Pentax 10.5mm XL Vs. 9mm Nagler T6

[bytor666]

How about somebody do a shootout between these two eyepieces?...I've been enjoying the Ultra Wide field of my Meade 4k 14mm UWA so much, that I just may have to pull the trigger on a 9mm Nag T6, and buy me one !!! :eyepop:

[janoskiss]

I don't know about the XLs but IMO the T6s don't come close to the <= 10mm XWs in terms of enjoyment, due to superior comfort and contrast of the XW. Giving up 12 degrees of a huge FOV is a small price to pay for the privilege and of little consequence IMO; 70 degrees is heaps. T6 are nice and compact though, much more pocketable and also make better travellers than XWs. Every EP is a set of compromises. btw: the T6 is very different to the 14mm 4k uwa. Try before you buy. ;)

Between the 9 and 10.5mm XL the biggest difference will be the focal length. What scope would they be for? What kind of observing?

[TomD]

Here's a Cloudy Nights review of the 9T6, Pentax 10XW, and Meade 5000 8.8 that might be helpful:

http://tinyurl.com/qlsqa

Tom

[ausastronomer]

Tom D,

Let me say I am a friend of Tom Trussocks, have corresponded with him over several years and respect his opinion greatly.

Having used all of those eyepieces I can't quite reach the same conclusions as Tom did. Obviously with such a comparison many of the differences relate to personal preferences.

Physically the Pentax is a lot bigger with much longer eye-relief and a larger eye-lens providing a lot more comfort and a more submersive view despite the narrower AFOV. Optically, the differences between the 10mm Pentax XW and the 9mm Nagler T6 are not great but detectable to my eye, after allowing for the difference in focal length. IMO the 10mm Pentax XW has superior sharpness, contrast and light throughput. It definately goes deeper in resolving stars in globular clusters on the verge of visibility. It also offers a cooler tone (whiter) on the moon and planetary features. The 9mm Nagler T6 also shows a little distortion towards the EOF which is non existent in the Pentax XW. If you put a target like Jupiter at the EOF in the Nagler it goes "egg shaped", it stays perfectly round in the Pentax. PS: Don't try this on Saturn because it is egg shaped :)

In favour of the 9mm Nagler is the fact that it has a slightly wider AFOV, which to me is not a consideration as I don't use that extra FOV anyway and the fact that it is much smaller and lighter making it suitable for use in a binoviewer.

In conclusion I would say that if you don't own a binoviewer and don't need that little bit extra AFOV, you take the 10mm Pentax XW every time. Keeping in mind of course that the 9mm Nagler T6 is also an outstanding eyepiece and if the Pentax was not born, I could live happily with the Nagler forever. If you want the best the 10mm Pentax XW is it IMO.

Also remember that in Australia the 10mm Pentax XW is almost $AUS 50 cheaper than the 9mm Nagler T6.

CS-John B

[TomD]

Hi John,

I posted the link to Tom T.'s review only because I thought it might be helpful to the original poster and for no other purpose. Although I own a 9T6, I've never looked through any of the other ep's identified in Tom's review nor elsewhere in this thread; therefore, I cannot comment on the performance of these other ep's nor how they may compare to each other or to the 9T6. I do agree with your suggestion that ep selection is personal and subjective. For example, while Jupiter appears to you to be egg-shaped in the 9T6, it has always looked round to me....everybody's experience at the eyepiece is a going to be little different.

Tom

[janoskiss]

Well, that's hardly a subjective thing; whether Jupiter is egg or disk shaped. I think its a matter of magnification. You need to use the EP in a long focal length scope where it produces high magnification to see the "egg" shaped Jupiter.

[TomD]

You are correct...it was a poor example of subjectivity. In any event, I have a (fairly) short fl scope (f/6.2) and, as you said, that is probably why Jupiter looks round to me.

