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Eyepiece Calculator
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Follow the steps below to see the eyepiece table.
Initial Conditions
| Focal Length: | 660.0mm |
| Aperture: | 127.0mm |
| Focal Ratio: | 5.2 |
| Include 2-inch data: | True |
| Table corrected for Paracorr: | False |
| List only DIOPTRX eyepieces: | False |
| Max recommended mag. for aperture: | 300x |
NP-127is
| 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) |
| Panoptic | 41 | 68 | 27 | 2" | 16.1 | 7.9* | 4.0 | 956 | 209.1 | -- | 32.2 | -- | -- | 64.4 | -- |
| Plössl | 55 | 50 | 38 | 2" | 12.0 | 10.6* | 4.0 | 956 | 209.1 | -- | 24.0 | -- | -- | 48.0 | -- |
| Nagler 5 | 31 | 82 | 19 | 2" | 21.3 | 6.0 | 3.6 | 873 | 190.9 | -- | 42.6 | -- | -- | 85.2 | -- |
| Panoptic | 35 | 68 | 24 | 2" | 18.9 | 6.7 | 3.4 | 804 | 175.9 | -- | 37.7 | -- | -- | 75.4 | -- |
| Ethos | 21 | 100 | 15 | 2" | 31.4 | 4.0 | 3.1 | 752 | 164.5 | -- | 62.9 | -- | -- | 125.7 | -- |
| Nagler 4 | 22 | 82 | 19 | 2" | 30.0 | 4.2 | 2.7 | 646 | 141.4 | -- | 60.0 | -- | -- | 120.0 | -- |
| Panoptic | 27 | 68 | 19 | 2" | 24.4 | 5.2 | 2.6 | 634 | 138.6 | -- | 48.9 | -- | -- | 97.8 | -- |
| Ethos | 17 | 100 | 15 | 2" | 38.8 | 3.3 | 2.6 | 615 | 134.5 | -- | 77.6 | -- | -- | 155.3 | -- |
| Panoptic | 24 | 68 | 15 | 1¼" | 27.5 | 4.6 | 2.3 | 561 | 122.7 | 55.0 | 55.0 | 68.8 | 82.5 | 110.0 | 137.5 |
| Plössl | 32 | 50 | 22 | 1¼" | 20.6 | 6.2 | 2.3 | 561 | 122.7 | 41.3 | 41.3 | 51.6 | 61.9 | 82.5 | 103.1 |
| Plössl | 40 | 43 | 28 | 1¼" | 16.5 | 7.7* | 2.3 | 561 | 122.7 | 33.0 | 33.0 | 41.3 | 49.5 | 66.0 | 82.5 |
| Ethos | 13 | 100 | 15 | 2" & 1¼" | 50.8 | 2.5 | 1.9 | 463 | 101.4 | 101.5 | 101.5 | 126.9 | 152.3 | 203.1 | 253.8 |
| Nagler 5 | 16 | 82 | 10 | 1¼" | 41.3 | 3.1 | 1.9 | 459 | 100.5 | 82.5 | 82.5 | 103.1 | 123.8 | 165.0 | 206.3 |
| Panoptic | 19 | 68 | 13 | 1¼" | 34.7 | 3.7 | 1.8 | 443 | 96.8 | 69.5 | 69.5 | 86.8 | 104.2 | 138.9 | 173.7 |
| Delos | 17.3 | 72 | 20 | 1¼" | 38.2 | 3.3 | 1.8 | 441 | 96.4 | 76.3 | 76.3 | 95.4 | 114.5 | 152.6 | 190.8 |
| Plössl | 25 | 50 | 17 | 1¼" | 26.4 | 4.8 | 1.8 | 441 | 96.4 | 52.8 | 52.8 | 66.0 | 79.2 | 105.6 | 132.0 |
| DeLite | 18.2 | 62 | 20 | 1¼" | 36.3 | 3.5 | 1.7 | 397 | 86.8 | 72.5 | 72.5 | 90.7 | 108.8 | 145.1 | 181.3 |
| Ethos | 10 | 100 | 15 | 2" & 1¼" | 66.0 | 1.9 | 1.5 | 368 | 80.5 | 132.0 | 132.0 | 165.0 | 198.0 | 264.0 | 330.0† |
| Nagler 6 | 13 | 82 | 12 | 1¼" | 50.8 | 2.5 | 1.5 | 366 | 80.0 | 101.5 | 101.5 | 126.9 | 152.3 | 203.1 | 253.8 |
| Delos | 14 | 72 | 20 | 1¼" | 47.1 | 2.7 | 1.5 | 359 | 78.6 | 94.3 | 94.3 | 117.9 | 141.4 | 188.6 | 235.7 |
| Plössl | 20 | 50 | 14 | 1¼" | 33.0 | 3.8 | 1.5 | 355 | 77.7 | 66.0 | 66.0 | 82.5 | 99.0 | 132.0 | 165.0 |
| DeLite | 15 | 62 | 20 | 1¼" | 44.0 | 2.9 | 1.4 | 332 | 72.7 | 88.0 | 88.0 | 110.0 | 132.0 | 176.0 | 220.0 |
| Delos | 12 | 72 | 20 | 1¼" | 55.0 | 2.3 | 1.3 | 312 | 68.2 | 110.0 | 110.0 | 137.5 | 165.0 | 220.0 | 275.0 |
