Daystar Quark hydrogen-alpha eyepiece filters

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Daystar Quark hydrogen-alpha eyepiece filters

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We don't use the term 'game changer' lightly...

Interest in solar observing has developed at an amazing pace over recent years. A large reason for this is the introduction of affordable hydrogen-alpha solar filters, a category the Quark filters from Daystar certainly fit into.

Hydrogen-alpha filters give amazing views of the layer of hot hydrogen above the Sun’s visible white light surface, or photosphere. A hydrogen-alpha filter shows magnetically contorted hydrogen plasma mainly located in a layer known as the chromosphere.
Cooler ‘clouds’ of hydrogen can sometimes be seen above the chromosphere. Witnessed against the Sun’s disc, they appear as dark snaking filaments. As the Sun rotates, filaments are brought to the Sun’s edge where they appear to protrude into space as beautiful prominences.
To reveal all this majesty, a hydrogen-alpha solar filter needs to be manufactured to exacting tolerances. The filter must pass the hydrogen-alpha wavelength at 6,562.8 Ångströms (Å), with just a tiny wavelength range either side, known as the filter’s bandpass. This finesse is expensive to achieve but the introduction of the Coronado PST roughly a decade ago for around £500 changed the game. Even today though, moving to larger apertures tends to require deep pockets, and it is easy to stretch into five figures.

A surprise package

Enter the Daystar Quark. Unlike a typical hydrogen-alpha solar setup, the Quark does all the filtering at the eyepiece end and so, in theory, can be used with any size of aperture. As the Quark costs around £850, it’s quite an exciting prospect. 
The Quark is designed to work with refractors and it’s recommended that any instrument with an aperture over 3 inches should have an energy rejection filter (ERF) fitted over the front lens, at extra cost. Daystar provides an ERF configuration wizard online at 
This accessory is extremely simple to use. Insert it, power up and wait for the filter to get to operating temperature. A status LED turns green to show this has happened – for us, it took about 10 minutes.
Hydrogen-alpha filters are defined by their bandpass: wider bandpasses are suitable for prominences, while narrower ones show the finer details of the chromosphere. Daystar produces two Quarks; one for prominences (bandpass 0.8-0.6Å) and one for the chromosphere (0.5-0.3Å).
 The host refractor needs a focal ratio between f/4 and f/9. The Quark design incorporates an hydrogen-alpha optimised 4.3x telecentric Barlow, giving a magnification 4.3x higher than prime focus. So an f/9 telescope would operate effectively at f/38.7.
If you think that an £850 hydrogen-alpha eyepiece advertised as “Quick, cheap, easy and fun” produces a compromised view, then you’d be wrong. The views through both versions of the Quark eyepiece were superb. As you’d expect, larger apertures delivered the most impressive results.
The Quark Chromosphere delivered sharp, fine detail with excellent contrast, while the dramatic rendition of hydrogen-alpha detail around active regions was breathtaking. The filter’s temperature can be adjusted slightly, which causes the Quark to go off-band. This is used to study material moving at high speed towards or away from you, which may be slightly blue- or redshifted. It’s necessary to give the filter about 10 minutes to reach optimum temperature after each retune. Where the chromosphere is seen at the Sun’s limb, short-lived columns of plasma measuring 500km across and thousands of kilometres high can be seen. Called spicules, both Quarks revealed these with ease during our tests.
The Quark Chromosphere shows prominences, but isn’t optimised for them. That's the job of the Quark Prominence, which also shows the chromosphere. We were impressed at the difference between views of the same feature when swapping versions. If you were thinking of getting just one Quark, we’d recommend the chromosphere version simply because of the variety of features it can reveal.
A camera can be used with both Quarks. Our recommendation would be to use a high frame rate monochrome one; during our tests, we achieved some excellent imaging results with the filters.
Daystar has been producing eyepiece-based solar filters for years, but this is its first budget model. The good news is that it appears they’ve got the product developed right and as it stands the Quark has the potential to be something of a game changer. The ability to experiment with different apertures and configurations all for £850 is very attractive indeed.
Optimised to perfection
The small wait for each filter to get to temperature fills you with anticipation and your eventual opportunity to look through the eyepiece or via a camera certainly doesn’t disappoint. Despite the diminutive (in hydrogen-alpha terms) price tag, both models perform impressively.
The chromosphere-optimised version shows plenty of fine detail, from dark fibrils, filaments and plage to intricate magnetic maelstroms surrounding active regions. Despite its optimisation, this version can also show limb detail including prominences and the short-lived jets of gas known as spicules. The field of view has great contrast and is without gradients or noticeable sweet spots.
Switching from the chromosphere to the prominence model delivers a whole new experience. Seeing prominences via the chromosphere filter leads you into the false sense that the prominence filter view isn’t going to be that much better. However, it is. Prominences appear bright and detailed against a jet black background sky again with no sweet spot issues.

Hydrogen-alpha filter - All the optics are fully encased in a solid body. This contains an integrated and fully baffled, two-element telecentric 4.3x Barlow optimised for the hydrogen-alpha wavelength. The filter has a clear 21mm aperture and is fitted with a 12mm blocking filter. It’s possible to view the whole of the Sun’s disc through a telescope with a focal length of 450mm or less.

Status LED - A status LED provides basic filter information. When initially powered up the light is an orange colour, but this changes to green when the filter temperature reaches the point where it’s centred on the target wavelength. 
Power - The Quark requires a 5V, 1.5A power feed for operation. The input port for this uses a micro USB plug (Micro B). A mains adaptor with plug fittings for different countries is supplied as standard, including one for the UK. An optional eight-hour battery pack is also available, should you want to make the Quark portable.
Tuning knob - A small knob retunes the filter to operate in the narrow wings either side of the central hydrogen-alpha wavelength of 6,562.8Å. The knob clicks in increments of 0.1Å, providing maximum variation from the central wavelength by +/–0.5Å. Retuning allows you to follow fast-moving material that is heading away or towards you and so appears slightly redshifted or blueshifted as a consequence.
2- OR 1.25-inch output barrel - Quark eyepieces fit between your telescope and your regular eyepiece or camera. The telescope end can fit into a 2- or 1.25-inch eyepiece barrel. At the other end, a 1.25-inch compression ring barrel is provided. Optional 2-inch and Schmidt-Cassegrain fittings are also available. The compression ring grips securely when the thumbscrew is tightened and prevents damage to whatever’s been inserted.

This review originally appeared in the October 2014 issue of BBC Sky at Night Magazine. All prices correct at time of going to press.


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