| This is an excellent quality 1.25" fully multicoated 2x achromatic doublet Barlow. It is designed to provide 2x magnification when used in front of a 1.25" star diagonal (with the diagonal inserted into the Barlow), rather than being inserted into the star diagonal’s eyepiece tube (with the eyepiece then being inserted into the Barlow).
However, the Barlow’s short 3.5" length does allow it to be used in star diagonals, although its magnification will be less than the specified 2x when used in a diagonal, rather than in front of the diagonal as designed. When used in a star diagonal, the Takahashi Barlow typically will not seat fully down into the eyepiece holder of the diagonal. Generally, 1/4" (to a worst case 1/2") of the Barlow's chrome barrel will remain exposed when the Barlow is fully seated against the stop at the base of the diagonal’s eyepiece tube. This does not affect the Barlow’s safety, as the full width of the diagonal’s clamp ring (or the diagonal’s thumbscrew) will be fully engaged with the chrome barrel of the Barlow. There is no danger of the Barlow coming loose if the diagonal’s clamp ring or thumbscrew is properly tightened.
A non-marring molded compression ring in the Barlow automatically centers your diagonal in the light path for sharpest images as it holds your diagonal in place without scratching its chrome barrel the way the ordinary metal thumbscrew-type holders on lesser Barlows often do. A simple twist of the knurled compression ring collar lets you apply as much or as little pressure on the soft compression ring as you prefer to hold the diagonal in place, without the danger of scratching the diagonal barrel. Also, no thumbscrew means no danger of losing the thumbscrew in the field.
The Barlow has blackened internal antireflection threading for improved contrast and will not affect the color correction of Takahashi apochromatic fluorite refractors.
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