14mm Pentax XW or APM 12.5 Hi-FW

[Alan White]

I have a gap in my eyepieces and it down to two, both would sit with my mixed set of:
APM UFF 30, APM UFF 18, Pentax XW 10, Pentax XW 7 and others in shorter FL for the refractor.

So either the Pentax XW 14 and possible FC or
the APM 12.5 Hi-FW.
The varied FOV is not the driver, but is very similar caused by the differing EP FL, the quality of kit is the main driver, price works out very similar.

So here in the Blue Corner is:




So here in the Red corner is:

Any thoughts on this gang, please 

Edited September 20, 2020 by Alan White
typos of course

[Louis D]

I couldn't handle my 14mm Pentax XL's field curvature once I got presbyopia, so I replaced it with a 14mm Morpheus that has way less.  It's not quite sharp in the outer 15% of the field due to slight astigmatism and field curvature, but it's much more engaging with its measured 77° AFOV.  I've read that the 14mm XW suffers from the same field curvature as the 14mm XL, so you have to weigh that if your eyes are fixed focus.

That said, I rarely use any 14mm eyepieces because my 12mm ES-92 is so much more engaging than any of them and covers a larger TFOV.

I have thought about trying the Hi-FW, but it would be a niche player for use when I want to strictly stick with 1.25" eyepieces.

[Rob_UK_SE]

If you do decide to purchase the 14mm XW, they are currently being sold off as clearance on 365astronomy (£190) which is quite a discount. From the few reviews I have read, it seems the amount people that notice field curvature is quite dependent on the scope this eyepiece is paired with.

https://www.365astronomy.com/Pentax-XW-14mm-1.25-inch-Eyepiece.html

... not intending to confuse matters, but have you considered either the 14mm or 12mm Delos? I had the 14D for a time and found it went a little deeper on galaxies than the 13E (I only sold it because their focal lengths were so close). It was also extremely sharp across the entire field of view and very relaxing to use. 

Edited September 20, 2020 by Rob_UK_SE

[John]

I went for the Delos 14mm and 17.3mm because of the FC tales I'd read about with the XW 14mm and 20mm. They play well with the four shorter FL XW's that I have.

[Alan White]

4 hours ago, John said:

I went for the Delos 14mm and 17.3mm because of the FC tales I'd read about with the XW 14mm and 20mm.

But are they just tales or reality?
I have read such varied opinion on the XW 14 and 20.

[John]

1 minute ago, Alan White said:

But are they just tales or reality?
I have read such varied opinion on the XW 14 and 20.

I've experienced FC in other Pentax eyepieces (the XF's) and didn't like it so I was not prepared to take the chance that the frequent reports of FC from some very experienced observers in the 20mm and 14mm XW were untrue.

But I'd be very happy for you to try them and prove otherwise Alan

 

[Louis D]

4 hours ago, Alan White said:

But are they just tales or reality?
I have read such varied opinion on the XW 14 and 20.

Because it depends on your visual accommodation.  If your eyes are young, FC is not a big deal.  If you're old and suffering from presbyopia, it becomes an annoyance.  People really need to specify whether or not they suffer from presbyopia before commenting on FC.  This is true for both eyepiece FC and telescope FC.

[John]

9 minutes ago, Louis D said:

Because it depends on your visual accommodation.  If your eyes are young, FC is not a big deal.  If you're old and suffering from presbyopia, it becomes an annoyance.  People really need to specify whether or not they suffer from presbyopia before commenting on FC.  This is true for both eyepiece FC and telescope FC.

For the past 3 year or so I have needed to wear glasses for reading and close to clarity. So I guess I'm in that group ?

 

[Louis D]

@John Have you noticed any eyepieces or telescopes presenting out of focus edges that used to be in-focus?  This happened to me and my 14mm Pentax XL.  I had been using it for well over a decade when I noticed the edge didn't focus at the same point as the center about 6 years ago.  That was also about the same time I had to start wearing bifocals and computer glasses full time.  I was perplexed by how I had never noticed it before until I realized it was my eyes that had been compensating for the FC all those years.  I was a bit crushed realizing what I had lost.  Now I had to use flat field eyepieces in flat field scopes.

