Daystar Quark Combo Gemini Chrom/Prom Switchable Solar Filter

An All-in-One 656nm H-Alpha Eyepiece Filter

The Quark Combo Gemini is an all-in-one Hydrogen-Alpha filter that inserts into a compatible telescope's 1.25" diagonal. It combines two complete, independently tuned Fabry-Perot etalon systems, a 25mm blocking filter, and precision heating electronics into a single, compact unit.

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.

0.5Å Chromosphere vs. 0.6Å Prominence Views

The Combo Gemini's core feature is its ability to present two fundamentally different views of the Sun. Push or pull the arm all the way until it stops to move one of the two hand-matched, SE-grade etalons into the light path, with no refocusing of any kind. Daystar qualifies one etalon to show best prominences and the other best surface contrast, and designates no specific FWHM.

• Chromosphere View (≤0.5Å): The narrower etalon, generally 0.5Å or below, appears darker but with more surface contrast. Filaments are only visible in the Chromosphere version; plage, active regions and spicules also show.
• Prominence View (≥0.6Å): The wider etalon, generally 0.6Å or above, appears brighter but with less surface contrast, since wider etalons pass more spectrum and appear brighter. The result is the broad stroked prominences of wider bandpass.

Optical Design: Engineered for F/15 to F/30 Telescopes

If light reaches the filter at an angle it causes wing shift. The manual rates the Combo Gemini for F/15 to F/30 refractors in full aperture, with best performance at F/27-F/32. Unlike the original Quark models, the Combo Gemini contains no internal barlow or focusing elements; it is a 0-power filter that relies on the host telescope's native or modified focal ratio.

For faster refractors, Daystar offers optional 2.8x and 4.3x telecentric barlows for the Combo Quark: the 4.3x for F/5 to F/9, showing the full disk at about 480mm focal length or shorter, and the 2.8x for F/5 to F/14, showing the full disk at about 720mm or shorter. You unscrew the snout and screw on the barlow.

Two SE-Grade Etalons with Instant Switching

At the heart of the Gemini are two separate, hand-matched SE-grade Fabry-Perot etalons. You push the slider arm side to side, like in an eye exam, with no equipment swapping or refocusing of any kind.

The Prom etalon appears brighter with less surface contrast and the Chrom etalon darker with more surface contrast, because wider etalons pass more spectrum.

Telescope Integration: Full-Disk Solar Views up to 1800mm

It passes the full solar disk for focal lengths under about 1800mm. The clear filter aperture is 21mm. There is no instrument aperture limit, allowing it to be used on large telescopes for high-magnification views of specific active regions.

• Refractors: Instruments with native focal ratios of F/15 to F/30 can use the Combo Gemini directly. Faster refractors require an optional Daystar 2.8x or 4.3x telecentric barlow to achieve the correct focal ratio.
• SCTs & Maksutovs: SCT and Mak users need an Energy Rejection Filter (ERF) specific to their telescope for safe operation. SCTs must use an off-axis ERF to reduce the aperture and slow the focal ratio. Maksutovs at a native ~F/15 do not need to reduce aperture but must use front mount energy rejection to prevent overheating of the optical tube assembly. The included 2° off-axis snout adapter is designed for use with these off-axis ERF setups.

Solar Safety: Energy Rejection

Concentrated sunlight can create very high temperatures where it falls, so care must be taken to prevent melted components or fire. To prevent damage, use an Energy Rejection Filter on telescopes of 80mm aperture or more, or when tracking the Sun for long periods: a UV/IR cut filter mounted before the diagonal, or a full aperture red or yellow glass ERF mounted in front of the telescope.

• For brief observing sessions with less than 80mm of aperture 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 Quark.
• For telescopes under approximately 120mm of aperture, a screw in UV/IR cut filter can be employed in front of the diagonal.
• For best performance, a red or yellow glass front mount ERF should be used; it is the safest option.
• All dedicated solar tracking applications should employ energy rejection.
• SCTs use an off-axis ERF with the wedge adapter; Maksutovs use front mount energy rejection.
• A Herschel wedge or white light filter cannot be used with the Quark: these pass very little light by design and give an extremely dark image.

Precision Tuning: ±0.5Å Wing Shift in 0.1Å Steps

Each etalon in the Combo Gemini has its own dedicated tuning knob, allowing you to precisely adjust the filter's center wavelength. Tune if the image lacks contrast; wing shift also shows Doppler-shifted features. The tuning range is ±0.5Å, adjustable in detented 0.1Å increments. The specification gives a settling time of approximately 10-20 minutes after power up or change of wing shift.

By turning the knob, you can shift the bandpass toward the blue or red wing of the H-alpha line. This allows you to enhance the visibility of solar features moving toward you (blue shift) or away from you (red shift). The independent knobs ensure your tuning settings for the chromosphere view are preserved when you switch to the prominence view.

5V, 1.5A USB Power for Field Operation

The Quark's etalons must be heated to a precise temperature to stay on the 656.28 nm H-alpha line. The Combo Gemini accomplishes this using a low-power heater that runs on a standard 5V USB connection. Any other USB power source must be rated for at least 2.0 amps at 5 volts; computer USB ports and cell phone chargers do not normally support this much power.

A 90-240VAC wall adapter with international plugs is included for home use. It can operate all day off a small, palm-sized optional battery pack (8-hour). An LED indicator shows the filter's status: yellow while warming up or tuning (a 10-20 minute process), green when it is on-band and ready for observation, and red to indicate a power fault like low voltage.

Visual Setup: 1.25" Snouts and Eyepiece Selection

The Combo Gemini is designed for simple visual integration. The sun-side features a standard 1.25" male snout with a safety indent that inserts directly into your telescope's diagonal. The eyepiece side has a 1.25" female drawtube with a brass compression ring to protect your eyepiece.

Because the filter operates at a slow focal ratio (F/15 to F/30), eyepiece choice is important. At F/30 a high powered eyepiece can exceed Dawes' limit, and best results come with an eyepiece of 32mm or greater. Plössl eyepieces of 32mm and 40mm are recommended, while Naglers, zooms, Radians and other fast eyepieces typically perform very badly.

Imaging at 656nm with CCD and DSLR Cameras

The Combo Gemini can also be used for imaging. For best results, use a monochrome CCD or CMOS camera, as on a color sensor only 1 in 4 pixels detect red light, giving 1/4 the sensitivity and 1/2 the resolution of a monochrome chip. Exposures should be very short, with frame rates under 1/10 second, because seeing cells move quickly.

To avoid interference patterns (Newton's rings) caused by the parallel surfaces of the filter and a camera sensor, tilt the camera 2 to 5 degrees as a starting point with the Daystar Interference Eliminator or Tilt Adapter accessories. Due to the long effective focal length, imagers with small sensors may require a focal reducer placed between the Quark and the camera to capture a wider field of view. Using a camera with a 12-bit or 16-bit ADC is also recommended to capture the wide dynamic range between bright plage and faint prominences in a single exposure.

Care, Storage, and the Daystar 5-Year Warranty

Proper care extends the life of your solar filter. When not in use, the Combo Gemini should be stored with its end caps on in the included hard case, preferably in a climate-controlled environment. Climate-controlled storage extends optical filter life expectancy up to 2-3 times. Dust may be blown off with a squeeze bulb, never compressed air, and the preferred cleaning method for fingerprints and smudges is factory cleaning.

Daystar provides a 5-year warranty covering defects in materials and workmanship. Blockers and trimmers are considered a wear item and are warranted on a pro-rated basis. The filter contains no user-serviceable parts, and opening the housing will void the warranty.