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Equipment Discussions >> Eyepieces

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t.r.
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Ethos vs. Pentax XW? new
      #4129062 - 10/20/10 09:54 AM

Based on the center of view (call it 70 degrees if you wish) which of these two eyepieces is better and why? You cannot use the 100 degree advantage of the Ethos or price in your assessment. Transmission, color, clarity, sharpness, details rendered, ease of use(ergonomics)etc. is the criteria on which to judge. If you cannot objectively discount the extra fov of the Ethos (Majesty Factor)/price, then please withhold comment. This can be considered an apples to oranges comparison by some,but I have set limits to narrow and focus (no pun intended) the conversation.

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sixela
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129113 - 10/20/10 10:16 AM

Pentax XW wins, but the difference is extremely small (much smaller than the Nagler T6 vs. Pentax XW difference). It's so small that I tend to use my 21mm Ethos plus Baader VIP screw-on barlow more often these days than my Pentax 10mm XW (saves me a trip to the eyepiece case).

I think if you are satisfied with 70° AFOV and have money to burn, then you shouldn't be looking at an Ethos if you want an alternative to the Pentax, but at the Nikon NAV SW.


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Richard McC
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Re: Ethos vs. Pentax XW? [Re: sixela]
      #4129134 - 10/20/10 10:26 AM

Does the extra 5mm of eye relief (XW 20mm v Ethos 15mm) mean anything to you? I find it makes observing more comfortable for me but everybody is different.

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FLYcrash
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Re: Ethos vs. Pentax XW? new [Re: Richard McC]
      #4129152 - 10/20/10 10:34 AM

Quote:

Does the extra 5mm of eye relief (XW 20mm v Ethos 15mm) mean anything to you? I find it makes observing more comfortable for me but everybody is different.




When I wear glasses, I totally agree. 15mm is just little enough to feel a bit cramped with glasses on at the eyepiece. OTOH, when I have glasses off, the 12mm of the Nagler T6 series feels just right.


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Jeff Morgan
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129159 - 10/20/10 10:36 AM Attachment (69 downloads)

I just bought the 40 XW in the hopes of replacing the 31 Nagler and 41 Panoptic. It has much better mechanicals than the Tele Vue product (helical eyecup, bevelled barrel, and not-quite-as-obnoxius "safety" undercut). Tele Vue would do well to swallow their pride and copy the first two features, and drop the hated undercut entirely. But the biggest feature for me was the weight: about 2/3 that of the Tele Vue behemoths.

Since buying the eyepiece I have had a chance to test it against the Tele Vues in a TMBss 80 mm f/6 APO and a 12.5" f/6 Newtonian. I wanted to say "exhaustively" tested, but I can not say that, because I could not get past one issue with the Pentax - stars that are sharply focused in the center of field become markedly de-focused about 2/3 of the distance to the edge. (Both the mentioned Tele Vues stayed very sharp to 85-90%, and reasonably sharp to the field edge.) Viewing the large star clusters in the WX was not a pleasant experience.

Based on what I have heard about the Pentax XW, part of me thinks that the person who assembled this eyepiece did it incorrectly. What I was seeing was totally at odds with the Pentax buzz. But I had little time to find out as I was nearing the end of my 30 day return rights with our host Astronomics. I sent the XW back last week.

Grudgingly, Tele Vue is still wide-field king.

But if center field sharpness is really what you're after, get some Brandons. They club my Tele Vues like a baby seal.

Edited by Jeff Morgan (10/20/10 10:37 AM)


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FLYcrash
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Re: Ethos vs. Pentax XW? new [Re: Jeff Morgan]
      #4129197 - 10/20/10 10:52 AM

Hmmm...it's good to know that the 40 XW shows field curvature (at least to some eyes) even at f/6.

I can vouch for the 7 and 10 XW, though. I've put mine into f/6 and even f/4 scopes and have been nothing but delighted. OTOH, I was so absorbed in what I was observing at the time that I hardly paused to check the edge-of-field performance...but that's the way I like my observing to go. YMMV.

Edited by FLYcrash (10/20/10 10:53 AM)


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sixela
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Re: Ethos vs. Pentax XW? new [Re: Richard McC]
      #4129223 - 10/20/10 11:05 AM

Quote:

Does the extra 5mm of eye relief (XW 20mm v Ethos 15mm) mean anything to you?




To me, no. In fact, were it not for the excellent eyeguard design on the XW, I'd find its long eye relief rather annoying. The Ethe are Just Right for me.


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sixela
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Re: Ethos vs. Pentax XW? new [Re: Jeff Morgan]
      #4129237 - 10/20/10 11:09 AM

Quote:

stars that are sharply focused in the center of field become markedly de-focused about 2/3 of the distance to the edge.




The field curvature is very different from that in Pans (except in the focal lengths from 10mm down). But whether that's objectionable depends on a lot of things: the field curvature of your scope and its sign, how well your eyes accommodate for focus, how you focus (on some scope/eyepieces in order to accommodate well for the entire field you need to focus at the edge and accommodate for the centre or vice-versa, and the other doesn't work),...

Short Newts seem to bring out the worst of this.


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russell23
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Re: Ethos vs. Pentax XW? new [Re: FLYcrash]
      #4129375 - 10/20/10 11:58 AM

Quote:

Hmmm...it's good to know that the 40 XW shows field curvature (at least to some eyes) even at f/6.

I can vouch for the 7 and 10 XW, though. I've put mine into f/6 and even f/4 scopes and have been nothing but delighted. OTOH, I was so absorbed in what I was observing at the time that I hardly paused to check the edge-of-field performance...but that's the way I like my observing to go. YMMV.




