Pentax XW 5mm

[markse68]

16 minutes ago, John said:

https://www.sciencecenter.net/hutech/pentax/ep.htm

thanks John! 

[John]

I've not encountered an XL so I've not had the opportunity to compare one with the XW's.

I suppose after finding that the T6 Naglers were a step up in performance from the T1 and T2 Naglers I've thought that the XW's might provide subtle improvements over their predecessor range but I've not had the opportunity to find out for myself as yet.

We are up amongst the top tier with all of these I reckon though. Vixen LVW's probably up there as well. Vixen need a really good 70 degree line again IMHO.

[John]

One interesting thing about the XW's is that they use special coatings on the cemented lens surfaces as well as the glass-to air ones to maximise transmission and minimise scatter. I think some others use this technique now. Not sure if the XL's did or not ?

 

[markse68]

7 minutes ago, John said:

One interesting thing about the XW's is that they use special coatings on the cemented lens surfaces as well as the glass-to air ones to maximise transmission and minimise scatter. I think some others use this technique now. Not sure if the XL's did or not ?

 

well they mention “special coating” on all but the 40 in the data sheet I found so maybe- whether it’s the same though is anyone’s guess 

[markse68]

40 minutes ago, johninderby said:

Interesting 🤔

https://astromart.com/reviews-and-articles/reviews/eyepieces/other/show/understanding-pentax-xl-and-xw-eyepieces

why would you do that ?!?😳

[johninderby]

3 minutes ago, markse68 said:

why would you do that ?!?😳

Must have been very bored. 😁

[markse68]

this is a weird statement- what could they be referring to?

[JeremyS]

8 minutes ago, markse68 said:

why would you do that ?!?😳

...don't do this at home 🤣

[Louis D]

5 hours ago, markse68 said:

Do you know what year they were released?

According to this website and Bill Paolini's eyepiece book on page 14, 1996 seems to be the agreed upon year for the XLs.  The XWs came out in 2003.

[Louis D]

2 hours ago, markse68 said:

why would you do that ?!?😳

To increase the distance between eyepieces for binoviewer usage.  Not everyone has wide set eyes and/or a narrow nose bridge.  Some folks decloak the already narrow TV Delites because their nose is too big to fit between them.

[Louis D]

3 hours ago, John said:

https://www.sciencecenter.net/hutech/pentax/ep.htm

Awesome sauce! 🤩

Putting them side by side makes it easier to see the changes from one line to the next.

Probably the most novel XW contribution was the introduction of the intermediate lens between the negative and positive groups in the 7mm, 10mm, and 14mm versions.  Something similar was used in the Ethos and ES-100 eyepieces a few years later:

I would guess it helps to realign and corral the ray bundles as they are being spread out on their journey from the negative group to the positive group.  However, I don't know if it field flattens, reduces astigmatism, reduces chromatism, or a does little bit of each.  Perhaps @Ruud might know.

[Alan White]

On 01/07/2020 at 09:32, JeremyS said:

Thanks Louis. I've got the complete set of Pentax XL's, which I've owned from new. This includes the rare, but narrower afoev, 28mm. I've never used an XW, so there is always the nagging suspicion that they must be much better..... 

Until today I did not realise that the xl 28 mm was narrower fov.... is it 1.25” by any chance?

[JeremyS]

3 minutes ago, Alan White said:

Until today I did not realise that the xl 28 mm was narrower fov.... is it 1.25” by any chance?

Yes it’s 1.25” Alan. 
Nice eyepiece, though.

[Alan White]

Thanks Jeremy, that would explain the FOV then.

Pentax do make fine glass.

 

Edited August 16, 2020 by Alan White

[JeremyS]

6 minutes ago, Alan White said:

Thanks Jeremy, that would explain the FOV then.

Pentax do make fine glass.

 

And wonderful coatings for them  too 👍

Edited August 16, 2020 by JeremyS

[Alan White]

And let’s not forget the Build Quality too.

[Alan White]

Oh and JID has so far not fitted a handle his one yet..... but time will tell 😉

[johninderby]

Hmmmmmmm 🤔

[John]

10 minutes ago, Alan White said:

Oh and JID has so far not fitted a handle his one yet..... but time will tell 😉

They have a handle built in - you hold them like an ice cream:

[johninderby]

7 minutes ago, John said:

They have a handle built in - you hold them like an ice cream:

Please don’t start a lickable eyepiece thread. One lickable thread is enough . 🙀🙀🙀

[Alan White]

12 minutes ago, johninderby said:

Hmmmmmmm 🤔

I knew it was dangerous suggesting such a thing...

[johninderby]

Be carefull what you wish for. 😁😁😁😁😁