New 85 degree Pentax XWs on the way

[Don Pensack]

2 hours ago, markse68 said:

Hi Don, off topic sorry but is there a way to calculate the afov of an eyepiece given the field stop and focal length?

Mark

For a narrow field eyepiece, like an ortho, yes.  Then globular's formula works.

But it doesn't work for wide fields or ultra wide fields because distortion increases with apparent field (see chart).

And to calculate apparent field from field stop and focal length when distortion exceeds 10% (as it does on all wider fields) requires using distortion in the formula.

And unless we know the exact distortion %, the AFOV will not be accurate.

The best way to test the AFOV is the flashlight test:

https://www.cloudynights.com/topic/574401-an-easy-way-to-measure-apparent-field-of-view/?p=7958975

https://www.cloudynights.com/topic/574401-an-easy-way-to-measure-apparent-field-of-view/?p=7959408

Here is a chart showing how Angular Magnification distortion and rectilinear distortion increase with apparent field:

 

[Don Pensack]

More to the point, however, is that apparent fields in eyepieces, when tested, rarely deviate by more than 2° from the advertised value.

And truly, is 2° important?  Not really, even if comparing 40° to 42°.

So I think it is fair, unless the mfr specs have been tested and everyone knows the actual AFOV, just to assume the mfr's AFOV quote is correct.

Especially with the better grades of eyepieces discussed here on SGL.

[markse68]

Thanks Don, just checked a plossl that calculated by Globs method comes out at 55deg and using the flashlight method 57.4deg 

Mark

[Don Pensack]

In the flashlight test, remember the distance to the wall is measured from the exit pupil of the eyepiece, not the actual eyepiece itself.

I found it helps to use an aperture stop on the scope when doing the test, as this significantly reduces the size of the exit pupil and makes the exit pupil to wall measurement more accurate.

It also, by the way, makes measuring the eye relief of the eyepiece easier.

[HollyHound]

On 10/11/2022 at 18:05, Don Pensack said:

The XW85 will be a new series.  If successful, and I think they will be, it is likely these will only be the first focal lengths in the series.

This would be awesome… I have the full set of current XWs and they’re my primary set 😀

The XW 14 and 20 do have some field curvature in my f/7.5 and f/8 refractors, none in thr FOA-60Q (f/15) or Mewlon though!

The focal lengths are also pretty close to my existing two Masuyamas (16 and 26mm)… also 85 degrees and also some field curvature... Superb on axis though 👍

Certainly going to give these a try 🤔

Edited November 11, 2022 by HollyHound

[HollyHound]

On 10/11/2022 at 18:38, markse68 said:

They look like they will have the same removeable top section as the other XWs so probably have the 43mm thread that a TV Dioptrix could be mounted to?

That would be awesome… I have Dioptrx on my XW30 and XW40, and they attach and can be hidden within the rubber eyecup… very neat 😀

[HollyHound]

On 10/11/2022 at 10:45, markse68 said:

They’re huge though- heaviest in the lineup but i guess that was to be expected.

Heavy yes, but almost the same weight as the XW30 and XW40, and also all 2”… this could be the start of a fantastic matched set 🤔

[markse68]

15 minutes ago, HollyHound said:

Heavy yes, but almost the same weight as the XW30 and XW40, and also all 2”… this could be the start of a fantastic matched set 🤔

yes I am going to have to start saving

Mark

[HollyHound]

22 minutes ago, HollyHound said:

Heavy yes, but almost the same weight as the XW30 and XW40, and also all 2”… this could be the start of a fantastic matched set 🤔

Actually looking at the Astronomy Tools FoV calculator… the XW23 and XW30 are very close together on FoV, with the XW23 giving more magnification and better separation from the XW40 🤔

So perhaps the set becomes XW40, 23, 16 😀

[JeremyS]

26 minutes ago, HollyHound said:

Actually looking at the Astronomy Tools FoV calculator… the XW23 and XW30 are very close together on FoV, with the XW23 giving more magnification and better separation from the XW40 🤔

So perhaps the set becomes XW40, 23, 16 😀

Only one way to find out 😊

[Louis D]

44 minutes ago, HollyHound said:

Actually looking at the Astronomy Tools FoV calculator… the XW23 and XW30 are very close together on FoV, with the XW23 giving more magnification and better separation from the XW40 🤔

So perhaps the set becomes XW40, 23, 16 😀

I do tend to skip from a 40mm (Meade 5000 SWA, Pentax XW, or Lacerta ED) directly to either the 22mm NT4 or 17mm ES-92 (which have similar TFOV, 31.1mm FS vs. 27.4mm FS, respectively).  So yes, the XW23 might be a better fit with the XW40.

