40 replies to this topic

[Gastrol]

I’m not really seeing much if any FC with either one. Maybe some with the ES (I suppose inherent FC from the scope will be more obvious with wider AFOV). I see some RD, especially with the ES as expected. The ES has wider AFOV so it will have more RD. Plus the XWs are designed with spotting scope use in mind, so they don’t have as much RD. Better for terrestrial observing that way.

It is interesting, because everyone knows a F5 refractor has field curvature, and everyone knows the 20XW has field curvature. But that is a really sharp looking field stop to me. I almost wonder if the FC in the XW might be opposite and be canceling out the FC in the refractor? The XWs were made with spotting scopes in mind so it might not be a huge leap to think they might have designed in some FC in order to cancel out the FC in a typical F6 spotting scope.

Scott

Oops...maybe, perhaps I’m confusing FC to pin cushion distortion..  

 

Edit:   I deleted the photos as didn’t want to confuse anyone.

Edited by Gastrol, 23 February 2021 - 01:28 PM.

[Sarkikos]

If the image is sharp from center to edge, there is no FC.  That's all that counts.  There can still be barrel or pin cushion distortion.

 

But ... if the camera has deep depth of focus, it might not show FC that a human observer can see. 

 

Another reason why I take what a camera shows with a grain of salt.  I go by what my eye shows ... as long as I'm wearing my eyeglasses or a Dioptrx is on the eyepiece.

 

Mike

Edited by Sarkikos, 23 February 2021 - 12:26 PM.

[BillP]

I’m not really seeing much if any FC with either one.

I agree.  I definitely do not think that the XW20 or XW14 have a FC "problem"   I gave up a 24 Pan because I liked the 20XW better.  Yes it can show some FC on the far off-axis, but just depends.  I use f/8 refractors and never really even notice it.  And in my Dob when the Paracorr is in place and set properly none ever comes to my attention.  Many are so concerned about the far off-axis that you would think that the central region has no meaning!  That however is what I consider the most important region and why I have XWs and Morpheus as my wide field choices.

 

FWIW, before I got the 14XW I kept hearing folks talk about its "problem" as well.  When I got it I actually thought that maybe Pentax changed the optical prescription because there was no problem to be seen in my scopes (f/8 Apos and f/4.7 Dob w/Paracorr).  Funny though that hardly anyone mentions all the RD distortion in the off-axis of most wide fields (XWs have comparatively little in comparison).  Guess no one cares when the see straight rilles, walls, and the lunar terminator on the Moon appear curved like a bow, or how the relative position of stars in the field are all incorrect in the off-axis. I don't know, maybe they think that is the way those features look in reality!  Go figure.

Edited by BillP, 23 February 2021 - 10:58 PM.

[Deep13]

The 20 XW is nice and clear and sharp on axis, but it has a lot of field curvature. The 24 Pan does not, though it may have some pin cushioning.

 

Of those two, I'd get the 24 Pan no question. There is also a 19 Pan, FYI.

[Sarkikos]

The 20 XW is nice and clear and sharp on axis, but it has a lot of field curvature. The 24 Pan does not, though it may have some pin cushioning.

 

Of those two, I'd get the 24 Pan no question. There is also a 19 Pan, FYI.

I'd agree, except for the short eye relief on the 24 Pan.  Like I've said before, although relatively short eye relief is not a big deal to me, I somehow expect the eye relief to be longer on a 24mm eyepiece.  To be comfortable viewing through the 24 Pan, I need to take off my glasses, which I shouldn't have to do with a 24mm eyepiece.  When I take off my glasses, the view is not corrected for my astigmatism, which kicks in with a 24mm eyepiece.  But if I put a Dioptrx on the 24 Pan, there goes the eye relief. 

 

Mike

Edited by Sarkikos, 24 February 2021 - 07:55 AM.

[Sarkikos]

I agree.  I definitely do not think that the XW20 or XW14 have a FC "problem"   I gave up a 24 Pan because I liked the 20XW better.  Yes it can show some FC on the far off-axis, but just depends.  I use f/8 refractors and never really even notice it.  And in my Dob when the Paracorr is in place and set properly none ever comes to my attention.  Many are so concerned about the far off-axis that you would think that the central region has no meaning!  That however is what I consider the most important region and why I have XWs and Morpheus as my wide field choices.

 

FWIW, before I got the 14XW I kept hearing folks talk about its "problem" as well.  When I got it I actually thought that maybe Pentax changed the optical prescription because there was no problem to be seen in my scopes (f/8 Apos and f/4.7 Dob w/Paracorr).  Funny though that hardly anyone mentions all the RD distortion in the off-axis of most wide fields (XWs have comparatively little in comparison).  Guess no one cares when the see straight rilles, walls, and the lunar terminator on the Moon appear curved like a bow, or how the relative position of stars in the field are all incorrect in the off-axis. I don't know, maybe they think that is the way those features look in reality!  Go figure.

