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These brand new QUARK optimized accessories are designed to fit the classic Combo Quark Hydrogen Alpha Filter. Use a telecentric barlow by unscrewing the silver snout from the Combo Quark and screwing on the barlow.
The key to getting good performance out of an etalon based solar filter is to give it very parallel light, which can only be achieved with a true telecentric design. A good telecentric barlow will give a near constant magnification as the distance between the barlow and image plane is varied, which you can see as nearly flat lines in the chart below. Without the telecentric property you will encounter poor contrast and a central hot spot in the field of view.
For refractors from F/5 to F/14, the 2.8X barlow will show the full disk of the sun on refractors with a focal length of approximately 720mm or shorter. The 2.8X barlow will show a brighter, lower power image that is advantageous when using bino viewers that split the light between two eyes.
