How To...

Build a right-an­gled po­larscope adap­tor.

Sky at Night Magazine - - CONTENTS - STEPHEN TONKIN is au­thor of Binoc­u­lar Astron­omy and edi­tor of binoc­u­larsky.com

The sim­ple DIY so­lu­tion to tak­ing the back strain out of the align­ing process

Do you en­joy get­ting damp knees, back-ache and a stiff neck as you strug­gle to use the eye­piece of your po­larscope when you’re try­ing to get your mount de­cently aligned? No? Nei­ther do we.

There’s not much point in an equa­to­rial mount un­less it’s prop­erly aligned but, mar­vel­lous as po­lar align­ment scopes are, they have never been de­signed for com­fort. Be­ing un­com­fort­able isn’t just un­pleas­ant, it’s also a dis­in­cen­tive, so you have to wel­come any way of mak­ing the po­lar align­ment process less of a back strain.

There are sev­eral soft­ware so­lu­tions, and you can even fit a cheap we­b­cam to the po­larscope so that you can view the align­ment retic­ule on a screen. But these all add com­plex­ity to what, in a per­fect world, should be a quick and sim­ple process. The ideal so­lu­tion for fre­quent po­lar align­ment, es­pe­cially when you’re us­ing a portable track­ing mount in the field, needs to be one that doesn’t re­quire com­put­ers, elec­tri­cal power or the skills of a con­tor­tion­ist.

The dis­com­fort arises from two fac­tors. Firstly, the po­larscope, from UK lat­i­tudes, must be aimed at an el­e­va­tion of 51° or higher. Your neck has not evolved to the point where you can com­fort­ably look up at that an­gle ex­cept for short pe­ri­ods. Se­condly, the po­larscope eye­piece may be at chest height or lower. For­get about sit­ting: putting a seat in the re­quired po­si­tion re­sults in a ter­ri­to­rial dis­pute be­tween the chair’s legs, the tri­pod’s legs and your legs. Get­ting your eye in the right po­si­tion re­quires ei­ther kneel­ing or bend­ing your back at the sort of un­nat­u­ral an­gle that con­tra­venes ev­ery chi­ro­prac­tor’s idea of good pos­ture. Both bend­ing and

kneel­ing in­crease the temp­ta­tion to use the tri­pod as a sup­port when you get to your feet, af­ford­ing you ev­ery op­por­tu­nity to knock the sys­tem out of align­ment again. Plus, kneel­ing leads to wet knees.

The sim­plest so­lu­tion is the one that we all use at the eye­piece of a re­fract­ing tele­scope: a star di­ag­o­nal. For­tu­nately, the es­sen­tial com­po­nents are read­ily avail­able at rea­son­able cost. The heart of this project is a right-an­gled fin­der at­tach­ment de­signed for use with the viewfinder of a DSLR cam­era.

There are sev­eral dif­fer­ent types avail­able and your choice should be dic­tated by the ease with which it can be fixed to the tube that will go over the po­larscope’s eye­piece. The Pen­ta­con­branded one is par­tic­u­larly suit­able be­cause it has a bay­o­net-type con­nec­tor that merely re­quires you to cut a shaped aper­ture in the con­nect­ing tube and not have to bother about drilling screw-holes or mak­ing com­pli­cated mat­ing pieces.

Find­ing a cheap fin­der

Many sec­ond-hand find­ers have lost the at­tach­ment that slips over the cam­era’s viewfinder sur­round, and so are avail­able very cheaply. A right-an­gled fin­der also gives a cor­rect im­age, so you don’t have to al­low for a re­versed po­larscope retic­ule. If your po­larscope has a 30mm di­am­e­ter eye­piece, such as the com­mon Sky-Watcher or Vixen ones, the tube can be fash­ioned from ei­ther a 35mm film can or a 36mm ABS waste-pipe stop. Al­ter­na­tively, it could be a use­ful 3D-print­ing project.

You need to use loop tape to make the tube fit snugly to the eye­piece. Trial-andim­prove­ment is the best method for de­ter­min­ing the ap­pro­pri­ate amount to use. It needs to be enough to pre­vent the fin­der from fall­ing off, ro­tat­ing or tilt­ing, but not so much as to make it dif­fi­cult to get it on or off.

To use your new cre­ation, first roughly align your mount. A bright pen­light torch shone up the po­larscope eye­piece, pro­duc­ing a col­li­mated beam that you can di­rect at Po­laris, is use­ful for this (as long as do­ing so won’t in­con­ve­nience fel­low ob­servers). If nec­es­sary, set the po­larscope’s time and date, put the fin­der on the po­larscope and place Po­laris in the ap­pro­pri­ate part of the retic­ule. Then take it off and en­joy a com­fort­able ob­serv­ing or imag­ing ses­sion with dry knees and an ache-free back and neck.

Align­ing your po­larscope in a com­fort­able stand­ing po­si­tion is not just a dream

With Stephen Tonkin

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