Which would you keep, Pentax XW or Myriad MWA 5mm?

[Mike_S]

Hi,

I was reallt struggling to decide between these two for my 10” F4.7 dob, I ordered the Myriad as it was cheaper then I was offered a good deal on the Pentax XW that I basically cant lose money on. I felt I couldnt turn down so now i can try both to see for myself when they arrive this week. However Ive just read that the Myriads are not weather proof? Is this normal with quality Eyepieces or is it probably more of a case that the likes of Pentax XW and ES 100 degree that i was also considering are just better quality? I dont plan on keeping both of them long term but you never know. 

[jetstream]

XW.

[Louis D]

I've had the 5.2mm Pentax XL for 20 years and still love using it to bust globulars.

[Demonperformer]

I just love the Pentax lenses, so would pick that one any day, they won't let you down ... but then, I haven't tried the Myriad!

[Mike_S]

I think the fact that the remaining stock of Myriads is running out plus they look such good value at the moment and they never come on sale made me want to try them. Plus Pentax XW’s for £180 posted only two months old I thought was a steal. Will see! Do you think it will be a problem that they aren’t weather proof though? Is this a reason they have gone out of production perhaps? Maybe I will not like the smaller eye relief or maybe I won’t be able to tell the difference optically and I’ll prefer the field of view.

[Demonperformer]

It depends on how "not weather proof" they are. You are unlikely to be observing in a downpour, but if it means that the slightest hint of dew is going to get on the inside surfaces and never leave, that I would consider to be a major drawback. Was it online that you found this comment? A link to see exactly how it was said and in what context may help provide a more constructive answer.

[Mike_S]

It was on another forum. Somebody just said they weren’t weatherproof. I’ll try to find it again later. Yes I’m not going to be using them in a downpour but I’m concerned about dew getting behind the lens.

[JOC]

I've not used the Myriad, but I do own a Pentax XW 5mm.  OK - you've got a bigger more light gathering scope than my 8" one, but I'm struggling to find occasions when mine is better than anything else I've got (you will see in my signature that I've got a good few to pick from).  OK, perhaps weather conditions also play a part, but I find it needs a very bright object to get it to work.  Perhaps because of the high Magnification, but I find it really makes the image dim, I also find (somewhat surprisingly given its XW characteristic) that, in comparison, to some of my other EP's that I need to far more accurate in terms of getting my eye straight above it before I can see through it.  I did get it on a cluster the other week and it did start to open it up, but so far I haven't been as impressed with it as I expected to be given what folks say about them.  I am persisting though.

[Stu]

1 hour ago, JOC said:

I also find (somewhat surprisingly given its XW characteristic) that, in comparison, to some of my other EP's that I need to far more accurate in terms of getting my eye straight above it before I can see through it

Have you tried adjusting the eyeguard upwards? They are a twist up if I remember correctly.

At x240 in your 8" (assuming 1200mm f/l) you are at 0.8 ish 'll exit pupil which will certainly dim things down, that's not the eyepiece, just physics! Most likely useful for planets, moon and doubles, probably too much for globs itbwould think.

To the OP, I would give them both a good try out to see which you favour. Outside afov, everything says that the Pentax should be the winner, but you may favour the ergonomics or just get on better with the Myriad so give it a go!

[JOC]

2 minutes ago, Stu said:

Have you tried adjusting the eyeguard upwards? They are a twist up if I remember correctly.

At x240 in your 8" (assuming 1200mm f/l) you are at 0.8 ish 'll exit pupil which will certainly dim things down, that's not the eyepiece, just physics! Most likely useful for planets, moon and doubles, probably too much for globs itbwould think.

I've given it a twist - yes it does make a difference - I'll have to see if any of the other EP's do something similar!  I didn't know they did that.

I did put it on Mars and it did give me a lovely view and it did split the double double really well so I think you are right.  240x yes, correct assumptions 1200mm f/l.  Well at least it's physics making it dim and not just me (I began to wonder if I had a faulty EP), though if the exit pupil can be so small on a half decently sized telescope it does make me wonder why they offer such a large expanse of glass at the top of the EP to look through!

[Stu]

2 hours ago, JOC said:

though if the exit pupil can be so small on a half decently sized telescope it does make me wonder why they offer such a large expanse of glass at the top of the EP to look through!

That will be related to the apparent field of view and potentially also eye relief, although I'm less sure of the relationship for the latter. It is obviously not related to exit pupil (which obviously also changes with scope aperture) as my 5mm BGO would give the same whilst having an exit lens the size of a very very small thing!