So it boils down to what you are willing to tolerate.  Some don't want FC in the outer field.  Others don't want RD.  Still others don't want AMD.  In any case, you can always move the object to the center of field to have a view without FC, RD or AMD.  For FC you can refocus for center or edge of field, but that gets old real fast.  And splitting the difference by focusing midway between center and edge doesn't always work.

 

Personally, I'd rather not have any of these aberrations or distortions anywhere in the view.  But I'd much rather have RD or AMD, than a fuzzy outer field due to FC.  

 

Mike

Edited by Sarkikos, 24 February 2021 - 07:53 AM.

[25585]

Vixen LVW 22mm is still the best low 20s 1.25" eyepiece, if you can find one. APM 24mm UFF is its modern equivalent, owning both.

[BillP]

The 20 XW is nice and clear and sharp on axis, but it has a lot of field curvature. The 24 Pan does not, though it may have some pin cushioning.

"Some" pincushing ... that's an understatement

[BillP]

So it boils down to what you are willing to tolerate.  Some don't want FC in the outer field.  Others don't want RD.  Still others don't want AMD.  In any case, you can always move the object to the center of field to have a view without FC, RD or AMD.  For FC you can refocus for center or edge of field, but that gets old real fast.  And splitting the difference by focusing midway between center and edge doesn't always work.

 

Personally, I'd rather not have any of these aberrations or distortions anywhere in the view.  But I'd much rather have RD or AMD, than a fuzzy outer field due to FC. 

Very true.  There are no absolutes here.  AMD is not better or worse than RD, both distort the view.  The off-axis is not more important than the on-axis and the character of the on-axis view is indeed different among different eyepieces (but less obvious that off-axis distortions why most seem to not take note).  All boils down to what is tolerable for each individual and of course personal preferences.

Edited by BillP, 24 February 2021 - 01:35 PM.

[Starman1]

I'd agree, except for the short eye relief on the 24 Pan.  Like I've said before, although relatively short eye relief is not a big deal to me, I somehow expect the eye relief to be longer on a 24mm eyepiece.  To be comfortable viewing through the 24 Pan, I need to take off my glasses, which I shouldn't have to do with a 24mm eyepiece.  When I take off my glasses, the view is not corrected for my astigmatism, which kicks in with a 24mm eyepiece.  But if I put a Dioptrx on the 24 Pan, there goes the eye relief. 

 

Mike

Which is why the 24mm I'm using in my apo, now, is an APM UFF.

[Starman1]

As a lunar viewer, I stick to narrower eyepieces to avoid excessive distortion of the wider fields (which, due to the laws of physics, they will have).

I max out at about 65°

 

In the dob, though, I prefer the wider fields, which gives me a choice of the distortion characteristics, but not a choice of the absence of distortion.

That means either a lot of AMD or a lot of RD, and I prefer the separations between stars to stay the same at the edge and objects to remain the same size,

which puts me down in the RD camp, where AMD is minimized or banished.

 

So the distortion in the 24mm Panoptic never bothered me because the eyepiece is very sharp from edge to edge.

The dilemma is as Mike described in post 30, and why I reluctantly let the 24mm Panoptic go.

 

If you're bothered by having any distortion in eyepieces, stick to Abbe Orthoscopics.

However, they aren't free of astigmatism in the outer field.

 

There's no perfect eyepiece.

[Sarkikos]

Which is why the 24mm I'm using in my apo, now, is an APM UFF.

I have the 30 APM UFF.   It has a very flat field with no obvious RD or AMD, at least to my eyes and viewing style.  The 24 APM UFF will probably be my next eyepiece acquisition.  Then I'll have a bioviewing pair of  24 Pans to sell.

 

Mike

Edited by Sarkikos, 24 February 2021 - 02:43 PM.

[25585]

What are 20 XWs like for binoviewing?

[Starman1]

I have the 30 APM UFF.   It has a very flat field with no obvious RD or AMD, at least to my eyes and viewing style.  The 24 APM UFF will probably be my next eyepiece acquisition.  Then I'll have a bioviewing pair of  24 Pans to sell.

 

Mike

Mike,

Try the 30mm UFF on telephone poles or the edges of buildings.  It has RD, which is typical for an astronomical eyepiece.

The 24mm does too, though with a narrower field, it's less.

[rhcrooks]

LVW22 is the most comfortable EP I have ever viewed through - the Pan 24 is better overall. I have them both and I couldn't ever part with either. I have the Pentax 10 - never really used the 20... but if it's anything like the 10 it's an oversized utilitarian beast when compared to the 24 Panoptic to be sure.

 

The 24mm Panoptic is the one you want - it's a classic for a reason.

[213Cobra]

22mm Panoptic betters my 20mm Pentax-XL on visual acuity across the board. These are not night and day differences. But nevertheless discernible. And Panoptic better accommodates DioptRx too. So limiting yourself to current production, the 24mm Panoptic gets the nod in a more compact size. Or you can step to the 24mm Nagler.

 

The 22mm Panoptic is the classic. The 24mm Panoptic is perhaps a modern classic.

 

Phil