janoskiss
04-09-2007, 12:39 PM
20mm (and 30mm) Ultra wide angle eyepiece. Brand new.
$80 pick up or $90 posted in Australia.
This is the 20mm Ultrawide from Bintel (https://www.bintelshop.com.au/Product.aspx?ID=7508) which is the exact same eyepiece as the 30mm Ultrawide from Bintel (https://www.bintelshop.com.au/Product.aspx?ID=7509) with a barlow element screwed onto the barrel. So you're getting 2 EPs in one.
FYI, here is all I know about this EP:
Because of mislabelled packaging I ended up with two of these, so one's got to go.
With the barlow element in place, the 20mm's FOV is in fact not the spec 80 degrees but about 70 - not ultrawide but still a big FOV. Eye relief is greater in 20mm mode (although again the specs do not reflect this fact).
On their own, the 20 and 30mm are great for f/10 and slower scopes such as Cassegrains. They do an okay job as finder EPs in faster newts, depending on your tolerance for aberrations off axis.
However in fast Dobs, the best use for the EP I found is in a long 2" barlow like the Orion Deluxe, where the EP becomes a 70+ degree 12-13mm that is sharp edge to edge even in my f/4.7.
I mostly use my UW 20mm in the 30mm configuration in the long barlow, where it's awesome on deep sky and provides plenty of magnification for lunar viewing while still allowing one to see the whole Moon with ample room to spare (in my 10" f/4.7 and 8" f/6). Awesome for public viewing. And yes it is sharp, colour free at f/4.7 to the edge of a flat 70+ degree field! And the contrast is excellent with no stray light, ghosting or reflections.
Unfortunately the popular GSO 2" barlow will not work anywhere near as well as the Orion Deluxe 2" (aka discontinued UO 2"): at f/4.7 the GSO 2" + UW-30mm combo shows both strong field curvature and astigmatism. But the Deluxe + UW-30mm combo is amazing: will take the challenge to any 12-15mm super or ultrawide EP out there (yes even Naglers!) in any scope.
You can barlow the EP in 20mm configuration (ie with barlow group attached) also for a 70+ degree planetary widefield. Eye relief gets pretty long though which makes this configuration less useful for public viewing unless you add an eyeguard extension. And with the screw on barlow bit you do get some ghosting. A barrel extension between the barlow and the 30mm EP is a better way to gain more magnification. You can take the EP down to 5-6mm this way without compromising optical performance using a ~5" long extension tube.
$80 pick up or $90 posted in Australia.
This is the 20mm Ultrawide from Bintel (https://www.bintelshop.com.au/Product.aspx?ID=7508) which is the exact same eyepiece as the 30mm Ultrawide from Bintel (https://www.bintelshop.com.au/Product.aspx?ID=7509) with a barlow element screwed onto the barrel. So you're getting 2 EPs in one.
FYI, here is all I know about this EP:
Because of mislabelled packaging I ended up with two of these, so one's got to go.
With the barlow element in place, the 20mm's FOV is in fact not the spec 80 degrees but about 70 - not ultrawide but still a big FOV. Eye relief is greater in 20mm mode (although again the specs do not reflect this fact).
On their own, the 20 and 30mm are great for f/10 and slower scopes such as Cassegrains. They do an okay job as finder EPs in faster newts, depending on your tolerance for aberrations off axis.
However in fast Dobs, the best use for the EP I found is in a long 2" barlow like the Orion Deluxe, where the EP becomes a 70+ degree 12-13mm that is sharp edge to edge even in my f/4.7.
I mostly use my UW 20mm in the 30mm configuration in the long barlow, where it's awesome on deep sky and provides plenty of magnification for lunar viewing while still allowing one to see the whole Moon with ample room to spare (in my 10" f/4.7 and 8" f/6). Awesome for public viewing. And yes it is sharp, colour free at f/4.7 to the edge of a flat 70+ degree field! And the contrast is excellent with no stray light, ghosting or reflections.
Unfortunately the popular GSO 2" barlow will not work anywhere near as well as the Orion Deluxe 2" (aka discontinued UO 2"): at f/4.7 the GSO 2" + UW-30mm combo shows both strong field curvature and astigmatism. But the Deluxe + UW-30mm combo is amazing: will take the challenge to any 12-15mm super or ultrawide EP out there (yes even Naglers!) in any scope.
You can barlow the EP in 20mm configuration (ie with barlow group attached) also for a 70+ degree planetary widefield. Eye relief gets pretty long though which makes this configuration less useful for public viewing unless you add an eyeguard extension. And with the screw on barlow bit you do get some ghosting. A barrel extension between the barlow and the 30mm EP is a better way to gain more magnification. You can take the EP down to 5-6mm this way without compromising optical performance using a ~5" long extension tube.