DIY:DIY:

field of viewfield of view

templatestemplates

Blake NancarrowBlake Nancarrow

why?why?

�� sense of scalesense of scale

�� eyepiece selectioneyepiece selection

�� star hoppingstar hopping

inspirationinspiration

�� wire rings wire rings

Sky & TelescopeSky & Telescope

�� acetate template acetate template

with with TirionTirion

what you needwhat you need

�� telescope & eyepiece datatelescope & eyepiece data

�� star chartstar chart

�� rulerruler

�� calculator or spreadsheetcalculator or spreadsheet

�� drawing or presentation softwaredrawing or presentation software

�� printer (ideally laser)printer (ideally laser)

�� acetate film or transparency sheetsacetate film or transparency sheets

processprocess

1.1. gather telescope data (finder too)gather telescope data (finder too)

2.2. gather eyepiece data (gather eyepiece data (binosbinos too)too)

3.3. calculate TFOV sizescalculate TFOV sizes

4.4. get scale of star chartget scale of star chart

5.5. draw scaled TFOV ringsdraw scaled TFOV rings

6.6. test printtest print

7.7. final printfinal print

telescope datatelescope data

�� focal lengthfocal length

telescope data telescope data –– exampleexample

�� focal length (in mm)focal length (in mm)

–– CelestronCelestron SPSP--C8: 2000C8: 2000

–– Edmund SSC 6": 1220Edmund SSC 6": 1220

eyepiece dataeyepiece data

�� focal lengthfocal length

�� apparent field of view (AFOV)apparent field of view (AFOV)

–– manufacturer literaturemanufacturer literature

–– fine folks on internetfine folks on internet

–– drift testsdrift tests

eyepiece data eyepiece data –– exampleexample

72723636baaderbaader

hyperionhyperion--asphericaspheric

40401818MeadeMeade

orthoscopicorthoscopic

52522626CelestronCelestron

plplöösslssl

AFOV (AFOV (°°))fl (mm)fl (mm)

calculatecalculate

�� TFOV = TFOV = AFOVAFOVepep / ( / ( flfltt / / flflepep ))

�� where:where:

–– TFOV = true (real) field of viewTFOV = true (real) field of view

–– AFOVAFOVepep = apparent field of view eyepiece= apparent field of view eyepiece

–– flfltt = focal length telescope= focal length telescope

–– flflepep = focal length eyepiece= focal length eyepiece

calculate calculate –– exampleexample

eyepiece flep AFOVep flt TFOV (°)

baader 36 72 2000 1.296

Celeston 26 52 2000 0.676

Meade 18 40 2000 0.360

baader 36 72 1220 2.125

Celeston 26 52 1220 1.108

Meade 18 40 1220 0.590

binos 376' at 1000 yards 7.162

chart scalechart scale

�� measure with accurate rulermeasure with accurate ruler

�� watchoutwatchout

–– scales may varyscales may vary

chart scale chart scale –– exampleexample

�� Pocket Sky AtlasPocket Sky Atlas

18.3 cm = 3518.3 cm = 35°°

7.15 cm = 157.15 cm = 15°°

�� average ratio ofaverage ratio of

°° per cm:per cm:

0.49910.4991

make ringsmake rings

�� use a presentation appuse a presentation app

–– PowerPoint (Window$)PowerPoint (Window$)

–– Impress (Linux)Impress (Linux)

–– Keynote (Mac)Keynote (Mac)

�� use a drawing appuse a drawing app

–– Illustrator or FireworksIllustrator or Fireworks

–– (OO) Draw(OO) Draw

�� calculate scaled ring sizescalculate scaled ring sizes

make rings make rings –– exampleexample

eyepiece scope TFOV (°) ring (cm)

baader SP-C8 1.296 0.647

Celeston SP-C8 0.676 0.337

Meade SP-C8 0.360 0.180

baader SSC 6" 2.125 1.060

Celeston SSC 6" 1.108 0.553

Meade SSC 6" 0.590 0.295

binos 7.162 3.575

make rings make rings –– live demolive demo

36mm in SP-C8

26mm in SP-C8

18mm in SP-C8

36mm in SSC 6”

26mm in SSC 6”

18mm in SSC 6”

binos Telrad

make rings make rings –– exampleexample

36mm in SP-C8

26mm in SP-C8

18mm in SP-C8

36mm in SSC 6”

26mm in SSC 6”

18mm in SSC 6”

binos Telrad

PowerPoint tipsPowerPoint tips

�� use Shift key to use Shift key to

draw perfect circlesdraw perfect circles

�� check oncheck on

Lock Aspect RatioLock Aspect Ratio

�� enter size with enter size with

two or three digitstwo or three digits

�� follow size figure follow size figure

with units (" or cm)with units (" or cm)

printprint

�� turn off scaling, i.e. turn off scaling, i.e.

print at 100%print at 100%

�� test on paper sheetstest on paper sheets

�� verify scale with chartverify scale with chart

�� final print on final print on

clear acetate filmclear acetate film

other tipsother tips

�� label printout for particular chartlabel printout for particular chart

�� beside circles show mm, TFOV in beside circles show mm, TFOV in °°, x, x

�� include other scaled objectsinclude other scaled objects

–– Moon Moon ½½°°

–– Andromeda 2Andromeda 2½½°°

–– Big Dipper 25Big Dipper 25°°

samplesample

finfin

�� thanksthanks

�� questions?questions?