SkyWatcher Ultrawide Eyepieces

[jnp]

I am tempted with the SkyWatcher 6mm Ultrawide Eyepiece. On paper they seem very good value under £40 with a 68 degree FOV and good eye refief. Has anyone any experience using these and how do they compare with say standard plossls?

[John]

I think they are 66 degrees FoV and OK with scopes of F/7 or longer focal ratio. The 9mm is supposed to be the best one of the four in the range (20mm, 15mm, 9mm and 6mm) but the 6mm was not bad when I had one a while back.

Compared with a "standard plossl" their longer eye relief is probably their best feature.

John

[John]

Duplicate post to the one above - how did I do that ????

Mods - please delete this one.

Thanks,

John

[jnp]

Thanks for info regarding suitability only for f7 or faster scopes. I cant see that in any descriptions.

What would it be like on my f5. I assume that the 66 fov wont all be useable as I would get distortion at the edges?

[johninderby]

Hi

The 6mm and 9mm are a different design internally to the 15mm and 20mm. The 6mm and 9mm do tend to suffer from the "kidney bean" effect and don't work that well in faster scopes. The design of the 15mm and 20mm is a bit more forgiving and can work in a faster scope.

John

[WWPierre]

Dredging up this old thread. I just received a clone of the 6mm from a chap in central China. It cost me about $30 CDN delivered to my PO Box. It did take a month and a half to get here.

Anyway, I tried it out during the day on my 5" F/5 Heritage collapsible dob, my Celestron Nexstar 80 (F/5 as well), and my 90mm F13 Seben Mak clone.

One must consider that the top end of the optical chain consists of a 65 year old astigmatic eyeball behind corrective lenses.

The views through all 3 scopes was pretty similar, with the 5" dob being brighter as expected. I was surprised to see a bit of kidney beaning around the edge in all 3 scopes. The focal length didn't seem to matter, and the KB disappeared in all cases with correct eye placement. The sweet spot for this was quite small.

I estimate my eyeball to be about half an inch from the outside surface of my spectacles, and I could rest my glasses on the turned-down rubber eyecup and see the field stop all around, so the eye-relief specs seem to be fairly close.

I had no plossl of similar F/L to compare, but this EP was a lot more comfortable than my hardly ever used 4mm plossl. It was also a lot more comfortable than a barlowed 15mm plossl. I expect it to perform pretty with my Burgess 5" refractor, which has a MoonLite 2 speed focuser, pretty much a necessity to zero in on the minuscule sweet spot presented by single digit F/L EPs.

For the money, I think this is a pretty good EP. Can't wait to try it on Jupiter and Saturn.