Right eyepeice for the scope (14" f4.5)?

[boboco]

Hi,

I have what I thought was a good selection of eye peices for my Orion Optics OD350 f4.5 14" dob.

Primarily for wide field viewing I have a 28mm Skywatcher Nirvana UWA 2" which seemed to get very good reviews and I had been very pleased with (whole of the beehive, whole of the double cluster in FOV) .... until I tried some other eyepieces with the help of Hants Astro.

Compared to a Zhumell 28mm 2" the UWA was very "soft", the Zhumell gave more pinpoint stars. Colimation was good, seeing was okay and I exchanged eye peices a few times to average out any poor seeing.

So what could be wrong? Why is one crisp and one soft? Could it be a focus issue, is the UWA somehow stuck with a smaller focal sweet spot that I failed to hit? Is this just the price I pay for such a huge field of view?

I really want to figure out how to make sure any future eye peice purchases avoid types which dont suit my scope.

(I also tried a Skywatcher Panoptic, which was not as good as the UWA in my very humble opinion at least).

Thanks to Dave at Hants Astro and the other person whos name I have forgotten for the try of the Panaview (thanks for the correction jahmanson!) and Baader Clickstop - which was surprisingly very nice (especially since I have been put off of variable eye pieces by generally poor reviews).

Cheers,

Karl.

[John]

I'm really surprised to be honest Karl. I've tested a 28mm Nirvana against my Nagler 31mm and it came very close indeed to the performance of the Nagler in the 12" F/5 dobsonian that I had at the time.

I've read a bit about the performance of various Zhumell eyepieces and, while decent for price, they don't seem to be in the same league as the Nirvana.

I'm going to take a guess here - did the Zhumell have a narrower field of view than the Nirvana's 82 degrees ?. If so, then I reckon it could be coma that you are seeing in the wider field Nirvana - coma is produced by fast newtonians but sometimes is only apparent when a quality wide field eyepiece is used.

It may well be that you need to consider a coma corrector for use with your 14" F/4.5 scope.

FWIW I think you meant the Skywatcher Panaview - the Panoptic is a Tele Vue eyepiece.

[boboco]

I'm really surprised to be honest Karl. I've tested a 28mm Nirvana against my Nagler 31mm and it came very close indeed to the performance of the Nagler in the 12" F/5 dobsonian that I had at the time.

I've read a bit about the performance of various Zhumell eyepieces and, while decent for price, they don't seem to be in the same league as the Nirvana.

Well quite, that was pretty much my reaction.

I'm going to take a guess here - did the Zhumell have a narrower field of view than the Nirvana's 82 degrees ?. If so, then I reckon it could be coma that you are seeing in the wider field Nirvana - coma is produced by fast newtonians but sometimes is only apparent when a quality wide field eyepiece is used.

It may well be that you need to consider a coma corrector for use with your 14" F/4.5 scope.

Yes, definitely a smaller fov.

FWIW I think you meant the Skywatcher Panaview - the Panoptic is a Tele Vue eyepiece.

corrected - thanks