[alan potts]

The TV Delos is better in my view and I have had a few 14mm eyepiece, these two and the Meade 14mm UWA, that not a bad eyepiece in faster than F5 or so and in 10, I really liked it.

Alan

[John]

8 hours ago, Louis D said:

@John Have you noticed any eyepieces or telescopes presenting out of focus edges that used to be in-focus? 

I have not noticed this as yet Louis but during this Autumn I will be looking more critically at the views and I'll look out for this.

 

[Ricochet]

13 hours ago, Alan White said:

But are they just tales or reality?
I have read such varied opinion on the XW 14 and 20.

Taken in isolation, there is FC in every single XW, but how it presents itself will depend on the telescope it is paired with. There is also a difference in the "direction" of the FC between the short (3.5-10mm) and the long (14-40mm) XWs such that the short XWs will hide FC inherent in a telescope and the long ones will exacerbate it. In my dob, FC is noticable, but not not extreme, and with a touch of off-centre focusing, the field can be flattened if needed. In my spotting scope, which has an even flatter field than the dob, it appears flat to me in the centre 55-60°, with "acceptable" FC building up to about the 65° mark and then in the last 5° FC and astigmatism really kick in. 

In the dob, the other optical qualities of the 14XW are so good that the FC seems a small price to pay, remember that eyepiece design is a balancing act of distortions and aberrations and every design must have some issues. You could instead look at the similar 14 Morpheus, but we know that the alternative to FC is astigmatism, and in reports we see reports of reduced FC, but increased astigmatism. In your dob, you might find you have the same opinion as me, that the reports of FC are overstated, and the amount of FC is acceptable. However, this telescope has a radius of curvature of ~1200mm, which is quite flat, but you also have an ED doublet refractor that the eyepiece will be used with. This has a much smaller radius of curvature, somewhere in the region of ~265mm, and hence a much more curved field of its own. The combination of this type of scope and a long XW is exactly where you are going to see objectionable FC and so you are probably better off looking at other options. If I was to upgrade my 14XW for astronomical use I think I would be looking at a 14 Delos. Unfortunately, I don't know enough about the 12.5mm APM to hazard a guess as to how it would perform in comparison.

 

[F15Rules]

Hi Alan,

It won't come as a surprise to you but I didn't get on with the XW 14 and 20 due to the aforementioned FC, which really was noticeable to my 60+ eyes.

I've worn glasses for reading since I was 47. I've just had an extensive eye test and was told my distance vision is 20/20 but my close vision prescription has increased a little in my right eye, which I strongly suspected (hence my eye test). 

I don't need glasses for driving or observing.

I found the XWs at 10mm and less quite excellent, but for me the 14 and 20 were noticeably bested by the Morpheus 14mm and Vixen LVW 22 respectively (I know you loved the LVW 22mm too).

The Delos 14 gets great write ups but costs so much more than the Morpheus..I doubt my eyes could resolve any differences.

I don't know the APM range but they do seem to be gaining a good reputation with some well respected observers.

Your Vixen deserves top end eyepieces 😊👍.

Good luck with your choice..

Dave

[Alan White]

Thanks so far folks, that has helped me solidly discount the 14mm XW.
The explanations on Presbyopia*, which I have was the deal breaker, as was the helpful FC description.

So I now have a real dilemma, the APM 12.5, or something else, that being the Delos or Morpheus.
I tried a 12.5 Morpheus and it did not quite gel, but are all Morpheus equal?
Hmmm......

 

* I had to look up what this was,
which is age related close sight change, i.e. reading glasses.
 

[globular]

I can't advice you as I have no experience of these EPs - but I'm following this thread with interest as I have similar decisions to make.
If you're considering the APM Hi-FW 12.5 does that not also bring in the ES 92 12mm too?
Or have you ruled that out?  And if so what's your reason?