| Ethos | 8 | 100 | 15 | 2" & 1¼" | 82.5 | 1.5 | 1.2 | 289 | 63.2 | 165.0 | 165.0 | 206.3 | 247.5 | 330.0† | 412.5† |
| DeLite | 13 | 62 | 20 | 1¼" | 50.8 | 2.5 | 1.2 | 287 | 62.7 | 101.5 | 101.5 | 126.9 | 152.3 | 203.1 | 253.8 |
| Delos | 10 | 72 | 20 | 1¼" | 66.0 | 1.9 | 1.1 | 264 | 57.7 | 132.0 | 132.0 | 165.0 | 198.0 | 264.0 | 330.0† |
| Plössl | 15 | 50 | 10 | 1¼" | 44.0 | 2.9 | 1.1 | 262 | 57.3 | 88.0 | 88.0 | 110.0 | 132.0 | 176.0 | 220.0 |
| Nagler 6 | 9 | 82 | 12 | 1¼" | 73.3 | 1.7 | 1.1 | 258 | 56.4 | 146.7 | 146.7 | 183.3 | 220.0 | 293.3 | 366.7† |
| DeLite | 11 | 62 | 20 | 1¼" | 60.0 | 2.1 | 1.0 | 243 | 53.2 | 120.0 | 120.0 | 150.0 | 180.0 | 240.0 | 300.0 |
| Ethos | 6 | 100 | 15 | 2" & 1¼" | 110.0 | 1.2 | 0.90 | 216 | 47.3 | 220.0 | 220.0 | 275.0 | 330.0† | 440.0† | 550.0† |
| Delos | 8 | 72 | 20 | 1¼" | 82.5 | 1.5 | 0.86 | 206 | 45.0 | 165.0 | 165.0 | 206.3 | 247.5 | 330.0† | 412.5† |
| Nagler 6 | 7 | 82 | 12 | 1¼" | 94.3 | 1.3 | 0.84 | 202 | 44.1 | 188.6 | 188.6 | 235.7 | 282.9 | 377.1† | 471.4† |
| DeLite | 9 | 62 | 20 | 1¼" | 73.3 | 1.7 | 0.83 | 199 | 43.6 | 146.7 | 146.7 | 183.3 | 220.0 | 293.3 | 366.7† |
| Plössl | 11 | 50 | 8 | 1¼" | 60.0 | 2.1 | 0.79 | 189 | 41.4 | 120.0 | 120.0 | 150.0 | 180.0 | 240.0 | 300.0 |
| Ethos SX | 4.7 | 110 | 15 | 2" & 1¼" | 140.4 | 0.90 | 0.78 | 186 | 40.6 | 280.9 | 280.9 | 351.1† | 421.3† | 561.7† | 702.1† |
| Delos | 6 | 72 | 20 | 1¼" | 110.0 | 1.2 | 0.66 | 158 | 34.5 | 220.0 | 220.0 | 275.0 | 330.0† | 440.0† | 550.0† |
| DeLite | 7 | 62 | 20 | 1¼" | 94.3 | 1.3 | 0.65 | 156 | 34.1 | 188.6 | 188.6 | 235.7 | 282.9 | 377.1† | 471.4† |
| Ethos SX | 3.7 | 110 | 15 | 2" & 1¼" | 178.4 | 0.71 | 0.61 | 146 | 32.0 | 356.8† | 356.8† | 445.9† | 535.1† | 713.5† | 891.9† |
| Nagler 6 | 5 | 82 | 12 | 1¼" | 132.0 | 0.96 | 0.61 | 145 | 31.8 | 264.0 | 264.0 | 330.0† | 396.0† | 528.0† | 660.0† |
| Plössl | 8 | 50 | 6 | 1¼" | 82.5 | 1.5 | 0.56 | 135 | 29.5 | 165.0 | 165.0 | 206.3 | 247.5 | 330.0† | 412.5† |
| Delos | 4.5 | 72 | 20 | 1¼" | 146.7 | 0.87 | 0.49 | 116 | 25.5 | 293.3 | 293.3 | 366.7† | 440.0† | 586.7† | 733.3† |
| DeLite | 5 | 62 | 20 | 1¼" | 132.0 | 0.96 | 0.46 | 110 | 24.1 | 264.0 | 264.0 | 330.0† | 396.0† | 528.0† | 660.0† |
| Nagler Zoom | 6 - 3 | 50 | 10 | 1¼" | 110.0 - 220.0 | 1.2 - 0.58 | 0.44 - 0.23 | 106 - 54 | 23.2 - 11.8 | 220.0 - 440.0† | 220.0 - 440.0† | 275.0 - 550.0† | 330.0† - 660.0† | 440.0† - 880.0† | 550.0† - 1,100.0† |
| Nagler 6 | 3.5 | 82 | 12 | 1¼" | 188.6 | 0.67 | 0.42 | 100 | 21.8 | 377.1† | 377.1† | 471.4† | 565.7† | 754.3† | 942.9† |
| Delos | 3.5 | 72 | 20 | 1¼" | 188.6 | 0.67 | 0.38 | 91 | 20.0 | 377.1† | 377.1† | 471.4† | 565.7† | 754.3† | 942.9† |
| DeLite | 4 | 62 | 20 | 1¼" | 165.0 | 0.77 | 0.37 | 89 | 19.5 | 330.0† | 330.0† | 412.5† | 495.0† | 660.0† | 825.0† |
| DeLite | 3 | 62 | 20 | 1¼" | 220.0 | 0.58 | 0.28 | 66 | 14.5 | 440.0† | 440.0† | 550.0† | 660.0† | 880.0† | 1,100.0† |
| 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.