Calculator
Eyepiece Calculator
TeleVue.com: Article > Calculator
Input Box
Follow the steps below to see the eyepiece table.
(1) Enter any 2 of the 3 parameters for your telescope
... or Recall a Stored Run
(2a) Choose telescope eyepiece preferences
(2b) Limit to these eyepieces
Current: 
Discontinued: 
(3) Enter optional run name and select table presentation order
True Field: Listed from wide to narrow. Eps with same field sort higher mag first.
Magnification: Listed from low to high. Eps with same mag sort wider field first.
Design: Listed from narrow to wide field designs and zooms last.
Note: Zooms sort based on low-power specification.
(4) Calculate Results
Initial Conditions
Focal Length: 600.0mm
Aperture: 120.0mm
Focal Ratio: 5.0
Include 2-inch data: False
Table corrected for Paracorr: False
List only DIOPTRX eyepieces: False
Max recommended mag. for aperture: 283x

d:120mm, f:600mm
UP

DesignFocal
Length
(mm)
Apparent
Field
(°)
Eye
Rel.
(mm)
Barrel
Size
Mag.
(x)
Exit
Pupil
(mm)
True
Field
(°)
True
Field
@
1000
yards
(feet)
Mag.
w/2x
Barlow
(2x)
Mag.
w/2x
Big Barlow
or
Power-
mate
(2x)
Mag.
w/2.5x
Power-
mate
(2.5x)
Mag.
w/3x
Barlow
(3x)
Mag.
w/4x
Power-
mate
(4x)
Mag.
w/5x
Power-
mate
(5x)
 Plössl  55  50  38  2"  --  --  --  --  --  --  --  --  --  -- 
 Plössl  32  50  22  1¼"  18.8  6.4  2.6  135.0  37.5  --  46.9  56.3  --  93.8 
 Plössl  40  43  28  1¼"  15.0  8.0*  2.6  135.0  30.0  --  37.5  45.0  --  75.0 
 Plössl  25  50  17  1¼"  24.0  5.0  2.0  106.0  48.0  --  60.0  72.0  --  120.0 
 Plössl  20  50  14  1¼"  30.0  4.0  1.6  85.5  60.0  --  75.0  90.0  --  150.0 
 Plössl  15  50  10  1¼"  40.0  3.0  1.2  63.0  80.0  --  100.0  120.0  --  200.0 
 Plössl  11  50  8  1¼"  54.5  2.2  0.87  45.5  109.1  --  136.4  163.6  --  272.7 
 Plössl  8  50  6  1¼"  75.0  1.6  0.62  32.5  150.0  --  187.5  225.0  --  375.0 
DesignFocal
Length
(mm)
Apparent
Field
(°)
Eye
Rel.
(mm)
Barrel
Size
Mag.
(x)
Exit
Pupil
(mm)
True
Field
(°)
True
Field
@
1000
yards
(feet)
Mag.
w/2x
Barlow
(2x)
Mag.
w/2x
Big Barlow
or
Power-
mate
(2x)
Mag.
w/2.5x
Power-
mate
(2.5x)
Mag.
w/3x
Barlow
(3x)
Mag.
w/4x
Power-
mate
(4x)
Mag.
w/5x
Power-
mate
(5x)
Table Notes

For further reading, see Eyepieces Advice.

Tele Vue recommends maximum magnification of 60x / inch (2.5x / mm) of telescope aperture and 350x maximum regardless of aperture.
*An exit pupil greater than 7.5-mm may be too big for a telescope with central obstruction (most reflectors). Conversely, small exit pupils may reveal eyesight defects such as floaters. Consider binocular viewing to diminish the effect of an eye having floaters.

Copyright © 2003-2020 Tele Vue Optics, Inc., 32 Elkay Dr, Chester, NY, 10918 · Call for advice: 1-845-469-4551 (9am-5pm ET) · Privacy Policy