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Pentax XW "newbie"


Timebandit

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44 minutes ago, Dude_with_the_tube said:

....Sometimes,reading forum reviews of eye pieces are not really beneficial as folks tend to exaggerate something what isnt really necessary :)

 

I think this does happen. What is a "big deal" to one observer might be of no consequence at all to another. I also think that what might have been a throwaway comment gets picked up and repeated often on forums so assumes an significance way beyond the originally intended one.

When I was reporting on eyepieces for the forum I often re-wrote my reviews several times to try and ensure that they were balanced and that I was not inadvertantly putting too much or too little emphasis on something. It's not easy ! :rolleyes2:

I'll look forward to reading your reports on the eyepieces :smiley:

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2 hours ago, Dude_with_the_tube said:

Field curvature will become obvious in dobs,but in refractors you will not see it.

In relation to XW eyepieces?  Short refractors have a lot more field curvature than just about any dob.  My AT-72ED's FC is so bad, I bought a zero power field flattener that I could screw onto the front of my 2" diagonal.  My 8" dob shows some FC, but coma completely overwhelms it.  A coma corrector that also helps to flatten the field like the Paracorr or GSO models help correct both at the same time.

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4 hours ago, Louis D said:

I have the 14mm Morpheus and compared it to my XLs/XWs/Delos/NT4s/ES-92.  It is as sharp in the center 80% as the best out there.  The last 5% to 10% clearly show a little field curvature and a little bit of astigmatism when a star is defocused.  In focus, it's not noticeable.  Only the NT4s also show a little defocused astigmatism.  Overall, the Morpheus is a very good deal, especially given its 76 degree field and 19mm of usable eye relief.  It's also noticeably lighter than the comparable Pentax and Delos offerings.

I had a similar experience with a Baader Morpheus 14mm. In my F/6 and F/10 scopes astigmatism wasn't a huge problem, but field curvature was. I personally do not like field curvature much, which is why i got the Delos 14mm instead (a new one was going cheap). Someone else on SGL is apparently very happy with the Morpheus now. The 14mm Delos cannot easily be made parfocal with the XWs, but I can live with that, because the Nagler 12t4 sits in between anyway.

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1 minute ago, michael.h.f.wilkinson said:

The 14mm Delos cannot easily be made parfocal with the XWs, but I can live with that, because the Nagler 12t4 sits in between anyway.

You'd have to buy a 2" to 1.25" ultra low profile adapter to actually sink the Delos down enough to make it parfocal.  I added a 20mm extension ring to the bottom of my 12mm T4 and then added enough 4mm thick rubber O-rings to bring it to near parfocality with most of my other eyepieces.

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14 minutes ago, Louis D said:

You'd have to buy a 2" to 1.25" ultra low profile adapter to actually sink the Delos down enough to make it parfocal.  I added a 20mm extension ring to the bottom of my 12mm T4 and then added enough 4mm thick rubber O-rings to bring it to near parfocality with most of my other eyepieces.

That would work (but essentially that would require a 2" adapter for each EP). However, I only really use the EPs from 10 mm focal length and lower for planetary work, where quick changes of magnification are useful as conditions change, so you do not want to refocus. The Delos 14mm and Nagler 12T4 are great for small galaxies and planetary nebulae, but those rarely require the kind of quick changes I like to do in planetary work

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I bought the 17.3mm Delos because it was closer to the focus position of the XW's than most TV eyepieces. I believe the 14mm Delos shares the same focal plane position as the 17.3mm but the other Delos are the same as many other TV eyepieces in their par-focal group "B".

The 17.3mm Delos requires a little more inward focus than the XW's but not a lot.

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1 hour ago, John said:

I bought the 17.3mm Delos because it was closer to the focus position of the XW's than most TV eyepieces. I believe the 14mm Delos shares the same focal plane position as the 17.3mm but the other Delos are the same as many other TV eyepieces in their par-focal group "B".

The 17.3mm Delos requires a little more inward focus than the XW's but not a lot.

The XLs, XWs, AT AF70s, 14mm Morpheus in 1.25" mode, Orion/GSO plossls, and most of my ES eyepieces (I don't have them all, so I can't speak for all of them) focus at or very close to the shoulder.  The Delos 12mm and below focus 1/4" below the shoulder, requiring the focuser to be racked outward that amount from the shoulder-focusing eyepieces.  The 14mm and 17.3mm Delos both focus 1/4" above the shoulder, thus requiring inward focus as you state.  While it's quite easy to put O-rings on the TV B parfocal group (12mm and below Delos and many others), those focusing below the shoulder are a pain to bring to parfocality because you'd have to put O-rings on everything else that focuses at the shoulder just to accomodate them.  That, or use an ultra-low profile 2" to 1.25" adaptera on the 14mm/17.3mm Delos that submerge the eyepiece below the shoulder.  I have the 10mm Delos and find that 0.25" of focus out-racking to be mildly annoying.  It's not enough to warrant parfocalization, yet.

As far as I can tell, the 17mm Nagler T4 is the only TV eyepiece that focuses at the shoulder like the majority of non-TV eyepieces.  By contrast, the 12mm NT4 focuses 3/4" below the shoulder, requiring lots of racking out of the focuser.  It was so annoying, I put a 2" diameter 20mm barrel extension on the bottom of the 2" skirt and then added 5 4mm thick 50mm inner diameter O-rings to the skirt up against the shoulder to bring it to near parfocality.  A parfocalizing ring wouldn't work because it needed to be tightened on one of the undercut tapers (the lower one I believe) to be positioned correctly.  That, and I didn't want to mar the skirt with the pointy set (grub) screw.  The O-rings are tight enough to fit snugly into the undercut securely, so that's not an issue.

I have no idea why TV decided not to position the focal plane at the shoulder for just about all of their eyepieces.  I have yet to find another line of eyepieces so dead-set against focusing at the shoulder.

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Try the Ethos range - they are all over the place !

Still brilliant eyepieces though and worth the effort.

I have faith that TV do what they do because thats the way it needs to be done to get the best from the optical design. Maybe I'll be proved wrong in this someday though :dontknow:

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2 hours ago, Pig said:

You finally have your hands on one then Simon :hello:Congratulations.

 

Hi Shaun , I have finally took the plunge. I still think you should of let me have your final Pentax, as it must be lonely in the company of the Ethos?. 

But I finally gave into temptation and decided the empty place in the case needed to be completed with the 5XW. Just great eyepieces Shaun, but you know that already as you started me down the enlightened path of the Pentax XW ☺

 

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