Pentax XW 10mm vs ES 12mm 92°

[vagk]

Has anyone compared Pentax XW 10mm vs ES 12mm 92° in fast scope ? Which one do you recommend (sharpness, edge correction etc) ?

 

 

[John]

I've owned both but I never actually compared them. Probably similar in terms of sharpness and edge correction. Massively different in all physical and ergonomic respects though.

I found the eye relief of the ES 12 / 92 just too long for my comfort. Even with the eye cup fully extended I had to "hover" my eye well above the eyepiece top to get the right position (I don't wear glasses when observing) and, speaking personally, I don't find this a relaxing way to observe. A also have the Ethos 13mm which I preferred over the ES 12 / 92 in practically all respects.

I let the ES 12 / 92 go to a new home quite quickly but held onto the ES 17 / 92 for longer because the eye positioning was easier to hold with that one. I still have the Pentax XW 10mm though.

I would have thought that the Baader Morpheus 9mm or 12.5mm would be a closer comparison to the Pentax XW 10mm ?

 

[vagk]

What I have read about 12mm 92° is that you observe whole 92° AFOV at a glance instead of ethos or es 100° which you must move your head and eye to capture whole field of view. This must be spectacular.

Isn't worth the sacrifice of ergonomics and weight for 32 degrees extra AFOV with the same eye relief ?

[John]

1 hour ago, vagk said:

What I have read about 12mm 92° is that you observe whole 92° AFOV at a glance instead of ethos or es 100° which you must move your head and eye to capture whole field of view. This must be spectacular.

Isn't worth the sacrifice of ergonomics and weight for 32 degrees extra AFOV with the same eye relief ?

Personally I don't need to move my head to see the full field of the Ethos but I know that some folks do. Seeing the whole of a 92 degree eyepiece with nearly 20mm of eye relief is going to be a little easier than for a 100 degree eyepiece with 15mm of eye relief, especially if you wear glasses.

Optically the ES 92 degree eyepieces are excellent - the best that I've used from ES by some way. I just did not find the eye placement suitable for me.

Not sure how to answer the final question - I enjoy both hyper-wide eyepieces and ones with around 70 degrees as well. I usually use the 70 degree ones in my refractors and the 100 degree ones in my 12 inch dobsonian.

Edited November 30, 2021 by John

[Don Pensack]

9 hours ago, vagk said:

What I have read about 12mm 92° is that you observe whole 92° AFOV at a glance instead of ethos or es 100° which you must move your head and eye to capture whole field of view. This must be spectacular.

Isn't worth the sacrifice of ergonomics and weight for 32 degrees extra AFOV with the same eye relief ?

Be careful.

Human vision can see well beyond 100° with peripheral vision.

You can see the whole field at a glance in a 120° eyepiece with peripheral vision, but NOT direct vision.

Foveal vision--the center of the retina we use to look directly at something--cannot be redirected to the side of a field larger than about 68-70° without rolling the head over and looking through the eyepiece at an angle

(as you would do with a porthole to see farther at the edge).  Much of the time, whether you are even aware of doing so is simply related to your experience with the field size.

I have used 100° eyepieces since 2007, so I found the 92s easy to use and about the same as the Ethos eyepieces I was familiar with.

 

But if you want to look directly at the edge (and in practice you really don't), you have to roll your head over.  If you try to simply avert your eye to look at the edge, you would move your pupil away from the exit pupil of the eyepiece.

To look with direct vision at the edge means you are looking through the eyepiece at a 46° angle.  Try doing that without rolling your head over and you'll see your pupil moves several millimeters to the side to do so.

And that doesn't work with eyepieces.

 

So the people who maintain you can take in the whole field at a glance with direct vision are blowing smoke.  It's anatomically impossible.

Peripheral vision is easy.

