Pentax XW 30mm and 40mm Return

[John]

The Pentax XW range seems to now include a 30mm and 40mm focal length in the 2 inch fitting again:

http://www.ricoh-imaging.co.jp/english/products/binoculars/scope/xw/index.html

In the US prices listed are $370 for the 30mm and $400 for the 40mm.

[alan potts]

I never had a chance to try either but both were very rare and I can't ever remember seeing a S/H 30mm and on only once a 40mm. I am sure they were both good eyepieces though for me the shorter end were at the very top of the game.

Alan

[DarkAntimatter]

I wonder how they would compare with a TV panoptic. 70 vs 68 degree fov; 20 vs 24mm eye relief. 

[omo]

FLO have them listed too: https://www.firstlightoptics.com/pentax/pentax-xw-30-r-2-eyepiece.html

[John]

2 hours ago, DarkAntimatter said:

I wonder how they would compare with a TV panoptic. 70 vs 68 degree fov; 20 vs 24mm eye relief. 

I have a 24mm Panoptic and some shorter focal length XW's. The 2 degree difference in AFoV is not really noticable to be honest with you. I have used a Pnetax XW 30mm and compared it with a Nagler 31mm and the UWAN/Nirvana 28mm. The Pentax was a really comfortable eyepiece to use and not as heavy as the others. Here is the report I compiled back then:

31nagler30xw28nirvana11-09.pdf

[michael.h.f.wilkinson]

I am seriously interested in the 40 mm, might well replace the Vixen LVW 42 mm I have three shorter XWs (5, 7, and 10 mm) and love them to bits. I quite like the Vixen LVW 42, but it nver was quite as comfy as the TMB Paragon 40mm I foolishly sold.

[michael.h.f.wilkinson]

I see FLO has them listed already:

https://www.firstlightoptics.com/pentax/pentax-xw-40-r-2-eyepiece.html

[Louis D]

I'm wondering how the 30mm XW compares to the 30mm APM UFF at almost twice the price.  As well, how the 40mm XW compares to the 40mm Meade 5000 SWA (Maxvision) at almost 4x the price I paid for the Meade.

[John]

4x the price usually equates to a few % difference in performance once you get above mid priced / mid market eyepieces I reckon. A lot of folks still go for those last few % though. Fussy lot, we are

Personally I'd be interested to know how the 40mm XW-R compares with my Aero ED 40mm which cost me £50 used.

[markse68]

Maybe we could “borrow” one and do a shoot out 😉 I’d be happy to loan my TV WF 40mm 😂

[Mr Spock]

Interesting design. Both the 30mm and 40mm are different from the rest of the range and from each other.

[Stu]

Interesting that they have been re introduced. Do I recall correctly that they have field curvature problems with certain scope types? Perhaps corrected for fracs but not newts??

[John]

3 hours ago, Mr Spock said:

Interesting design. Both the 30mm and 40mm are different from the rest of the range and from each other.

The XWs vary quite a bit in their optical design across the range of focal lengths. This chart includes the old 30mm and 40mm XWs but I think the optical design there is the same as the new release of those focal lengths:

Their optical characteristics show some variation across the range as well - some show negative field curvature and some positive:

[markse68]

What are the implications of field curvature? Is that the same as loss of focus at the edges?

[Rob Sellent]

Don't know if it helps but this might be a useful little picture guide, @markse68

[markse68]

Thanks Rob- very useful. I just realised that what I thought was coma was in fact astigmatism of the ep- little seagull stars at edge of field 

[Stu]

5 hours ago, John said:

The XWs vary quite a bit in their optical design across the range of focal lengths. This chart includes the old 30mm and 40mm XWs but I think the optical design there is the same as the new release of those focal lengths:

Their optical characteristics show some variation across the range as well - some show negative field curvature and some positive:

Any ideas why there is a difference John? Presumably they are all designed for similar scopes? The shorter focal lengths all have excellent reputations, seeming to imply negative FC is better in countering scope FC, but that must vary depending on scope type?

[jetstream]

I wonder if anyone can tell me how the 30mm XW compares to others, say an ES 82 30mm in the scatter department? I would love a truly low scatter, low power widefield eyepiece.

[Piero]

I read rumours about this a while ago on CN. Personally, I keep my 30mm APM UFF.

[John]

8 hours ago, Stu said:

Any ideas why there is a difference John? Presumably they are all designed for similar scopes? The shorter focal lengths all have excellent reputations, seeming to imply negative FC is better in countering scope FC, but that must vary depending on scope type?

I don't honestly know Stu. It used to be said that the XWs in the 1.25 inch fittied were originally designed for spotting scopes but I'm not sure about that. I doubt that you would use the 2 inch XWs in a spotting scope. The XWs replaced the XL range so the origins of the XLs are relevant as well. Interesting piece here on these ranges:

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

@jetstream / Gerry - I find the 1.25 inch XW's have pretty low levels of light scatter given their optical complexity so I think there is a good chance that the 2 inch ones will score well in this department too. The 5mm and 7mm XW are now my "goto" eyepieces for splitting Sirius and for that you want as little scatter as possible.

 

 

[Ships and Stars]

Oooh, that 40mm sounds wonderful!

(My non-technical contribution to this thread 😉 ! I've always been a Pentax camera and especially lens fan, never had the pleasure of trying out their EPs - soon I hope).

Edited December 10, 2019 by Ships and Stars

[John]

The 40mm would give you a 10mm exit pupil in your 20 inch dob. Might not be that effective ?

 

[Mr Spock]

A 40mm is going to be wasted with anything faster than f6. For an f4 scope 30mm is pushing it to the limit.

I guess that's why dob owners like the 21mm Ethos so much 

[Ships and Stars]

1 hour ago, John said:

The 40mm would give you a 10mm exit pupil in your 20 inch dob. Might not be that effective ?

 

 

15 minutes ago, Mr Spock said:

A 40mm is going to be wasted with anything faster than f6. For an f4 scope 30mm is pushing it to the limit.

I guess that's why dob owners like the 21mm Ethos so much 

True, you can't have it all. However, I had a 55mm TV plossl and it had something like a 13.5mm exit pupil at f4. Still had bright, razor sharp views. That was going to be paired up with a night vision tube, but would have been too bulky. 10mm exit pupil wouldn't be quite so bad but suppose the 30mm makes much more sense. There was an Ed Nagler article on the TV website discussing exit pupil, if I remember correctly he didn't seem too fussed if it was over 7mm. I'll dig that up. 

[Ships and Stars]

That article on exit pupil in excess of 7mm was on the TV myths website - apparently with refractors it's not an issue but indeed with reflectors the secondary can cause a black spot at really low magnification. For laughs I tried the 55mm plossl in a 130pds - no way, just a giant black spot, never had it in the 500p though. I would still have some overall light loss with a 40mm I suppose...

I'm keeping the 21E forever unless I become completely destitute however! It's an absolute winner.