Quote:
Originally Posted by torr
My primary mirror was slightly pinched , after re-adjusting the clamp tension and re-collimation the defocused star patterns are almost perfect and hold now, to my eyes anyway.
When I said I tightened the clamps the other night, it was't very much so I was surprised it had such an effect on the primary 
Thanks for that.
I managed too see the cassini division last night for the 1st time using the 17mm stratus (88*) although seeing was far from optimal.
I really am liking the goto system, its making this hobby so much more enjoyable , I must admit I am bit impatient, and the goto helps here a lot.
I would love a wider field lower mag eyepiece but Ill have to be content with what I have for now.
My comment on the 32mm TV was not clear sorry.
I was meaning the 24mm stratus gives brighter views and similar if not slightly bigger field of view then my 32mm TV plossl making the TV obsolete.
I see the 35mm Pano in the classifieds. I am a bit reluctant with 35mm and over as the exit pupil concerns me as it will be over 7mm according to the teleview charts , something I'd like to test before shelling out for it.
I read the 31mm Nag is around 6.3mm exit pupil and the true field is around 1.6 deg
Cheers
James |
f.l. = 1500mm, f4.9
The 35mm Panoptic has a field stop diameter of 38.7mm. This will give you a true field of TFOV= FSD*57.3/f.l. = 38.7*57.3/1500 = 1.5 deg. Exit pupil = 35/4.9 = 7.1mm. With Paracorr TFOV=1.5/1.15 = 1.3 deg. Exit pupil = 7.1/1.15 = 6.2mm.
The 31mm Type 5 Nagler has a field stop diameter of 42mm. This will give you a true field of 1.6 deg. Exit pupil = 6.3mm. With Paracorr TFOV = 1.4 deg. Exit pupil = 5.5mm.
The 26mm Type 5 Nagler has a field stop diameter of 35mm. This will give you a true field of 1.3 deg. Exit pupil = 5.3mm. With Paracorr TFOV = 1.2 deg. Exit pupil = 4.6mm.
The 21mm Ethos has a field stop diameter of 36.2mm. This will give you a true field of 1.4 deg. Exit pupil = 4.3mm. With Paracorr TFOV = 1.2 deg. Exit pupil = 3.7mm.
A Paracorr acts as a 1.15x Barlow and corrects for primary mirror coma. I have rounded the above numbers.
I think the 31mm Nagler is useable under dark skies but also especially when combined with an O-III filter for some spectacular views of the larger nebulae.
The 26mm Nagler may be a better choice than the 31mm Nagler but note it has a little less eye relief. The 21mm Ethos a little less again but adequate I would think without glasses.
Eye relief:
35Pan = 24mm
31NT5 = 19mm
26NT5 = 16mm
21NT5 = 15mm
I would consider the eye relief of the 35 Pan very comfortable, 31mm Nagler comfortable, 26mm Nagler adequate and I have not used the 21 Ethos. I do not wear glasses.
The 21mm Ethos has a slightly wider true field than the 26mm Nagler and smaller exit pupil. It would be ideal for you telescope, but not quite wide enough for the full Pleiades and for that you need the 41mm Panoptic with 46mm field stop diameter for a 1.8 degree true field but at 8.3mm exit pupil. You will effectively be losing some light due to the large exit pupil but if you have dark skies it really doesn't matter since you have plenty of aperture to play with and you are using the eyepiece for it's maximum true field capability.
The use of the Paracorr is a personal choice and some people don't like coma and others are not bothered by it.
If you can go to a star party and get to try some or all of the above eyepieces and/or Paracorr only then you will know which is best for you. I think the darker background will be more pleasing which the 21mm Ethos will give you.
See
http://www.televue.com/engine/TV3b_p...4#.U6uMDZSSy5I for Tele Vue eyepiece specifications.