The 10mm and shorter XW's are different from the longer FL XW's. The 10mm and 7mm XW are sharp to the edge in a fast system.

Dave


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russell23
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Re: Ethos vs. Pentax XW? new [Re: russell23]
      #4129390 - 10/20/10 12:04 PM

Ditto's on the Brandons. Get a 24mm Brandon which has ~20mm of eye relief and a few good barlows and you're set.

My 24mm Brandon barlowed has beaten every wide field I've looked through for detecting faint stars.

The 26mm Celestron Vixen silvertop plossl comes pretty close to the Brandon.

Dave


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BadClams
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Re: Ethos vs. Pentax XW? new [Re: Jeff Morgan]
      #4129414 - 10/20/10 12:12 PM

Quote:

They club my Tele Vues like a baby seal.




Now that's just plain funny!


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Scott99
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Re: Ethos vs. Pentax XW? new [Re: Jeff Morgan]
      #4129511 - 10/20/10 12:48 PM

>>>Based on what I have heard about the Pentax XW, part of me thinks that the person who assembled this eyepiece did it incorrectly. What I was seeing was totally at odds with the Pentax buzz.

Nothing wrong with it - the 40mm XW is definitely not sharp to the edge at f/6. 30mm XW is a much better match for f/6 if you're after edge sharpness.

The 30mm, 10, 7, 5, and 3.5mm XW's are the ones that work great with any f/ratio. The 40mm, 20mm and 14mm are great ep's but IMO better at f/8 or f/10+ if you want edge sharpness.


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t.r.
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Re: Ethos vs. Pentax XW? new [Re: Scott99]
      #4129815 - 10/20/10 02:57 PM

Does anyone know the design critical F/ratio for the Pentax?

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Tamiji Homma
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129842 - 10/20/10 03:08 PM

Quote:

Does anyone know the design critical F/ratio for the Pentax?




I think XW is designed for f/4 or slower scope. It is in Japanese but
http://pentaxplus.jp/archives/tech/xo-xw/61.html

Tammy


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RAKing
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129850 - 10/20/10 03:12 PM

The Pentax has very nice ergonomics. I love the twist up eyecup and the 20mm eye relief - and I don't even wear glasses. It's just a very comfortable eyepiece to use.

But if you have a scope that can really benefit from the wider field, the Ethos is sharp all the way across. I'm sorry this steps over the boundary of your question, but it's the main reason I finally sold my last Pentax a couple weeks ago. It was just stuck in the case and not getting any use.

Cheers,

Ron


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t.r.
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Re: Ethos vs. Pentax XW? new [Re: RAKing]
      #4129873 - 10/20/10 03:20 PM

I understand Ron. I see in your sig that you have an apo as well as an sct. How do you feel the Ethos performs in the sct vs. the XW? The curvature in the sct design should allow the XW to perform better, all the way to its edge vs. the Ethos...

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sixela
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129903 - 10/20/10 03:35 PM

Quote:

Does anyone know the design critical F/ratio for the Pentax?




It works well on an f/4 scope with Paracorr (better than Plössls and orthos). It's just that the 40mm Pentax has more field curvature and that it shows wide fields and thus also the most scope field curvature of the series. By the way, if I'm careful about which stars I use to focus (and to keep my eye focused at infinity while I focus) I can still manage to focus in such a way that my eye accommodates all of the field curvature in my 400mm scope, though not in my Starblast with 2" focuser (which has a lot more field curvature).


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RAKing
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Re: Ethos vs. Pentax XW? new [Re: t.r.]
      #4129964 - 10/20/10 04:00 PM

Quote:

I understand Ron. I see in your sig that you have an apo as well as an sct. How do you feel the Ethos performs in the sct vs. the XW? The curvature in the sct design should allow the XW to perform better, all the way to its edge vs. the Ethos...




I was not able to use the Ethos in the older, "regular" SCT. Everyone's tolerance to field curvature is different and mine must be very low. On-axis, everything was fine in all of these eyepieces, but the view quickly deteriorated as I moved off-axis and this is the reason I had a good selection of Pentax XL, XW, and Televue Panoptics.

The newer generation SCT (Edge, ARC/ACF) have much better edge correction with flatter fields and I can use the Ethos in these. FWIW - I had an 8 inch Edge, but let it go in favor of the bigger aperture ARC. Both of my scopes now work equally well with the Ethos and this finally tipped the scales in their favor.

Again, I'm sorry I stepped over the line of your FOV boundary, but after I opened my peripheral vision with the Ethos, there was no going back. YMMV of course.

Cheers,

Ron


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johnnyha
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Re: Ethos vs. Pentax XW? new [Re: RAKing]
      #4130889 - 10/20/10 10:23 PM

I had the same experience as some others, I got the 40mm XW and returned it, it just didn't compare to the 31T5 which is sharp to the edge in my refractors and in my dob with a Paracorr. For me Ethos wins against Pentax down to 13mm Ethos, and then Pentax 10 ,7, 5 and 3.5 beats Ethos 10, 8, 6 and 3.7. I've had all these eyepieces more than once except the 10mm Ethos and 3.7 Ethos.

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gnowellsct
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Re: Ethos vs. Pentax XW? [Re: FLYcrash]
      #4135320 - 10/22/10 08:41 PM

Quote:

Hmmm...it's good to know that the 40 XW shows field curvature (at least to some eyes) even at f/6.





I use the 40xw in an f/6 10" Newt (and the 30 xw too) and am quite pleased with it. I wonder if the negative appraisal is an indication of eyepiece accommodation.

In my f/8 FS128 I spent a good deal of time comparing the Pan 41 adn the XW40 and found no significant performance difference between the two. There is of course a price and weight difference.

Greg N


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