Wil­liam Op­tics GT71 apo re­frac­tor

Sky at Night Magazine - - CONTENTS -

The GT71’s apochro­matic triplet lens is man­u­fac­tured from high qual­ity op­ti­cal glass, in­clud­ing FPL-53 el­e­ments with high trans­mis­sion coat­ings, all held in place with a CNC-ma­chined ad­justable cell. By us­ing three lenses in this way, the dom­i­nant colours of the spec­trum can be brought to­gether in close fo­cus. As­tropho­tog­ra­phers will be able to en­joy pin­point star im­ages with­out bloated colour haloes, while vis­ual ob­servers will get to ap­pre­ci­ate the views of bright tar­gets such as the Moon or plan­ets free from dis­tract­ing colour fringes and colour aber­ra­tions.

The fo­cal length of the tele­scope is 420mm, giv­ing a sen­si­ble fo­cal ra­tio of f/5.9. This in turn en­ables as­tropho­tog­ra­phers to speed­ily cap­ture pho­tographs of large neb­u­lae and ex­tended deep-sky ob­jects. In­deed, all our cap­tured im­ages were short un­guided ex­po­sures. The ex­cel­lent colour-cor­rect­ing prop­er­ties of the tele­scope make it em­i­nently suit­able for DSLR and one-shot colour CCD pho­tog­ra­phy, ap­peal­ing to those de­sir­ing a sim­ple and com­pact op­tion for hol­i­day or travel as­tron­omy.

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