/4-f/9, and can be used in conjunction with an ultraviolet/ infrared-blocking filter. If you need to use an energy rejection filter (ERF), make sure it is a yellow one – a red ERF won’t allow the sodium D-line through.
This is quite an exciting product for solar astronomers in the UK as it has a 589nm bandpass, a good area of the spectrum with respect to poor weather conditions or a low winter Sun. Here we are looking at the Sun’s photosphere, and in some ways the view through the D-Line can look similar to that given by a white light filter. The changeable UK weather conditions can cause all sorts of issues with solar astronomy – calcium, hydrogen-alpha and white light can produce quite poor results in mid-winter. By narrowing the wavelength, the unwanted parts of the light spectrum are removed and this then gives us a cleaner view of our star.
Setup is easy: all you need to do is attach the ultraviolet/infrared-blocking filter to the front of a star diagonal and then insert the eyepiece filter itself.
Quiet success
The Sun has started to enter a quiet period but we were fortunate to witness a reasonably sized sunspot for our first test, using the Quark in conjunction with a 25mm eyepiece and a 6-inch, f/6 Altair Starwave refractor. The Sun appeared a nice yellow colour, the detail in and around the sunspot sharp and crisp. However, the view was quite bright and this did lead to