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Calculator
Eyepiece Calculator
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TeleVue.com: Article > Calculator |
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Follow the steps below to see the eyepiece table.
Initial Conditions
| Focal Length: | 1,200.0mm |
| Aperture: | 254.0mm |
| Focal Ratio: | 4.7 |
| Include 2-inch data: | False |
| Table corrected for Paracorr: | False |
| List only DIOPTRX eyepieces: | False |
| Max recommended mag. for aperture: | 350x |
d:254mm, f:1200mm
| Design | Focal Length (mm) | Apparent Field (°) | Eye Rel. (mm) | Barrel Size | Mag. (x) | Exit Pupil (mm) | True Field (°) | Star Drift Time (sec) | 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" | 37.5 | 6.8 | 1.3 | 309 | 67.5 | 75.0 | -- | 93.8 | 112.5 | -- | 187.5 |
| Plössl | 40 | 43 | 28 | 1¼" | 30.0 | 8.5* | 1.3 | 309 | 67.5 | 60.0 | -- | 75.0 | 90.0 | -- | 150.0 |
| Plössl | 25 | 50 | 17 | 1¼" | 48.0 | 5.3 | 1.0 | 242 | 53.0 | 96.0 | -- | 120.0 | 144.0 | -- | 240.0 |
| Plössl | 20 | 50 | 14 | 1¼" | 60.0 | 4.2 | 0.82 | 195 | 42.8 | 120.0 | -- | 150.0 | 180.0 | -- | 300.0 |
| Plössl | 15 | 50 | 10 | 1¼" | 80.0 | 3.2 | 0.60 | 144 | 31.5 | 160.0 | -- | 200.0 | 240.0 | -- | 400.0† |
| Plössl | 11 | 50 | 8 | 1¼" | 109.1 | 2.3 | 0.43 | 104 | 22.8 | 218.2 | -- | 272.7 | 327.3 | -- | 545.5† |
| Plössl | 8 | 50 | 6 | 1¼" | 150.0 | 1.7 | 0.31 | 74 | 16.3 | 300.0 | -- | 375.0† | 450.0† | -- | 750.0† |
| Design | Focal Length (mm) | Apparent Field (°) | Eye Rel. (mm) | Barrel Size | Mag. (x) | Exit Pupil (mm) | True Field (°) | Star Drift Time (sec) | 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.