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Old 29-04-2012, 12:06 AM
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mental4astro (Alexander)
kids+wife+scopes=happyman

mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,979
Dear, oh Dear!

I've just come in from a very interesting couple of hours with my 17.5" f/4.5 dob. Ol' Wavytone was very generous today (Saturday), and lent me a couple of his most prized pocessions, two of his LVW's, the 13mm and the 8mm. I was hoping to be able to compare them to my problematic 13mm Hyperion, and gererally be prepared to have my socks blown off. What happened in the end I did not expect.

What spurred this lending of Wavy's LVW's was both THIS thread, and my poor experience of my recently acquired used 13mm Hyperion. This thread without saying is a gem. My Hyperion however was a disappointment. Using the same 17.5" scope, the stars in the Hyperion refused to come to a nice, crisp, sharp focus. Sure, if you concentrated on a single star the image became pin-point, but it didn't hold. There was some sort of mismatch happening between the optics and my eyes. The field curvature was appauling too! I have never seen such a "fishbowl" effect in any eyepiece. My observing companion that night, erick here on IIS, also saw this. Major disappointment.

When Wavy' dropped of the eyepieces, we examined both 13mms. We noticed that the field lens of the LVW was convex, but that of the Hyperion was concave. Odd since this field lens arrangement is supposed to be a barlow, and should be the same if the Hyperion is a copy of the LVW.

I should note here before continuing that the bottom 1.25" section of all Hyperion EPs unwinds from the two inch barrel fitting. This is part of the modular construction of these EPs that allows for different extension rings to be used, there by allowing one EP to become of two, three or maybe even four different focal lengths. The 24mm (of which I also have one) the 1.25" barrel has no lens in it, therefore is an empty shell with a thread for filters.

My test DSO was Eta Carina. The Hyperion was terrible, as the first time I used it. The LVW was in a league of its own here. The added 3 degrees FOV of the Hyperion only provided a slightly larger AFOV, but the field stop was soft, while that in the LVW was a nice sharp edge.

Then, a fit of maddness overtook me. I swapped the 1.25" barlowed barrel of the 13mm Hyperion for the empty barrel of the 24mm Hyperion, AND to it added the barlow lens element of my $30 1.25" GSO 2X barlow. Man-oh-man! What a difference! All of a sudden, the "modified" 13mm Hyperion had found its Mojo. The bugger focused as sharp as the LVW. The field curvature was gone. The field stop was still soft, but not really of consequence, as the extra 3deg of FOV remained the same.

HOWEVER, the real difference came when I nit-picked the faint stars around in Eta Carina. Switching between modified Hyperion and LVW constantly, I was actually seeing more stars in the modded Hyperion that the LVW. A faint cluster of stars immediately beside the star Eta Carina in the LVW required averted vision to JUST see them. With the modified Hyperion, I could see these same stars directly! and them even more stars with averted vision!

Holy Crap!

Contrast wise I could not really notice any difference. Probably due to the heavy light pollution I was viewing from. But, I cannot get away from the fact that I could see more in the modified Hyperion that I could in the LVW! I was considering rolling my 13mm under a fast moving truck earlier today. I'm keeping her now! "Frankenstiened" and all.

I then moved onto the 8mm LVW. As Eta Carina had now moved into a more light polluted section of my sky, I the test DSO became the open cluster in Scorpio NGC 6231. My comparison eyepiece was my $50 9mm TMB Planetary Type II. This TMB eyepiece only has a 60degree FOV, compared to the 65degrees of the LVW. I was in for another surprise.

This modest TMB eyepiece showed better contrast than the LVW. At this magnification, approx. 200X, the background sky in the TMB was a little blacker than in the LVW. Really small, but noticeable. The same thing also happened with this TMB, where I was able to see more stars through it than in the LVW. It also focused sharper. While the FOV of the TMB was smaller, the AFOV was larger than that of the LVW, maybe 4" or 5" (minutes of arc that is).

All of a sudden, I am at a bit of a loss at what has happened tonight! I had expected to have my eyeballs assulted by the quality of the LVW, but they have been out done by a modified Hyperion, and a $50 TMB. I am guessing that the edge that the TMB also has is the bugger all glass it contains compared to the LVW. Still, I would not have imagined such a significant difference.

I have now reconsidered my eyepiece collection from what I had been thinking only upto four hours ago. Sorry all of you LVW affeccionados - you have lost me. Coming to this shoot-out tonight, I had been gunning for the LVW's. In the end I've got new champions, and they were in my eyepiece collection all this time!

Mental.
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