| The Takahashi #VARI variable extender (vari-extender) consists of a 1.6x tele-negative amplifier (Barlow) with three 40mm long extension tubes that thread onto the focuser drawtube of Takahashi refractors. It increases their focal length by 1.6x to 3x for photography and visual observing. Up to four additional #VARI-T extension tubes be stacked onto the #VARI’s standard equipment tubes for greater focal length gain (up to 4.8x). The #VARI adapter becomes quite long and unwieldy with all these tubes attached, however. Many observers prefer to increase their magnification by adding this optional 2x doubler lens to the vari-extender, instead of stacking extension tubes. Using this doubler in combination with the 1.6x lens and the standard extension tubes results in a 3.2x to 6x photographic gain, depending on the number of extension tubes used. The doubler can also be used visually, doubling the magnifications that the #VARI provides. However, due to back focus considerations, the doubler can not be used visually with a star diagonal. This makes it inconvenient for celestial observing near the zenith. This fully-multicoated doubler threads onto the telescope focuser drawtube after the scope’s eyepiece holder is removed from the focuser. The #VARI extender is in turn threaded onto the doubler and its extension tubes stacked onto the #VARI’s 1.6x lens as normally. The doubler has a rubber grip ring to make it easier to assemble and disassemble in cold weather when wearing gloves. For maximum image contrast, the interior of the doubler is painted matte black, in addition to being antireflection threaded.
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