Ethos
100° & 110° Apparent Field Eyepieces
| 21-mm | |
| Model # | ETH-21.0 |
| Focal Length (mm) | 21 |
| Barrel Size (in.) | 2" |
| Apparent Field (deg.) | 100 |
| Eye Relief (mm) | 15 |
| Weight (lb / oz) | 2.25 / 36.0 |
| Field Stop (mm) | 36.2 |
| Compare to similar focal lengths | |
“You've got very innovative engineers always managing to break the laws of optics. This Ethos is out of this world!”
—J.G., France
The 21mm focal length completes the logical set of 21mm/13mm/8mm and nicely juxtaposes the 17mm/10mm/6mm combination. Each step within these two sets approaches a 3x field area gain. The 21mm's effective field stop diameter is 36.2mm, bringing its true field close to the 35mm Panoptic (38.7mm Field Stop diameter). In an f/4 Dobsonian, the exit pupil is just 5.25mm using the 21mm Ethos instead of 8.75mm with a 35mm Panoptic.
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