A few months ago, I plopped down $52 for a 20mm Orion Expanse eyepiece. This was partly because I had just gotten a fast focal length telescope, and secondly because I wanted more of a free floating in space feeling. I lack the $200 of disposable cash to buy a Nagler eyepiece, but thought that perhaps a good Erfle might do the job. No doubt many of you are aware of how Erfle's suffer distortion around their edges, but at low magnifications this is supposed to be a good performing eyepiece... or at least that's how Orion describes the Erfle in it's cataloge. Maybe I should have shopped around more, but Orion has always done well by me, so when the local Astronomy shop pulled out an Orion Expanse eyepiece when I asked for an Erfle, I willingly gave up 1/5 of my last paycheck. I use it mostly on my Tasco 4.5 inch 500mm focal telescope, on which it's magnification is no more than 20x. Over the last month or so, I've tried it on a variety of targets including the Moon, the Orion Nebula, the Pleadies, The Rosetta Nebula, and a variety of star clusters. While I enjoyed the luxerious 66 degree field of view, the edges of the view were filled with "seagulls" - the images of stars distorted into V shapes, with the point of the V always pointing twards the center of the image. On the other hand, the eye relief was very comfortable, and the image in the center of the field of view is quite sharper than any of my Kellner or Plossl eyepieces. For the sake of comparison, I will try to give a rough idea of how it competed with other eyepieces I own: vs. GTO 30mm Plossl The GTO Plossl provides nearly as sharp an image as the Expanse, though it has a bit more contrast. Though the field of view on this Plossl is noticeably less, it's less magnification more than makes up for it. vs. Orion 25mm Explorer II (Kellner) The Explorer II has a field of view of around 60 degrees, approaching that of the Erfle. The image in this eyepiece is just as sharp as my GTO Plossl, and again compares favorably to the Orion Expanse. It's slightly smaller field of view combined with it's lesser magnification makes this eyepiece show within it's field of view nearly the same image as the Expanse. vs. Meade 25mm MA Meade's 25mm modified acromat showed itself to be more sensetive to hydrogen bandwiths than the Expanse, and indeed any other eyepiece in my collection, as it showed far more detail in the Orion Nebula. It's FOV is just about as narrow as the GTO Plossl. vs. Tasco 20mm MA Tasco's 20mm Eyepiece has a wide 58 degree field of view, not unlike Orion's Kellner and the Expanse. While it wasn't the best at anything compared to the Expanse, it does not have distorted seagulls in the edges of it's field of view. It's eye relief is about the same as the Expanse. So, there you have it. I think the Expanse is a nice eyepiece for showing the deep sky to friends and family and can be best enjoyed with nebulas and galaxies, but when used with star clusters the seagulls just get beyond annoying at least to me. What this eyepiece does offer is more of a feeling of looking through a spaceship's window... as if you are actually flying through space. If this Erfle gives that feeling, what would a Nagler do for me?
Xevious Nice post. The Orion expanse line is more for those requiring good eye relief, mostly for those with glasses. This line is notorioius for seagulls and other distortion problems near the edge. You shouldn't be buying this line for fast scopes, or the Erfles. For faster scopes, stick with the Super Plossls and stay away from the wide angle lens. And yes, the Naglers will never do you wrong.
Well, I do wear glasses a good part of the time. I don't have to wear them for Astronomy though, since my stigmatism is not sufficient to hamper my viewing in any way. I just refocus the telescope to suit my eyes... but I did notice that with my glasses on, the Expanse was comfortable to look through. Good point, Q.
I don't have to wear them for Astronomy though, since my stigmatism is not sufficient to hamper my viewing in any way. Faster scopes also present a higher degree of problems with stigmatism as opposed to slower scopes. It's very difficult to find eyepieces that will not only work with a faster scope, but will also not "magnify" the problems associated with stigmatism. My scope is very fast - f/4. And I have a difficult time finding the proper eyepieces that will work with this fast a scope. Once I do, the views are stunning. Collimation MUST be dead on, though. If you ever decide to go with a zoom lens in shorter focal length ranges, try out the Speers-Waler 5-8mm zoom, an excellent eyepiece for fast scopes and is not as expensive as the Nagler 3-6mm zoom, but works as well. I've heard it referred to as the "Poor-mans Nagler."
Collimation accuracy is indeed a must on faster scopes. It seems in my experience that slower focal scopes of around 700mm or more are more forgiving of the collimation not being as accurate. But when I went from my Spaceprobe 3" to my Tasco 114375, I ditched my collimation cap after a couple nights of observing for a Cheshire collimation tool. I think I'll look into that zoom you're telling me about.