I'm guessing the XW23 will have a slightly larger field stop (FS) than the 22mm NT4, so maybe 32mm to 33mm.

Edited November 11, 2022 by Louis D

[Don Pensack]

I suspect 23mm will be the longest focal length because keeping up with Pentax's other set, the next logical focal length is 32-33mm, and that would be quite difficult to do in a 2" diameter eyepiece and keep it 85°.

Plus, it's difficult to see what they could bring to the table in terms of performance that the 30mm and 40mm XWs don't already offer.

If they end up being excellent eyepieces, a set of 23mm, 16.5mm, 12mm, 8.5mm, 6mm and 4.5mm would be a great progression.

[HollyHound]

1 hour ago, Don Pensack said:

Plus, it's difficult to see what they could bring to the table in terms of performance that the 30mm and 40mm XWs don't already offer.

If they end up being excellent eyepieces, a set of 23mm, 16.5mm, 12mm, 8.5mm, 6mm and 4.5mm would be a great progression.

Absolutely, the XW30 and XW40 (particularly) are superb eyepieces 👍

That set progression would be awesome 🤞😃

[Alan White]

On 10/11/2022 at 18:05, Don Pensack said:

Ricoh told me they have no intention to discontinue the 14mm and 20mm 70° XW.

The XW85 will be a new series.  If successful, and I think they will be, it is likely these will only be the first focal lengths in the series.

More of concern is that though they give a 20mm eye relief from the glass, they are stating only a 12mm eye relief from the rubber eyecup, ruling out glasses use.

If there is a way to modify the top and change the eyecup to yield more eye relief, then they would be sold to glasses wearers.

As soon as I get my hands on them, I will investigate this.

As someone who uses XW 70 in 10, 7 and 5 for astigmatism reasons and rather like the presentation of this range.
I am hopeful that the new 85 might work somehow, but to be honest a wider field is more useful in an undriven mount at higher magnifications.
Be interesting to see what this works out like in the real world use.

Hat off to Pentax to bring out a new line though and I hope it is highly sucessful for them even if it does not work for me.
Let's face it far more folks have non astigmatic eyes than those of us who do.

 

Edited November 12, 2022 by Alan White

[bingevader]

Maybe I'll hang on for the clones from EPsRUs!

[FLO]

On 11/11/2022 at 12:50, FLO said:

Here y'go 🙂 

Pentax XW 16.5mm 85°

Pentax XW 23mm 85°

ETA early-mid Dec.

Speaking with Pentax' distributor this morning, they advise us ETA for new Pentax XW 85-degree eyepieces is "mid-December" (a little later than our website's initial dispatch estimates). 

Thank-you for your patience, 

Steve 

[F15Rules]

I'm afraid the new ranges' sky high prices will exclude me, however good they are, and my experience with the XW30 put me off..

..but I must say, FLO were exemplary with their service and accepted my return without any issues whatsoever - so buy with confidence that you can return if you need to👍.

Dave

[HollyHound]

Many thanks for the updates… as you know, I’ve  placed an order for XW16.5 this morning and really looking forward to trying this new range out 😃

If it’s as good as I hope it will be, then the XW23 will be joining it very soon afterwards 🤞

[HollyHound]

6 minutes ago, F15Rules said:

I'm afraid the new ranges' sky high prices will exclude me, however good they are, and my experience with the XW30 put me off..