EDIT Quite a few eyepieces, though not all by any means have some form of extendable eyeguard, either pull up or twist up. Particularly the ones with longer eye relief as if you do not use glasses it can be a challenge getting your eye in the right place. TV Plossls such as the 32mm and 40mm benefit from the outrageously expensive but very good eyeguard extenders you buy separately. Some are not even obvious that they have this facility, like the 41mm Panoptic, I never discovered it until after I had sold it!

[Louis D]

3 hours ago, JOC said:

though if the exit pupil can be so small on a half decently sized telescope it does make me wonder why they offer such a large expanse of glass at the top of the EP to look through!

To allow 20mm of usable eye relief at a 70 degree AFOV requires a very large eye lens.  It's simple trigonometry.  20mm is the adjacent side, 70/2=35 is the angle, so solving for the opposite side, 20*tan(35)=14mm.  Times two to get the entire width of the eye lens (2*14)=28mm minimum diameter.  In reality, the eye lens is about 35mm in diameter on Pentax XWs due to optical design and physical packaging issues.

[JOC]

3 minutes ago, Louis D said:

To allow 20mm of usable eye relief at a 70 degree AFOV requires a very large eye lens.  It's simple trigonometry.  20mm is the adjacent side, 70/2=35 is the angle, so solving for the opposite side, 20*tan(35)=14mm.  Times two to get the entire width of the eye lens (2*14)=28mm minimum diameter.  In reality, the eye lens is about 35mm in diameter on Pentax XWs due to optical design and physical packaging issues.

And yet if the exit pupil is only 8mm that in theory means that in such a large expanse of glass you can only really use a 8mm diameter and have to be right over the top of that.  I can't fault the trigonometry, but it still seems a bit nuts!

[Mike_S]

Finally got them both. Tried the Myriad on jupiter last night. The view was much darker than though my cheap Plossls but I could see more because of a lot less glare. Just need some clear nights to compare both now. The eyecup seems too large on the Myriad. My eye just fits right through and eyelashes get in the way. I don’t wear glasses. I can get used to it I suppose. I don’t know why the glass is bigger at the front on the Pentax when the AFOV is less?

[John]

I feel that the Pentax XW 5mm is the better performing eyepiece than the Myriad 5mm. Not by a lot (as my review says !) but enough to give the XW the permanent place in the eyepiece case. I've also compared the XW 5mm to the Tele Vue Ethos 4.7mm and, following around 12 months of comparison, the XW was just a touch better there as well, just.

The size of the eyelens is not a guide to the apparent field of view. The field stop, which is an aperture ring within the eyepiece, is what determines the field of view. The larger eye lens of the Pentax is probably more to do with maintaining the 20mm of eye relief.

The weatherproof issue is not something that bothers me at all. No Tele Vue eyepieces carry that standard but they don't seem to be held back by that in any way

On the Pentax XW eyecup, if you wear glasses when observing, the eyecup should be in it's lowest position. If you do not wear glasses, the eyecup needs to be in, or towards, it's upper position. There is around 10mm or so of travel between the 2 eyecup positions.

What really matters though, is what YOU think of them. Give yourself several sessions to compare them and use a range of targets to do so. They are both very well made eyepieces so the differences (apart from the field of view) might not be apparent initially.

 

 

 

[Louis D]

1 hour ago, MSammon said:

I don’t know why the glass is bigger at the front on the Pentax when the AFOV is less?

The real question is why the Myriad claims 15mm of eye relief and 110 degrees of field with a roughly 30mm eye lens.  Doing the calculation I mentioned in my earlier post, the Myriad would require at least a 43mm eye lens to have 15mm of eye relief and a 110 degree field.  That's the same size as the ES-92 eyepieces's eye lenses.  Clearly, the Myriad has more like 10mm of eye relief if it has a 110 degree field.

2 hours ago, MSammon said:

My eye just fits right through and eyelashes get in the way.

Everyone complains the Myriad top's design is very poor because it is too wide.  Some folks can't get in close enough to see the entire field without tipping their head sideways to fit it past their nose.  That's why the Lunt/APM version is much more well reviewed because of their tapered tops and narrower eye cup.

[Mike_S]

Thanks guys very interesting. I’m going to give these a few sessions  at least. I’ve also been tying to compare Pentax XW to Delos. I hear Delos better in focul lengths > 10mm  but Pentax more comfortable and just as good <10mm? Really intrigued to try one of them as well