Tom

[bytor666]

I think that John B. was referring to the image being egg shaped at the edge of the field in the T6 naglers. The Pentax still shows a roundish shape in a Pentax 10mm and up near the edge of the field as well as anywhere else.
Some of the pentax XW's are incredibly , highly corrected eyepieces..and I WON'T be in eyepiece nirvana until I purchase a 10mm or 7mm Pentax XW again !!!! :party2:

[CoombellKid]

I'm not say'n anything :whistle:

regards,CS sunny days

Rob

PS: Put it down to post count building

[davidpretorius]

geez, pentax wins again.....i now have a 4mm TMB, 5mm Vixen LV and basically crap after that

10mm pentax XW sounds the goods!

[CoombellKid]

Didn't they star test the Hubble with a 10mm XW last time they were up
there fixing it :P :lol: :ashamed:

regards,CS sunny days

Rob

[Don Pensack]

It's always a compromise, when designing an eyepiece. If you want tightly focused, pinpoint stars at the edge of an 82 degree field of view, you will tolerate pincushion distortion (aka angular magnification distortion) to eliminate astigmatism at the field edge.
You can narrow the field of view and design out some of the pincushion (like the Pentax XW), or you can allow for more field curvature (like the Pentax XW), but it's always a compromise.
How many people view Jupiter as it leaves the field of view? If you do, then the Pentax is for you. The Pentax makes a better daytime eyepiece (in spotting scopes, rectilinear distortion is a no-no), and it is more "orthoscopic" in its control of aberrations). But it isn't an 82 degree field eyepiece, and it isn't perfectly sharp at the edge either (I've used a lot of them in my scope, and though they're VERY nice eyepieces, they aren't perfect either).
And, like any non-scaled eyepiece line, they vary in aberrational characteristics with focal length (just like the Nagler T6's).

So it depends what you want. Planetary, daytime, sky-scanning, or long eye relief, the XWs will probably be preferred. Widest field, sharpness of stars at the edge, and ease of use without glasses (including balancing issues), probably the T6's.
It's like evaluating fine cabernets. Some people prefer one, some the other.
They're both QUITE good. Just different.
Don

[davidpretorius]

thanks don

[janoskiss]

I don't know if it's just me, because I don't hear other people complaining, but the XWs along with all other super-to-ultra-wides I've tried have way too much chromatic aberration to be useful right-to-the-edge as planetary EPs. e.g., there is strong red/green fringing on Jupiter. It starts appearing at half-way between centre and edge, where it can still be helped by adjusting eye placement. But a bit farther out, certainly outside the central 50-degrees, there is too much CA for pleasing planetary viewing. Understandably it's most apparent in my largest scope, the 12", but also there in the smaller ones.

[Don Pensack]

I've heard this from others and I do notice it at the edge in most ultrawidefields, but I find it's related to the position of the eye and head in relation to the exit pupil. I think most of the CA can be corrected with eye placement out to fairly near the edge. If you hold your eye in the wrong spot, it can even be seen fairly close to the center.
It may be (I'm speculating here) related to that characteristic called "spherical aberration of the exit pupil" which, though controlled in most ultrawides, is not totally eliminated.
Whatever the case, since it can be tempered by eye placement, it is not usually considered a big deal.
But if you let the planet drift to the edge, a narrower field eyepiece may be better.
But which one?
Aye, there's the rub.

[janoskiss]

I know what you mean about eye placement Don. I find that nearing the edge of field, eye placement needs to be fairly "extreme" to minimise CA in the XWs, i.e. quite a long way off-axis and closer to the lens (the eyecup needs to be readjusted compared with ideal position for on-axis viewing). Don't get me wrong, I'm not knocking the XW, in fact it's my preferred choice for all types of viewing, but newcomers to the hobby need to understand that no eyepiece is perfect, not even the best ones.

It may surprise some that I find the 13mm Stratus in my 2" barlow better with regard to off-axis CA than the 7mm XW. The barlowed Stratus has CA under control over most of its FOV (all but the last few degrees) with much gentler purple-green fringing that does not need much shift in eye placement to minimise. This is with a very long and very good barlow though where the 13mm sees a much slower light cone (f/11) compared with the 7mm w/o barlow (f/5). A fairer comparison would be with the 14mm XW in the same barlow. But I don't have the 14mm XW anymore and when I did I never compared.