shneor
October 8th, 2012, 10:42 PM
I spent a few months considering this purchase, but I finally went for it: the new Explore Scientific 9mm 120°, weighing in at almost 3 pounds. Advertised at $999, it cost me "only" $949 from Astronomics, as I'm a Cloudy Nights member. I tried it out first in my back yard, in a 10" f/5 newt, then last Saturday night at Blue Canyon, in my 22" f/4, when I observed with Alvin Huey.
This eyepiece is advertised as having a 120° apparent field. That's just not true, as the apparent field is more like 140°. Using bright stars in the Pleiades, I compared the field to that of my 13mm Ethos. The Ethos' field was just maybe 2-3% wider, if that. But even more surprising was that stars is this eyepiece are pinpoint to the edge - at f/4. And not only stars; Jupiter's shape was undistorted at the edge, and at least 3 bands were still distinctly visible (Jupiter was about 20° above the horizon). There was lateral color in about the outer 15-18% of the field, but that's not visible with stars or DSOs. Stars on the edge dissolve into a blue-violet blur, but that's stars literally going out of the field. Not that you can see the entire field (not yet for me, anyway) without turning your head. Also, the weight of this eyepiece demands extra care in handling, and additional weight at the lower end of my telescope.
I did some comparisons to the 9mm ES100°. My impression was that the view was a bit sharper and more contrasty in the 120, and that there was a bit more light throughput; I tested on a "vertical" dark lane in M82, and a dust lane in M31. I had a couple of spectacular views - M8 (using an NPB filter) filled the field, but the field encompassed all the visible nebulosity. The Perseus galaxy cluster was edge-to-edge with a line of galaxies.
I'm a bit puzzled as to why this eyepiece is advertised as having a 120° apparent field, when it's really about 140°. Also, in the daytime when you look to the edge of the field, there's a very thin blue-green ring at the extreme edge of the field. My speculation is that the eyepiece was designed for 120°, but the view was so good in the outer 10°, they decided to leave the field stop off (the edge of the field is sharp, however).
I'd say that Al Nagler has some serious catching up to do.
This eyepiece is advertised as having a 120° apparent field. That's just not true, as the apparent field is more like 140°. Using bright stars in the Pleiades, I compared the field to that of my 13mm Ethos. The Ethos' field was just maybe 2-3% wider, if that. But even more surprising was that stars is this eyepiece are pinpoint to the edge - at f/4. And not only stars; Jupiter's shape was undistorted at the edge, and at least 3 bands were still distinctly visible (Jupiter was about 20° above the horizon). There was lateral color in about the outer 15-18% of the field, but that's not visible with stars or DSOs. Stars on the edge dissolve into a blue-violet blur, but that's stars literally going out of the field. Not that you can see the entire field (not yet for me, anyway) without turning your head. Also, the weight of this eyepiece demands extra care in handling, and additional weight at the lower end of my telescope.
I did some comparisons to the 9mm ES100°. My impression was that the view was a bit sharper and more contrasty in the 120, and that there was a bit more light throughput; I tested on a "vertical" dark lane in M82, and a dust lane in M31. I had a couple of spectacular views - M8 (using an NPB filter) filled the field, but the field encompassed all the visible nebulosity. The Perseus galaxy cluster was edge-to-edge with a line of galaxies.
I'm a bit puzzled as to why this eyepiece is advertised as having a 120° apparent field, when it's really about 140°. Also, in the daytime when you look to the edge of the field, there's a very thin blue-green ring at the extreme edge of the field. My speculation is that the eyepiece was designed for 120°, but the view was so good in the outer 10°, they decided to leave the field stop off (the edge of the field is sharp, however).
I'd say that Al Nagler has some serious catching up to do.