When The ED81S was introduced , it set a new standard for APO Refractors. The combination of better color correction from the new ED glass and brighter images from its fast f/7.7 focal ratio will satisfy the most demanding visual astronomer or astro-photographer. The new ED glass produces clear and high contrast viewing, virtually free of false color. Vixen's innovative design uses newly developed, environmentally friendly glass technology. The optical tube is very stable yet light weight. The top carry handle also includes a 1/4-20 stud for piggyback camera mounting. Vixen's new Dual Speed Focus, now standard on the ED81, provides fine focus adjustments for 1/7th speed focusing.