Sky-Watcher Ultrawide Eyepiece Series?

[John]

Oddly, I have two Celestron 6mm Plossls that came in different sets, it's highly unlikely I'll try them in the bino lol! I think with Plossls at least, 8mm is the smallest usable focal length.

I think it depends on how short eye relief you can tolerate and the ergonomics of the eyecup / eyepiece top.

Many of the highest rated planetary eyepieces have short eye relief but their owners get used to this and are happy to accept it in return for the needle sharp, high contrast, low scatter views.

Personally I do prefer something with a little more eye relief these days though - must be getting soft in my old age !

[Mak the Night]

I think it depends on how short eye relief you can tolerate and the ergonomics of the eyecup / eyepiece top.

Many of the highest rated planetary eyepieces have short eye relief but their owners get used to this and are happy to accept it in return for the needle sharp, high contrast, low scatter views.

Personally I do prefer something with a little more eye relief these days though - must be getting soft in my old age !

It is subjective I suppose, I can deal quite happily with the 10mm ER of my 15mm TV Plossl and 16mm Nagler, although my preferred eye relief, or at least that which I find most comfortable, is somewhere around 13mm. The 8 and 11mm TV Plossls are usable to me however. 

I couldn't get used to the 6mm Celestron Plossls and have hardly ever used them. These Celestron 6mm Plossls (below) don't even appear to have the same physical dimensions.

Eyepiece ergonomics and design is another thing I find weird. Below are four individual eyepieces that I have considered to acquire two of for use in the bino. 

From left to right they are a: 15mm TV Plossl, 15mm Celestron 'Kellner', 15mm Celestron Omni Plossl and a bog standard Celestron 17mm Plossl. The Kellner easily has the largest field stop and AFOV. The 15mm and 17mm Celestron Plossls are physically almost identical with incredibly similar subjective lenses, eye relief, field stops and AFOV. The TeleVue appears to have a very slightly smaller field stop and AFOV and has a 10mm ER. I compared all of these in the same telescope in daylight conditions viewing the same target (a distant church steeple). The TV, unsurprisingly, gave the sharpest and brightest image. Although the Celestron Plossls gave good images, the 15mm gave a slightly smaller/less magnified one than the TeleVue of equal focal length! The Kellner image was about the same size as the Omni 15mm although having more AFOV it was difficult to compare. The eye relief on the 15mm Celestron Plossl is 13mm and it seems to be the same on the 17mm Celestron Plossl. The size of the image with the 15mm Omni was bigger than the 17mm, as would be expected, but smaller than the 15mm TV and seemed to be mid way between them. Ergonomics is weird!

The Omni was in the running for being chosen to make a bino pair for a while, but the TeleVue won. They are both nice eyepieces though. 

[John]

Interesting stuff

[Mak the Night]

Right, next step, binoviewer!