The William Optics Guidestar 61 APO (Apochromatic) telescope is a 61mm refractor telescope that is optimized for deep-sky and planetary observations. It features a doublet objective lens made of FPL-53 ED glass, which provides excellent color correction and sharp images. The telescope’s compact design and portability make it a popular choice for amateur astronomers. Additionally, the Guidestar 61 APO has a dual-speed 10:1 focuser for precise focusing and a built-in electronic focusing system for easier guiding during long exposure astrophotography.
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.
- Focal Length: 360mm
- Diameter: 61mm
- Focal Ratio: F5.9
- Tube Length: 340mm
- Tube Weight: 1.44kg