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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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i have the Omni 150r, f5. i have been using the following eps: 22pano, 17T4, 12T4, & 8mm Ethos. i have sold the 12 & 8, with plans on getting a 10mm Pentax XW... but then i saw a recient post where they were talking about the field curvature in my 150r. i commented that i see no curvature at all, in which 'russell23' commented that i must not see it due to the TV eps, but he does see curvature with the 10mm XW.
so now i am second guessing my choice of the XW. i understand it's a great ep, but if it won't work well in my scope, i am thinking i should just go for an Axiom.
i know the 10mm Ethos is out there, but i wanted to stay a little bit lower in the price range.
what are you thoughts on the XW at f5... not only for my current 150r, but the plan is for me to get an XX12, so i am wondering how it will work in that f5 also.
thanks for all your help,
david
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ausastronomer
scholastic sledgehammer
Reged: 06/30/03
Posts: 937
Loc: NSW Central Coast (Australia)
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I use it in 2 large F4.5 reflectors and an F5 reflector and it performs superbly in every respect. IMO it outperforms the 12mm Nagler T4, which I also own, in each of those scopes. Are you sure your friend doesn't just have a green tinge in his eyes?
Cheers,
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John Bambury
AS of NSW
AS of Hunter Valley
18"/F4.5 Obsession fully loaded with OMI optics
14"/F4.5 SDM fully loaded with Zambuto Optics
10"/F5 Newtonian with Argo Navis
Lots of Pentax XW's. 12mm & 17mm Nagler T4's, 31mm Nagler T5 & 13mm ETHOS. TV Paracorr and 1.8X TV Barlow and 2.5X TV Powermate
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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i'll let him answer that one, i sent him a PM to point to this thread!
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russell23
sage
Reged: 05/31/09
Posts: 427
Loc: Upstate NY
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Hi,
I had a few nights to try a 150mm f/5 Celestron XLT refractor with 14mm and 20mm XW's. The combination was not that great. There was significant field curvature and seagulls in the outer 25% of the field. The 14mm and 20mm XW's are sharp almost to the edge in my 120mm f/8.3. But with the 150mm f/5 their edge performance was no better than what a cheaper widefield EP is with my 120mm f/8.3.
However, I don't know that the same would be the case with a 10mm XW. From reading comments here I believe that one of the reasons the 10mm XW is considered one of the best in the line is that it doesn't have the same curvature as the 20mm and 14mm XW's. When I tried the 150mm f/5 I did not have the 10mm XW, so I never actually put that EP in the scope. So I would not recommend the 14mm or 20mm XW with the 150f/5 but the 10mm might be ok.
My impression with my 120mm f/8.3 scope is that the 10mm XW is better than the 14mm and 20mm. I think it has a flatter field and sharper to the edge - much more like what I've seen with a 27mm Pan and a 17mm T4 Nagler.
And no, I don't see green. I still have the XW's and the 27mm Pan and 17mmT4 Nagler were sold. The TV EP may have been sharpe at the edge, but I did not like the quality of the light as much. The 10mm and 20mm XW's are my favorite EP along with my 48mm Brandon.
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Tamiji Homma
Pooh-Bah
Reged: 02/24/07
Posts: 1092
Loc: California, USA
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This graph has been posted a few times on Eyepiece Forum before.
http://pentaxplus.jp/archives/tech/xo-xw/64.html
Even though it is in Japanese, you can see the graph. The DS/DM curve shows eyepiece field curvature characteristics. I think that telescope side of field curvature may cancel out eyepiece side to give you flat curvature free view as well as it may make it worse if both telescope and eyepiece has the same field curvature curve.
As you may notice, XW10, 7, 5, 3.5 has curved opposite direction to XW 14, 20, 30, 40...
Tammy
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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thanks for all the info.
i do have a follow up question, but i will start a new thread.
thanks,
david
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