They’re certainly not cheap, but then neither are Nagler or Ethos… I’ve had all these, and whilst they’re lovely eyepieces, I much prefer the eye relief and ergonomics of my XWs 👍

Admittedly, the XW14, 20 and (less so) the 30, are let down a bit by field curvature, but they’re great in my Mewlon and I’m hoping the 16.5 and 23, will address even that FC issue 🤞

I can see a lovely set forming… 40, 23, 16.5 and then 10 downwards… although I would love to see some other focal lengths released later too, if these work out… 85 degrees is the max FoV for me now 😃

[markse68]

14 minutes ago, HollyHound said:

Many thanks for the updates… as you know, I’ve  placed an order for XW16.5 this morning and really looking forward to trying this new range out 😃

If it’s as good as I hope it will be, then the XW23 will be joining it very soon afterwards 🤞

Great- we have a guinea pig  Looking forward to your findings, though it might mean redesigning my XW case

Mark

[HollyHound]

5 minutes ago, markse68 said:

Great- we have a guinea pig  Looking forward to your findings, though it might mean redesigning my XW case

Mark

No worries… I’ll be putting this up against my XW14 and Masuyama 16, both of which do exhibit field curvature but have superb contrast and relaxing, comfortable views… if this new XW is as good as I hope, then these will likely be reserved for the “lightweight” set only 🤞

Apologies in advance if your case will need redesigning… mine too 🤣

[F15Rules]

I look forward to your thoughts and First Light, Gary👍..

The 16.5 and 23 do look intriguing and are clearly aimed to appeal to users of other high end brands..I think the 23mm is potentially the most interesting, as I've always found that focal length range (20-25mm) a really good match for my 1040mm fl scope. I've not tried a Panoptic 24mm, but know they are revered by many, and my personal favourite in the past was my lovely Vixen LVW 22mm, which ousted my XW 20mm due to the XWs FC, and just on the Vixens' overall sharpness and contrast.

Nowadays I have an excellent Axiom LX 23mm 82 deg, so that would be a fascinating comparo with the incoming  XW 23mm 85 degree, with very similar specs. I bet the Axiom is a good deal heavier though, although it is easily "decloaked".

If you'd care to do a side by side comparison at some point, I'd be happy to loan you my Axiom for that purpose 😊.

Good luck,

Dave

 

[Alan White]

2 hours ago, HollyHound said:

Many thanks for the updates… as you know, I’ve  placed an order for XW16.5 this morning and really looking forward to trying this new range out 😃

If it’s as good as I hope it will be, then the XW23 will be joining it very soon afterwards 🤞

Thank you Gary, be interested to know how this and the 23 do, then I can make the call on my aquired gap in my case once again being filled.
 

[HollyHound]

5 hours ago, F15Rules said:

I look forward to your thoughts and First Light, Gary👍..

The 16.5 and 23 do look intriguing and are clearly aimed to appeal to users of other high end brands..I think the 23mm is potentially the most interesting, as I've always found that focal length range (20-25mm) a really good match for my 1040mm fl scope. I've not tried a Panoptic 24mm, but know they are revered by many, and my personal favourite in the past was my lovely Vixen LVW 22mm, which ousted my XW 20mm due to the XWs FC, and just on the Vixens' overall sharpness and contrast.

Nowadays I have an excellent Axiom LX 23mm 82 deg, so that would be a fascinating comparo with the incoming  XW 23mm 85 degree, with very similar specs. I bet the Axiom is a good deal heavier though, although it is easily "decloaked".

If you'd care to do a side by side comparison at some point, I'd be happy to loan you my Axiom for that purpose 😊.

Good luck,

Dave

I'll certainly provide a report when I've had the chance to do the side by side comparison.... will be later in December now of course, but fingers crossed we get some clear skies over Christmas (as I'm off work for over a week) 🤞

I'm also very likely to get the XW23, as I want to put that up against both my XW20 and Masuyama 26mm... ok, they're either side in terms of focal length, but it's a focal length area I'm also very interested in... I did have the Nagler 22mm until quite recently, so will be good to see how it compares to that (from memory) 👍 

[markse68]

Has nobody got one yet? They’re out in America…

They have satin barrels like the XFs, and Don likes them

Mark

Edited December 22, 2022 by markse68