Quote:
Originally Posted by The Mekon
Am bumping this old thread along as I am asking a similar question, except substitute 22mm Nagler for 20mm
At present I have an old 2" 32mm Erfle (awful erfle I call it) and don't use it much. Gives 32x and 65 degree field, plenty of distortion at the edges. Thinking that the 27 Panoptic may be too much like this thing. What I love about Naglers is there great views right to the edge.
Good thing about Panoptics, is that its more comfortable to see the edge.
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The 27mm Panoptic is a highly corretced eyepiece, nothing like your 32mm Erfle. The 20mm T2 Nagler is regarded as a very fine eyepiece but it is rather heavy, similar to the 31mm Nagler or 41mm Panoptic. The 20mm T5 Nagler is much lighter and is also highly corrected and an excellent performer.
I'm not sure you can compare the 20mm Nagler T2 or T5 with the 27mm Panoptic since there are too many differences. The field stop diameter of both 20mm Naglers is 27.4mm whereas the 27mm Panoptic is 30.5mm so the true field is larger in the Panoptic with the magnification much lower and exit pupil much higher.
You will not be disappointed with either Nagler or Panoptic and both will be in a completely different ball park to the Erfle which shows considerable abberations off axis and I know because I have a Celestron 2", 32mm Erfle too.
The only abberation you will see with the Tele Vue is coma from your primary mirror should you be using a Newtonian and it is actually a pleasing sight to see coma alone and no astigmatism. Get yourself a Paracorr and coma will be gone too.
If you like 82deg fields go the Nagler otherwise the 68deg field of the Panoptic is quite nice. The 27mm Panoptic and 20mm T5 Nagler weigh about the same and about half that of the 20mm T2 Nagler.
I would go the 20mm T5 Nagler for a bit more magnification and smaller exit pupil than the Pan but the final choice depends on the telescope you are using.