 

Edited December 1, 2021 by Don Pensack

[Louis D]

The problem I've had with some lower cost 90+ degree eyepieces is that the eye relief is so short and my eyes are so deep set in my sockets that I simply cannot push in close enough to see the entire field at once because the top of the eyepiece is typically too broad to fit within my eye socket.  I've even seen this with vintage ~80 degree AFOV binoculars that had rigid eye cups which were about as deep as the usable eye relief.  Even with my eyeglasses off I couldn't take in the entire AFOV.

Other UWA eyepieces have too much SAEP to be able to take in the entire AFOV at once, such as the Meade MWA 26mm, and to a lesser extent, the 12mm and 17mm Nagler T4s.  I have to pull back a bit to get a usable exit pupil with these eyepieces, losing a bit of AFOV in the process.

I haven't had either issue with the 12mm ES-92 thanks to its fairly well controlled SAEP (not perfect, but not terrible) and long usable eye relief.

[John]

The ES 92 eyepieces have proved very popular for those who wear glasses when observing because they are practically the only hyper-wide eyepieces that give eye relief that is sufficient to allow them to access the full AFoV although, as Don Pensack says, there will be some movement of the eyeball, and maybe, albeit unconsciously, the head, required to do this.

For me as a non-glasses wearer, I found the eye relief of the 12mm too long and therefore the eye positioning awkward and the 17mm almost so but I did manage to deal with that one better. They are both very large and heavy eyepieces with very high optical performance even in scopes down to around F/5.

 

 

[vagk]

On 30/11/2021 at 16:21, John said:

I've owned both but I never actually compared them. Probably similar in terms of sharpness and edge correction. Massively different in all physical and ergonomic respects though.

I found the eye relief of the ES 12 / 92 just too long for my comfort. Even with the eye cup fully extended I had to "hover" my eye well above the eyepiece top to get the right position (I don't wear glasses when observing) and, speaking personally, I don't find this a relaxing way to observe. A also have the Ethos 13mm which I preferred over the ES 12 / 92 in practically all respects.

I let the ES 12 / 92 go to a new home quite quickly but held onto the ES 17 / 92 for longer because the eye positioning was easier to hold with that one. I still have the Pentax XW 10mm though.

I would have thought that the Baader Morpheus 9mm or 12.5mm would be a closer comparison to the Pentax XW 10mm ?

 

So, as you had owned both, do you believe Pentax XW 10mm is a better option for f/5 Dobsonian than ES 12mm 92° ? 

Edited December 1, 2021 by vagk

[John]

1 hour ago, vagk said:

So, as you had owned both, do you believe Pentax XW 10mm is a better option for f/5 Dobsonian than ES 12mm 92° ? 

It depends what you want. If you want a hyper-wide field of view then the ES 92 is the one. If you want a lighter, smaller eyepiece and are happy with a 70 degree field of view, the Pentax XW is a very nice eyepiece. There is quite a cost difference between the two as well which might be important as well - in the UK the ES 12mm 92 costs £160 more than the Pentax XW 10mm which is quite a significant amount.

Optically they will both perform well in an F/5 dobsonian. The ES will need some additional counterbalancing because of it's weight and it is a 2 inch eyepiece of course so it will need 2 inch filters if you use those.

Sorry that I can't offer a conclusive answer but they are very different eyepieces in many ways.

Edited December 1, 2021 by John

[Don Pensack]

Something in-between: 12.5mm Baader Morpheus.

It has a (measured) 78° field and plenty of eye relief for glasses.

It is noticeably wider than the XW and the Delos and has excellent sharpness and contrast.

[Louis D]

If you're in the US, the 10mm Pentax XW goes for $269 right now while the 12mm ES-92 goes for $799, a huge $530 difference.  In fact, you could almost buy three 1.25" XWs for the price of one ES-92 (you'd need $8 extra).

Another possibility would be the APM Hi-FW 12.5mm.  You would still have great sharpness while remaining in a 1.25" barrel.  The price is $375 in the US and €247.90 in Europe, both excluding taxes.  This puts it in the XW price range.