Australian Sky Telescope MayJune 2017

72 AUSTRALIAN SKY & TELESCOPE May | June 2017

WE ALL KNOWtheimportanceof

avoiding light pollution. But even if you

shield yourself from every light around

youthere’sstilloneenormoussource

of stray illumination: the sky full of

stars! Most of us don’t think of that as

aproblem,butifyou’retryingtotease

out the finer details of a distant galaxy,

everystrayphotonthat’snotpartof

your target becomes a contrast-reducing

part of the general background.

Fortunately Tom Osypowski, Howard

Banich,andChuckDethloffhavecome

up with the perfect solution.

Tomfirstsawtheideaatastarparty

backin1985.Someonehadgluedtwo

slabsofStyrofoamtothetopofhis

scope,makingatentthatshieldedthe

eyepiece from overhead light. Tom says,

“Myowntakewastomakeoneout

offoamboardthatVelcroedontothe

scope’s upper cage area. Then Howard

andChucktooktheoriginalideaand

perfected it.”

Perfection took some fiddling.

Howard remembers: “I came up with

amuchmorecomplicatedversion

madefromamixofmaterialsthat

could rotate around the focuser, which

worked but was rather flimsy and didn’t

The Dethloff eyepiece shade

How to block practically any light from your eyepiece.

rotateeasily.ThenChuckcameupwith

his salad bowl version, which solved all

theproblemsofmyversion,plusitwas

easytomake.MelBartelsdubbeditthe

Dethloff Eyepiece Shade.”

To make one, start with a lightweight

plasticsaladbowl.Ithastobebig

enough for your head, but small enough

to fit next to your finderscope. Chuck

says“Mostofthemwon’thavetall

enough sides. That’s okay though, as felt

wingscaneasilybeattachedtothesides

ofthebowltoprovideextraheight.”

Onceyou’vegotyoursaladbowl,

Chucksays,“You’llwanttocutouta

good part of the plastic bowl as a first

step,especiallythebottomhalf(asit

sits in your telescope’s focuser) almost

allthewaydowntothebaseofthe

bowl,soit’seasierforreachinginto

changeeyepiecesandalsotoallowa

pathformoistairtoescapewhenyou

exhale.Ialsoliketohaveagapatthe

topbetweenthetwofeltwings.This

allowsanotherpathforwarmmoistair

to escape.”

Aftershapingthebowl,cuta5-cm

holeinthebottom.Useaholesawwith

abackingboardanddrillslowly.

Afteryou’vemadethecutoutsand

gluedthefeltwingson,spray-paintthe

wholeworksflatblack,usingapaint

SChuck Dethloff's eyepiece shade also works

well for solar viewing and in humid conditions.

SMake a cutout in the side of the bowl that will face the ground, and add felt wings if necessary.

SNote that you can access the eyepiece

set screw through the gap in the shield. JUDY AND CHUCK DETHLOFF

that’s designed for plastic, and mount

it on your focuser. The shield is held in

place by the 2- to 1¼ ̋ adapter, or by a 2 ̋

eyepiece itself. You'll need to replace the

set screws with longer ones that extend

outward far enough to be accessible

behind the bowl. The shield can easily

be rotated as you raise or lower the

scope, so you can remain upright while

observing.

Both Chuck and Howard observe

with these light shields even under dark

skies. Tom reports, “I have used both of

their scopes with salad bowls attached,

and the effect is quite remarkable. All

you see is the field of view as presented

to you by the eyepiece. It’s a pleasure to

observe that way.”

ASTRONOMER’S WORKBENCH by Jerry Oltion