Edited September 21, 2020 by globular

[Don Pensack]

In my 12.5" f/5 with Paracorr II (which also adds a mild field flattening, I don't notice field curvature in the 14mm Morpheus, the 14mm XW, or the 12.5mm Hi-FW (all compatible with glasses)

and I have almost zero accommodation and have 3 different prescriptions of progressives for various purposes because of that.  I think the term is "fixed focus". LOL.

The key is that the effective focal length and radius of curvature of my scope is 1826mm, which is almost flat anyway, and with a mild field flattening, flat field eyepieces appear map-flat.

And eyepieces with field curvature appear flat, because FC in eyepieces is really small.

There are some exceptions (e.g. 35mm Panoptic), but field curvature isn't an issue, normally.

On the other hand, my 4" refractor has a 714mm focal length and 240mm radius of curvature and sees field curvature in a LOT of eyepieces.

It isn't, of course, field curvature in the eyepiece, but the scope, or, more exactly, the lack of a match between the FC of the scope and the FC of the eyepieces.

 

So it depends on your scope as to whether or not FC will be a problem.

A refractor?  Probably a problem.

A small newtonian (up to 10") used without a coma corrector?  Might be a problem.

A big newtonian used with a coma corrector--unlikely to be a problem.

Standard SCTs, with a curved focal plane--likely a problem.

New SCTs with corrective lenses installed--probably not a problem.

 

 

[Alan White]

13 hours ago, Don Pensack said:

In my 12.5" f/5 with Paracorr II (which also adds a mild field flattening, I don't notice field curvature in the 14mm Morpheus, the 14mm XW, or the 12.5mm Hi-FW (all compatible with glasses)

and I have almost zero accommodation and have 3 different prescriptions of progressives for various purposes because of that.  I think the term is "fixed focus". LOL.

The key is that the effective focal length and radius of curvature of my scope is 1826mm, which is almost flat anyway, and with a mild field flattening, flat field eyepieces appear map-flat.

And eyepieces with field curvature appear flat, because FC in eyepieces is really small.

There are some exceptions (e.g. 35mm Panoptic), but field curvature isn't an issue, normally.

On the other hand, my 4" refractor has a 714mm focal length and 240mm radius of curvature and sees field curvature in a LOT of eyepieces.

It isn't, of course, field curvature in the eyepiece, but the scope, or, more exactly, the lack of a match between the FC of the scope and the FC of the eyepieces.

 

So it depends on your scope as to whether or not FC will be a problem.

A refractor?  Probably a problem.

A small newtonian (up to 10") used without a coma corrector?  Might be a problem.

A big newtonian used with a coma corrector--unlikely to be a problem.

Standard SCTs, with a curved focal plane--likely a problem.

New SCTs with corrective lenses installed--probably not a problem.

 

 

@Don Pensack,Just to check are you in the it depends bit referring to all 3 eyepieces?

Small 10" Newtonian!!!! I thought I was a 'real' observer when I got that scope! 😉

[Don Pensack]

People have reported field curvature in both the 14mm Morpheus and the 14mm XW.

I mentioned those because I think the visibility of field curvature is related to accommodation (of which I have none) and the type and focal length of scope.

And newtonians of fast focal ratio can display some field curvature up to about a focal length of 1200mm if the field curvature of the eyepiece doesn't match the scope.

I wasn't implying a 10" scope is a small scope, but it can be short enough to reveal field curvature which is less seen in longer instruments.

[Alan White]

Guess what, I have decided on neither in my initial list of this post,
does sound familiar?

Going for the Morpheus 12.5 for glasses friendly and sits better in my steps of magnification on both of my scopes.
Funnily I tried one as a loaner a while back and bought the 10XW, but knew I needed a 12.5mm.
Final call made, placed an order with the forum sponsor 😁

Edited September 24, 2020 by Alan White