Products

Accessories: Crayford Focuser

The Burgess Optical Crayford Focuser is a low-cost replacement for rack and pinion focusers. The Crayford Focuser has an assortment of adapter plates for mating the Focuser to various sized refractors and reflectors.

The Focuser has a 2" focuser tube and comes with a 1-1/4" accessory adaptor. Both the 2" tube and the 1-1/4" adapter have compression rings.

On the bottom of the Crayford Focuser is a tension adjustment (the upper knob in the picture) and a focuser tube lock (the lower knob). The tension adjustment should be tightened if the focuser tube slides out when using the focuser. Normally, the tension adjustement knob is set tight. The focuser tube lock prevents the focuser tube from moving, and the focus knobs freewheel.

The focuser tube is fully threaded and the threads are painted flat black to prevent unwanted reflections. The focuser tube moves against ball bearings inside the focuser. Over time, the focuser tube will become burnished where the ball bearing bear against the tube. This burnishing will not affect the focuser performance.

The Crayford Focuser does not include a fine-focus adjustment. Neither does the Focuser include a finder base, although, there is provision for adding a Synta/Orion style dovetail finder base to the focuser body. If desired, one user has reported success in collimating the focuser. Click here to see the procedure for adjusting collimation.

When replacing a focuser on an existing telescope, the distance from the end of the scope tube to the end of the focuser tube needs to be considered. The Focuser with the 80mm refractor base is shorter than the stock 1-1/4" focuser on most short tube 80 scopes, however, a 2" diagonal has a longer optical path (about 1-3/4" longer) than a 1-1/4" diagonal. But, with a 1-1/4" diagonal, there should be no problems reaching focus when making a direct replacement of the focuser.

Specifications

* Dimensions are plus-or-minus 1/16", 1mm.

Available accessories include a wide assortment of telescope adapter bases sized to fit many telescopes. The refractor bases attach to the telescope tube with three screws spaced around the circumference of the adapter base. The screw-holes in the adapter bases are threaded. The reflector bases are curved plates with for holes for attaching the plate to the reflector tube.

Also available is a finder base that screws onto the top of the Focuser. The finder base accepts Synta/Orion style dovetail finder mounts.

Alternatively, an MRF^TM finder can be installed on the telescope tube using the included base or the optional Synta/Orion type base.

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