In this episode of Telescope Tips, Brian Hancock and Jeremy Veldman present some cost effective eyepiece options. Premium eyepieces like the 31mm Nagler can be expensive, these eyepieces perform very well and are budget friendly. Also, Brian discusses why Exit Pupil, NOT magnification, is important when choosing eyepieces.
Terminology
- Apparent Field of View (AFOV)
- Eye Relief (ER)
- Focal Length
- Scope Focal Ratio (f/number)
- Exit Pupil
The exit pupil is the bright circle that can be seen in the center of each eyepiece.
The focal length is simply the effective distance from the lens or mirror to the focal point, where an eyepiece or camera would go.
Scope Focal Ratio (f/number): A lens or mirror's focal length divided by its aperture. For instance, a telescope with an 80-mm-wide lens and a 400-mm focal length has a focal ratio of f/5.
To calculate exit pupil, divide the eyepiece focal length by the telescope’s focal ratio. A longer focal length eyepiece will giver you a bigger exit pupil and therefore a brighter view. A shorter focal length eyepiece will give you a smaller exit pupil and therefore a dimmer view. Going below a 1.5mm-1.8mm exit pupil (except for compact planetary nebulae, binary stars, globular clusters and, of course, planets) may not give the best view of extended deep sky objects like galaxies and nebulae. Therefore, it is best to consider exit pupil as opposed to magnification when selecting an eyepiece.
Eyepieces
- Televue 32mm plossl, 22mm ER, 50deg AFOV, cost ~$147
- Agena 25mm, 20mm ER, 60deg AFOV, cost ~$60
- APM 18mm Ultra Flat Field (UFF), 20mm ER, 65deg AFOV, cost ~$130
- Morpheus 9mm, 21mm ER, 76deg AFOV, cost ~$239
- Meade UWA 5.5mm, 13mm ER, 82deg AFOV, cost ~129
Sources:
imaging.nikon.com/lineup/spor...
starizona.com/tutorial/which-...
skyandtelescope.org/observing...
www.eyepiecesetc.com/
www.cloudynights.com/
2019 Eyepieces Buyers Guide by Don Pensack-
Download HERE- bit.ly/30Awzd9
Clear Skies!!