PENTAX XW16.5 and PENTAX XW23

[wavelandscott (Scott)]

Interested in everyone's thoughts on these new eyepieces...

https://pentaxrumors.com/2022/11/10/...al-telescopes/

I will be in Japan in December and with the exchange rate (Yen and $USD) what it is, I may need to do some thinking about my needs.

[-Ephemeral- (Alex)]

I'm quite surprised by the weight figures. Both of the new eyepieces will weigh more than my 40XW!

I felt weight was a strength of Pentax but I guess that might change with the new releases.

[AG Hybrid (Adrian)]

Interesting to know if they have the same field curvature curse the 14mm and upwards are afflicted with.

[Stonius (Markus)]

Originally Posted by AG Hybrid

Interesting to know if they have the same field curvature curse the 14mm and upwards are afflicted with.

I'm surprised to hear you say that. I haven't noticed this in any of my scopes, and I notice some of gear is broadly comparable. Sure the XW's have some field curvature, as all eyepieces do, but it's been below the threshold of detection for me. I'm much more bothered by chromatic distortion, atmospheric refraction, or even the barrel distortion in my TV Pan24 (but that's another story - just don't pan with the Pan!).



Can I ask if its worse with certain scopes? Supposedly they're designed with refractors in mind, so I wonder if it becomes more of an issue on very fast dobs (mine is f5).



It's strange though as the XW40-14mm supposedly have positive curvature, and XW10 and above have negative curvature, so you would expect whatever field curvature issues you had to resolve either in the 14 or the 10mm as they have opposite curvature from each other.


Just strange how we can have such different experiences with the same EPs.



Cheers,
Markus

[ausastronomer (John Bambury)]

Originally Posted by Stonius

I'm surprised to hear you say that. I haven't noticed this in any of my scopes, and I notice some of gear is broadly comparable. Sure the XW's have some field curvature, as all eyepieces do, but it's been below the threshold of detection for me. I'm much more bothered by chromatic distortion, atmospheric refraction, or even the barrel distortion in my TV Pan24 (but that's another story - just don't pan with the Pan!).



Can I ask if its worse with certain scopes? Supposedly they're designed with refractors in mind, so I wonder if it becomes more of an issue on very fast dobs (mine is f5).



It's strange though as the XW40-14mm supposedly have positive curvature, and XW10 and above have negative curvature, so you would expect whatever field curvature issues you had to resolve either in the 14 or the 10mm as they have opposite curvature from each other.


Just strange how we can have such different experiences with the same EPs.



Cheers,
Markus

Hi Markus,

I've owned all of the 1.25" Pentax XW's for about 20 years. The 14mm and 20mm both show field curvature in my 3 Newtonians. 18"/F4.5, 14"/F4.5 and 10"/F5.3. They show slightly less field curvature in the 10"/F5.3 than they do in the F4.5 scopes. While I can see it in the 10"/F5.3 the eyepiece is still very useable and performs very well. I find them still very useable in the F4.5 scopes as well, notwithstanding there is a bit more FC. They actually have less field curvature and astigmatism than the 17mm and 22mm Nagler T4's in all of my scopes when no paracorr is used.

Use a paracorr in any of the scopes and the field curvature completely disappears in the Pentax XW's and the Nagler T4's and they perform superbly. No idea what they do in refractors. I use those as finderscopes

Cheers
John B

[Stonius (Markus)]

Fair enough. Maybe I've never really noticed it because I always go paracorr on wider field EP's. The only time I don't is if I'm doing planetary work, when it's all about the center of the field anyway, and atmospheric dispersion plays a bigger role, to my mind.


Part of me feels like I should try harder to see if I can detect it in my scopes, but then I think what am I doing? I'm happy now. Why mess with happy? Why re-ignite that eternal lust for the perfect eyepiece? I guess it's all part of becoming a better observer, becoming more aware of the good and bad.



Cheers


Markus

Originally Posted by ausastronomer

Hi Markus,

I've owned all of the 1.25" Pentax XW's for about 20 years. The 14mm and 20mm both show field curvature in my 3 Newtonians. 18"/F4.5, 14"/F4.5 and 10"/F5.3. They show slightly less field curvature in the 10"/F5.3 than they do in the F4.5 scopes. While I can see it in the 10"/F5.3 the eyepiece is still very useable and performs very well. I find them still very useable in the F4.5 scopes as well, notwithstanding there is a bit more FC. They actually have less field curvature and astigmatism than the 17mm and 22mm Nagler T4's in all of my scopes when no paracorr is used.

Use a paracorr in any of the scopes and the field curvature completely disappears in the Pentax XW's and the Nagler T4's and they perform superbly. No idea what they do in refractors. I use those as finderscopes

Cheers
John B

[Don Pensack]

Originally Posted by stonius

i'm surprised to hear you say that. I haven't noticed this in any of my scopes, and i notice some of gear is broadly comparable. Sure the xw's have some field curvature, as all eyepieces do, but it's been below the threshold of detection for me. I'm much more bothered by chromatic distortion, atmospheric refraction, or even the barrel distortion in my tv pan24 (but that's another story - just don't pan with the pan!).

The 24mm panoptic doesn't have barrel distortion (negative rectilinear distortion), it has pincushion distortion (positive rectilinear distortion).
Barrel distortion bends lines like this as they cross the field: ( | ),
whereas pincushion distortion bends the lines like this: ) | (.
Otherwise, i agree about quick panning across a field when the rectilinear distortion has a high %.

Can i ask if its worse with certain scopes? Supposedly they're designed with refractors in mind, so i wonder if it becomes more of an issue on very fast dobs (mine is f5).

There is no reason to think these 85° eyepieces were designed for refractor use. The market for the eyepieces will be mostly reflectors and the first focal lengths in the series have been chosen with reflector focal lengths in mind. Few refractors are designed with focal lengths longer than 1000mm these days, where 1500-2500mm focal lengths are fairly common in reflectors.

It's strange though as the xw40-14mm supposedly have positive curvature, and xw10 and above have negative curvature, so you would expect whatever field curvature issues you had to resolve either in the 14 or the 10mm as they have opposite curvature from each other.

That would depend on the field curvature in the scope.

Just strange how we can have such different experiences with the same eps.

Observers' abilities to accommodate field curvature varies from person to person and diminishes with age. So it's not surprising some see none and others see a lot with the same eyepiece. And refractors inherently have more fc than reflectors, so if the curves of scope and eyepiece don't match, you can get some objectionable results.



Cheers,
markus

see my notes above.

[Don Pensack]

Oh,
Availability is supposed to be at the end of December.
I don't know Oz prices, but in the US, they'll be $479.95 (16.5mm) and $499.95 (23mm) respectively.

[ausastronomer (John Bambury)]

Originally Posted by Don Pensack

Oh,
Availability is supposed to be at the end of December.
I don't know Oz prices, but in the US, they'll be $479.95 (16.5mm) and $499.95 (23mm) respectively.

Are they your prices Don or US RRP ?

Cheers
John B

[Don Pensack]

Everyone will have the same price, John.
Ricoh short-margined the eyepieces to hit the price points.