The Testar 50mm Guide Scope has a focal length of 190mm and a focal ratio of f/3.8. The objective is a fully multi-coated achromatic doublet for a greater optical precision. The border of the lenses are blackened to deliver a higher contrast. The 69mm support rings have 3 screws with a nylon tip for a perfect alignment with the main telescope. Having the guide scope aligned to the main telescope increases the guiding accuracy and it reduces the field rotation displayed in the capturing camera. The mini dovetail bar can be firmly mounted on any standard finder scope bracket so you do not require any extra piggy back dovetail bar on top of your telescope. The 31.8mm / 1.25" non-rotary helical focuser permits a micrometric focusing adjustment while a quick release draw tube offers an initial coarse focusing. Designed to use with many guiding cameras it can be used as a great optical finder by adding a 31.8mm diameter eyepiece. This 50mm compact guide scope has an accurate helical focuser that keeps the orientation of the connected camera.Note that with rotative focusers the cables of the guide camera could get twisted while focusing. The precision helical focuser has a 10mm travel while the fast focus device has a 30mm excursion. Testar 50mm Guide Scope with QHY 5L-II camera - focus ring extension approx. 30 mm. Testar 50mm Guide Scope with ZWO ASI120MM-S camera - focus ring extension approx. 13 mm. Testar 50mm Guide Scope with ZWO ASI120MM Mini camera - focus ring extension approx. 30 mm. Specifications Objective lens diameter 50 mm Focal length 190 mm Camera/eyepiece connection 1.25" and male M42 Weight 588 gr Max tube length 245 mm (focuser fully extended) Focus travel 0~40 mm Focuser type Non-rotative micrometric with locking screw Dovetail Specifications 30.8 mm x 89 mm - fits finder scope brackets Dovetail threads 1 x 1/4" , 2 x M8 female thread Included items Guide scope 50mm Tube rings Objective lens cap Eyepiece cap Mini dovetail bar for finder scope brackets x 6 nylon tipped screws x 2 bolts for dovetail-tube rings connection Allen key
