William Optics SWAN 40mm 2" vs Meade Series 4000 Super Plossl 56mm 2"

[starscy]

Has anyone used long focal length 2" eyepieces such as the William Optics SWAN 40mm or the Meade Series 4000 Super Plossl 56mm with a Newtonian? Both seem capable of producing the same true field of view but how do they perform? Are there any distortions near the edge of the field of view?

[John]

Used with what newtonian ? - the focal ratio will determine which would would best. Genrally for F/5 scopes 32mm is the optimum longest focal length eyepiece otherwise the exit pupil gets too large causing a number of viewing issues.

[starscy]

So neither of the above options would make a good choice for a f/5 Newtonian? To optain the widest field of view and keep distortions to a minimum what would be the best eyepiece under £100?

[John]

So neither of the above options would make a good choice for a f/5 Newtonian? To optain the widest field of view and keep distortions to a minimum what would be the best eyepiece under £100?

Thats a tough set of criteria !.

I know that Astro Baby uses a 38mm Skywatcher Panaview with her F/5 newt and enjoys it a lot. They cost £85 from First Light Optics. They are not aberration free right to the edge of course but are probably as good as it gets for under £100.

[starscy]

The Sky-Watcher Panaview eyepieces seem to have the same specifications as the older Sky-Watcher SWA. The only difference appears to be the eyepiece construction. Anyone else noticed this?

[michael.h.f.wilkinson]

A 40 mm would be OK in an F/5 if you are young enough to have an 8mm fully dilated pupil (like my kids). As we grow older pupils dilate to no more than 5-6mm, so 25-30mm is the largest usable. The TMB Paragon 30mm should be of interest, its getting the same kind of review as my 40mm (I have an F/10 scope so it gives a 4mm exit pupil), which has very low distortion, and is very well-corrected. My experience with a 22mm Nagler and 14 mm UWA suggests that even for terrestrial observation, these ultra-wides have tollerable pin-cushion distortion. For astronomical work, it is of no concern to me. The Nagler 31mm would then spring to mind (it is currently being discussed in another thread.

[Doc]

On Friday night I borrowed a old Meade 50mm 2" eyepiece and used in in my F4.5 dob, I was amazed at the fov and the clarity. The eyepiece felt very comfortable to use, and only a little coma was detected.

[michael.h.f.wilkinson]

On Friday night I borrowed a old Meade 50mm 2" eyepiece and used in in my F4.5 dob, I was amazed at the fov and the clarity. The eyepiece felt very comfortable to use, and only a little coma was detected.

This does give you a 11mm exit pupil, so quite a bit of your aperture is unused. The light from the outer (expensive and heavy) inches of the aperture will be projected outside of your pupil, and will not reach your retina. If you are my age, with a 5-6 mm pupil, the effect is of halving the diameter of your telescope, and thus losing 75% of the light. Even with a youngster's pupil of 8 mm, almost half the light is being lost.

The comfort probably stems from the fact that moving your eye around a bit keeps you inside this massive exit pupil.

[Doc]

This does give you a 11mm exit pupil, so quite a bit of your aperture is unused. The light from the outer (expensive and heavy) inches of the aperture will be projected outside of your pupil, and will not reach your retina. If you are my age, with a 5-6 mm pupil, the effect is of halving the diameter of your telescope, and thus losing 75% of the light. Even with a youngster's pupil of 8 mm, almost half the light is being lost.

The comfort probably stems from the fact that moving your eye around a bit keeps you inside this massive exit pupil.

I know exactly what you are saying and I was very surprised, I really thought before I used it that this would not work, but I was pleasently surprised.