Daystar Quark Gemini Chrom/Prom Switchable Solar Filter

An All-in-One, Dual-Bandpass 6562.8 Å Solar Filter

The Quark Gemini is an all-in-one H-alpha filter for refractors. It contains two distinct etalons, a 12mm blocking filter, and a 4.3x telecentric barlow. This all-in-one design eliminates the complexity of stacking separate components.

Outreach astronomers can use the prom vs chrom switch to demonstrate each feature, with an extra teaching moment about wing shift in fast moving prominences, and imagers can use it to create comparison images without exchanging equipment or refocusing on short lived features. Rather than choosing between the Chromosphere and Prominence models, the Gemini gives you both.

Chromosphere vs. Prominence Views at ≤0.5Å and ≥0.6Å

The Gemini's two etalons are selected to provide two fundamentally different views of the Sun. With a push of the slider, you engage the Chromosphere etalon, which has a bandpass of 0.5Å or less. This narrower window gives more surface contrast; filaments are only visible in the Chromosphere version.

• Chromosphere View (≤0.5Å): Dark, thread-like filaments stand out against the brighter surface. Active regions, bright plage around sunspots and spicules at the limb are also shown.
• Prominence View (≥0.6Å): Sliding to the other position engages the ≥0.6Å etalon. This wider bandpass gives broad stroked prominences in a brighter image.

The Integrated 4.3x Telecentric Barlow System

A Fabry-Perot etalon's performance is critically dependent on the angle of light passing through it; it requires a slow, near-parallel beam (F/15 to F/30) to achieve its specified bandpass. The Quark Gemini's integrated 2-element, 4.3x telecentric barlow achieves this for F/4 to F/9 refractors.

This custom optical system is fully baffled and optimized specifically for the 656nm H-alpha wavelength, and it offers superior field flatness. For a telescope operating at F/7, the barlow gives about F/30. This built-in solution means you don't need to calculate or purchase a separate barlow, as the optical correction is already part of the design.

Two SE-Grade Etalons and Instant, Parfocal Switching

At the heart of the Gemini are two hand-matched, SE-grade Fabry-Perot etalons. A simple, robust slide mechanism moves one etalon or the other into the light path. You can push the slider arm side to side, like in an eye exam, with no equipment swapping or refocusing of any kind.

Compared with two separate Quark filters, the Gemini keeps both etalons in one device with one power cable, so there is no filter to swap and no refocusing. This is ideal for outreach, where you can demonstrate the difference between surface and limb detail, and for imaging, where you can capture both without losing time on a short-lived event.

Optimized for F/4 to F/9 Refractors

The Daystar Quark Gemini is specifically designed for use with refractor telescopes with focal ratios from F/4 to F/9, with best performance between F/4 and F/8. With the integrated 4.3x barlow these give an F/17 to F/38 final image. The filter is not suited for off-axis (SCT or dob) application. Daystar's store page gives F/5 to F/8 refractors; its manual gives F/4 to F/9.

The 4.3x magnification factor means the Gemini is best suited for high-magnification views of specific regions. On refractors with a focal length under about 450mm, you can still frame the full solar disk. On longer instruments, you will be exploring sections of the Sun, for detailed studies of active regions, sunspot groups, and large prominence structures.

Solar Safety: Energy Rejection for Apertures Over 80mm

The Quark Gemini contains an integrated 12mm blocking filter, with off-band blocking from X-ray to 2 microns. Concentrated sunlight can create very high temperatures where it falls, so care must be taken to prevent melted components or fire, and an Energy Rejection Filter is recommended on telescopes of 80mm aperture or more, or when tracking the Sun for long periods.

• Less than 80mm of aperture: For brief observing sessions when not using a tracking mount, it can be OK to use no energy rejection at all. Be alert for any rise in temperature of your telescope, diagonal or filter.
• 80mm of aperture or more: Use energy rejection: for telescopes under approximately 120mm, a screw-in UV/IR cut filter in front of the diagonal reflects UV and IR light back out the front of the telescope; for best performance, a red or yellow glass front mount ERF should be used.
• Dedicated Tracking: All dedicated solar tracking applications should employ energy rejection.

A Herschel wedge or white light filter cannot be used with the Quark: these pass very little light by design and would give an extremely dark image.

Precision Tuning: ±0.5Å Wing Shift and 10-20 Minute Warm-Up

Each of the Gemini's etalons has its own dedicated tuning knob, allowing you to fine-tune the filter's central wavelength. The knobs provide a wing shift of ±0.5Å from the central 6562.8 Å line, with distinct detents every 0.1Å. This lets you restore contrast if the view lacks it and observe Doppler-shifted features.

A feature moving towards you will be brighter in blue (counter-clockwise) wing shift, and one moving away will be reddened (clockwise). After plugging in the filter or adjusting the tuning, the unit requires approximately 10-20 minutes for the internal heater to stabilize the etalon's temperature. The LED indicator turns from yellow (settling) to green when it is on-band and ready for observation.

5V, 2.0A USB Power for Precision Heating

The Quark Gemini's ability to stay precisely on the H-alpha bandpass depends on its internal heating system, which maintains the Fabry-Perot etalons at a constant, elevated temperature (approximately 100-150°F). This system requires a stable USB power source capable of delivering 5V at 2.0A (10W).

The filter includes a 90-240VAC wall adapter with a set of international plugs (US, UK, Euro, Australian) for use at home. For field use, you can power it with an optional 8-hour battery pack or any other USB power source rated for at least 2.0 amps at 5 volts. Computer USB ports and cell phone chargers do not normally support this much power.

Visual Ergonomics: 1.25" & 2" Snouts and Eyepiece Selection

The Gemini is designed for straightforward integration into your existing setup. It features a versatile combo male snout that fits directly into both 1.25" and 2" diagonals or focusers, secured by a safety indent. The eyepiece side has a standard 1.25" female drawtube with a brass compression ring to protect your eyepiece.

Due to the long effective focal length created by the 4.3x barlow, eyepiece choice is important. Plössl eyepieces of 25mm, 32mm and 40mm are recommended; at long focal ratios a high-powered eyepiece can exceed Dawes' limit, so an eyepiece of 32mm or greater gives the best results.

Solar Imaging with the Quark Gemini

For imagers, the Gemini allows capture of both high-contrast surface detail and bright prominences in a single session. For best results, use a monochrome camera, as a color sensor's Bayer matrix only uses one in four pixels for red light, reducing both sensitivity and resolution at the H-alpha wavelength.

To connect a camera, optional T-thread and C-mount adapters are available. A common issue when imaging in monochromatic light is the appearance of interference patterns (Newton's Rings). This can be corrected by using an optional tilt adapter to slightly angle the camera sensor relative to the filter. Because the Quark produces a large image scale, imagers with smaller sensors may also benefit from an optional focal reducer to capture a wider field of view.

Pelican Case Storage and 5-Year Warranty

The Quark Gemini is a precision optical instrument that requires proper care. It ships in a watertight pelican style equipment case for dust and humidity-free storage. Climate-controlled storage extends optical filter life expectancy up to 2-3 times.

Daystar backs the Quark Gemini with a 5-year warranty, covering defects in materials and workmanship. Daystar considers blockers and trimmers wear items and are covered on a pro-rated basis over the five-year term.