Sky-Watcher Ultrawide (66º AFOV) eyepieces

[enigma]

Has anyone tried the Sky-Watcher Ultrawide (66º AFOV) 1.25" eyepieces available in 20mm, 15mm, 9mm and 6mm focal lengths?

[SiriusB]

Hi enigma,

i used to own all four a few years ago, my first ever wideangle eyepieces & well worth the £40 each i paid.IMO.-i think they're even cheaper these days.

Suprisingly sharp on axis, gets a little bit messy towards the edges.

I still have the 20mm, i would rate them from best to worst:

20mm,9mm,6mm,15mm. I found i got bad reflections off the eye lens on the 15mm version for some reason, hence i wouldn't recommend it, (unless i'm the only one to have had this problem?)

What scope are you planning on using them with? i think they might struggle at below f6ish- Anyone used them on an f5 scope?

Hope that helps a little.

[enigma]

I was thinking of getting some instead of Plossls to use in a f/5 reflector, but maybe I should think again?

[GazOC]

I owned the 6mm and the 9mm a few years back, the 9mm was good the 6mm less so. I wouldn't recommend either for an f5 scope though...

[John]

When I was using F/10 scopes I had these and found they worked well at that focal ratio. I then got an F/5 and, as GazOC suggests, with the exception of the 9mm, they were nowwhere near as good. For some reason the 9mm seems a bit better than the rest. The 20mm in particular was pretty poor in the F/5 - the stars were distorted over the outer 50% of the FoV to an extent that was pretty distracting.

[Hypernova]

I own the 9mm version for use in my f5.9 Skywatcher dob. I find pretty good on axis and not much coma towards the edge, maybe about 80-85% of the field is sharp. Obviously the amount of coma will be different depending on the f/ratio of your scope.

I have used it on the full moon and the eyepiece just about frames it with very little to spare. In this view there is not too much degradation of the detail towards the edge. Colour rendition is good and I haven't noticed any annoying reflections even when viewing the moon.

I like the slightly wider field and is a noticeable improvement on the standard MA's (50 degree AFOV) that were supplied with my scope. I haven't had a chance to try any others as those spaces are filled with other eyepieces at the moment.

Hope this helps.

[griff44]

I've just bought a 6mm one and a GSO barlow so will let you know how i get on, just waiting for clear skies, maybe tonight will be the night, who knows with UK weather??

[John]

... I find pretty good on axis and not much coma towards the edge, maybe about 80-85% of the field is sharp. Obviously the amount of coma will be different depending on the f/ratio of your scope....

I believe it's astigmatism you are seeing - coma is produced by the scope but it's usually masked by the astigmatism introduced by eyepieces. The expensive eyepiece types don't introduce astigmatism so you can then detect the coma - which is where a coma corrector comes in .....

Edit: this website provides a useful explanation of these aberrations:

http://www.umich.edu/~lowbrows/reflections/2007/dscobel.27.html

[griff44]

Interesting stuff!

[Hypernova]

I believe it's astigmatism you are seeing - coma is produced by the scope but it's usually masked by the astigmatism introduced by eyepieces. The expensive eyepiece types don't introduce astigmatism so you can then detect the coma - which is where a coma corrector comes in .....

Edit: this website provides a useful explanation of these aberrations:

Got Aberrations?

Thanks for the link, makes for interesting reading. The effect I am seeing does sound rather like astigmatism rather than coma. Either way it isn't that bad and doesn't detract from the overall view.

The other thing I have noticed though, and have just found the correct term for in the link, is kidney beaning. Bean shaped field blackouts when moving you eye around. I have noticed it in this eyepiece more than others I have tried, still not too bad though. You have to hold you eye in the right position to avoid them and that's where the eyecup comes in. It just requires a little bit of getting used to.

[SiriusB]

Doesn't sound so promising for you then enigma at f5. Can anyone suggest some alternative wideangles that will work ok at f5 then?-without breaking the bank!!

[John]

Doesn't sound so promising for you then enigma at f5. Can anyone suggest some alternative wideangles that will work ok at f5 then?-without breaking the bank!!

Can you define "without breaking the bank !!" ?

[enigma]

For me that would translate to preferably less than £50 since a generic Plossl would cost less, but I know that most people would say that such an eyepiece does not really exist.

[neilm]

Admittedly slightly more than £50 but I use a Meade Series 5000 Super Plossl (20mm) in my F5 scope, very pleased with the results. Currently reduced on FLO to £63....could be worth those few extra pennies.

Neil

[enigma]

But for slightly more one could also get a TV Plossl that I think should be better than a Meade Series 5000.