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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.
The 4.3X barlow will show full disk with approximately 480mm focal lengths or shorter. The filter performs better with a narrower bandpass with the 4.3X barlow, prioritizing surface contrast at the expense of a dimmer image as compared to the 2.8X barlow.
