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Pentax XW 40 - Optical Properties & Performance

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#1 rkelley8493

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Posted 19 September 2019 - 10:59 AM

I'm curious to know about the optical properties & performance of the Pentax 40 XW. I've been wanting to get one for my SCT for quite a while, but it will probably be another while longer before they're back in production. So until then.. maybe we can get this thread like the Apollo 11 until it hits the shelf lol.gif  Just kidding.. I wouldn't be able to read through 500 replies.

Anyways, how are the optical properties compared to the others of the Pentax XW line? Do they have the same or similar eye relief, neutral color, high contrast, and so on? What is the performance like in SCT's? Do they have field curvature, edge of field brightening, or other negative aspects? How is the size & weight? I imagine it's much less massive than the 41 Panoptic. What about their performance in other scopes like Dobsonians & refractors?

Comments about the 30 XW are welcome too! 


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#2 Scott99

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Posted 19 September 2019 - 11:10 AM

we just had a good discussion on this topic here:

 

https://www.cloudyni...-would-you-buy/


Edited by Scott99, 19 September 2019 - 11:11 AM.

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#3 csrlice12

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Posted 19 September 2019 - 03:13 PM

Have both the 30 and 40.....I like the 30 better, but both are "WoW" eyepieces.  The 40 in your SCT should be as good as the 30 in my dob.  These are some of the most comfortable to use eyepieces you will come across.


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#4 Starman1

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Posted 19 September 2019 - 04:40 PM

40mm: 6 elements.

Optical characteristics:

astigmatism, field curvature shown:

http://translate.goo...h/xo-xw/64.html

Transmission by wavelength:

http://translate.goo...h/xo-xw/63.html

 

 


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#5 Starman1

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Posted 19 September 2019 - 06:12 PM

I'm curious to know about the optical properties & performance of the Pentax 40 XW. I've been wanting to get one for my SCT for quite a while, but it will probably be another while longer before they're back in production. So until then.. maybe we can get this thread like the Apollo 11 until it hits the shelf lol.gif  Just kidding.. I wouldn't be able to read through 500 replies.

Anyways, how are the optical properties compared to the others of the Pentax XW line? Do they have the same or similar eye relief, neutral color, high contrast, and so on? What is the performance like in SCT's? Do they have field curvature, edge of field brightening, or other negative aspects? How is the size & weight? I imagine it's much less massive than the 41 Panoptic. What about their performance in other scopes like Dobsonians & refractors?

Comments about the 30 XW are welcome too! 

See my prior post for optical characteristics.

The 4 longer lengths of XWs have positive field curvature, but the 40 has very little, so it should perform quite well.

It doesn't quite have the edge performance of the 41mm Panoptic, but, as you mentioned, it's lighter.

So we'll see how much they sell for.


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#6 payner

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Posted 19 September 2019 - 07:43 PM

In using the 40-mm and the 30-mm XW, that was my finding. The 40 had some FC with the 30 being relatively considerable. I settled on the 41-mm Panoptic because it has proven clean to the edge in my telescopes.


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#7 junomike

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Posted 20 September 2019 - 07:02 PM

Had 30/40 XW, preferred the 31T5.  YMMV


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#8 John Huntley

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Posted 20 September 2019 - 07:09 PM

I've used a 30mm Pentax XW and it was very nice but not a "showstopper" in my opinion. I also enjoyed the Nagler 31mm more.


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#9 rkelley8493

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Posted 20 September 2019 - 11:18 PM

I've used a 30mm Pentax XW and it was very nice but not a "showstopper" in my opinion. I also enjoyed the Nagler 31mm more.

How about the color & contrast? Is it on the same level as the others in the XW line?



#10 vkhastro1

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Posted 21 September 2019 - 07:56 AM

Had 30/40 XW, preferred the 31T5.  YMMV

I previously owned the Pentax 40mm XL (twice), Pentax 30mm XW (twice) and Pentax XW (once).

I tried them in various scopes that I owned at different times including several hi-end triplet apos, TV127, Starmaster f/6 and f/5.4 Dobs (with and without a Paracorr), SCTs (Edge and XLT).

 

In multiple head to head comparisons to other competitors, I sold all of the Pentax eyepieces.

I have no inclination to repurchase them again.

 

Definitely preferred the TMB 40mm 68° or TV 41mm Panoptic (40mm competition) and the TV 31mm Nagler and APM 30mm UFF (30mm competition) or TV 35mm Panoptic (compromise one eyepiece in 30mm - 40mm range).

 

Still own the TV 31mm Nagler, TV 35mm Panoptic, TMB 40mm 68° and APM 30mm UFF.  Sold the TV 41mm Pan - preferred the TV 35mm version’s ergonomics.


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#11 junomike

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Posted 21 September 2019 - 08:30 AM

I previously owned the Pentax 40mm XL (twice), Pentax 30mm XW (twice) and Pentax XW (once).

I tried them in various scopes that I owned at different times including several hi-end triplet apos, TV127, Starmaster f/6 and f/5.4 Dobs (with and without a Paracorr), SCTs (Edge and XLT).

 

In multiple head to head comparisons to other competitors, I sold all of the Pentax eyepieces.

I have no inclination to repurchase them again.

 

Definitely preferred the TMB 40mm 68° or TV 41mm Panoptic (40mm competition) and the TV 31mm Nagler and APM 30mm UFF (30mm competition) or TV 35mm Panoptic (compromise one eyepiece in 30mm - 40mm range).

 

Still own the TV 31mm Nagler, TV 35mm Panoptic, TMB 40mm 68° and APM 30mm UFF.  Sold the TV 41mm Pan - preferred the TV 35mm version’s ergonomics.

I kept the 40mm Paragon also, however the 40mm XW was IMO still better than the 30mm XW.


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#12 areyoukiddingme

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Posted 21 September 2019 - 12:42 PM

I kept the 40mm Paragon also, however the 40mm XW was IMO still better than the 30mm XW.

 

I've made all the same comparisons, except for the 41 Pan and TMB, and agree with the conclusions on an optical basis.

 

But when it comes to using them, the XWs comfort and build quality does actually count for something. 

 

I think in part I just like a really clear, well-defined field stop and ease of use. When I don't have it, I'm a lot less satisfied, to the point that the field curvature, lateral color, and astigmatism matter less than they perhaps should.

 

Also, the XWs are not so good in fast scopes. I found that there were a near perfect match for the 6" F8 refractor I had. Even the field curvature practically disappeared in the 14 and 20.


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#13 Starman1

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Posted 21 September 2019 - 01:28 PM

Even to my old eyes, the FC of the 14mm and 20mm essentially disappeared in my coma-corrected f/5 (f/5.75 with CC) dob.

Effective focal length 1826mm (1.5x as long a FL as the 6" f/8 Scott mentions).

They even worked ok in a friend's 20" f/4 scope (f/4.6 with CC), but that also had a long FL: 2337mm.

The key seems to be a long focal length to yield a flat field.  The FC of the eyepiece is then minimal and can be ignored.


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#14 Jeff Morgan

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Posted 21 September 2019 - 02:12 PM

In 2010 I bought a new 40XW, with the idea of replacing a 41 Panoptic and 31 Nagler.

 

A beautiful eyepiece with great ergonomics and coatings. Much lighter than the competition too.

 

I really wanted to keep it, but it had substantially more field curvature than either of the Tele Vue eyepieces. So much so I thought it must have been a defective sample. The scopes were an 8" f/12 refractor and 12.5" f/6 Newtonian.

 

https://www.cloudyni...m-xw/?p=4064014

 

The Brown Truck operates in both directions, sadly the XW went back.


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