"This eyepiece could reach the focus only if the focuser was just one or two millimeters shorter"..... Maybe most telescope users have had similar experiences as such. To solve this irritating problem, Kasai produced a simple and resonable solution: "Focal Point eXtracting (FPX)" Filters. Broadband multi-coated 3mm thickness non-color "optical flat" is mounted in a filter cell. Just attached to the filter threads of your eyepiece, diagonal, camera adapter or other accessory, the focal point can be 1mm "extracted" automatically. Utilizing high-quality flat optical glass, no image deterioration or aberrations or color changes are detective. Of course the magnification stays the same. It's also possible to stack two or three FPX Filters to add the focus extracting range by 2mm or 3mm increasingly. With this unique aid, get all your eyepieces to reach the focus with all your observing instruments.
<Recommendable Situiations to use Kasai FPX Filters> *A particular eyepiece can't slightly reach the focus with a particular telescope. *Particular eyepeice pair can't slightly reach the focus with a binocular telescope. *Prime-focus photo adapter can't slightly reach the focus with a Newtonian telescope. *Binocular viewer can't slightly reach the focus with a particular telescope. *Some eyepieces can't slightly reach the focus because of strongly shortsighted eyes. .... etc. Try Kasai FPX Filter whenever you feel "if only just a little more backfocus......"

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