William Optics GuideStar 61 Guide Scope and APO Doublet Refractor (Soft Carry Case Included) - OPENBOX

Use as a portable high quality imaging scope or an ultra-high quality guidescope.

The new William Optics GuideStar 61 APO features the same high quality FPL53 ED doublet lens as the Zenithstar 61 so delivers sharp, high contrast images virtually free of false-colour. 

Other features include a new lightweight optical tube with draw-tube (push-pull) focuser for coarse focusing and a rotating lens assembly for fine focus. 

Two flatteners are available for the GuideStar 61: the existing Adjustable Flattener for the ZS61 and a new 0.8x Reducer/Flattener. 

CNC machined aluminium for a superior fit and finish. 

Supplied with a Vixen/Synta style finder dovetail rail (for a finder-scope) and a soft carry case. 

Ohara FPL-53 vs FPL-51 ED Glass

The dispersion properties of ED and SD glass elements are important in determining the overall colour correction. The abbe index is used to quantify the 'partial dispersion' of a particular glass. Pure Fluorite offers the highest partial dispersion at around 94.99 V, Ohara FPL-53 glass is very close to Fluorite at 94.93 V and is often referred to as Synthetic Fluorite.  FPL-53 is also noticeably better than Ohara's lower spec' FPL-51 glass which offers an abbe index of 81.54 V.

Specification

• Focal Length: 360mm
• Diameter: 61mm
• Focal Ratio: F5.9
• Tube Length: 340mm
• Tube Weight: 1.44kg