Pentax XW 16.5mm and 23mm 85 degree eyepieces

[Don Pensack]

Louis,

I can use the TeleVue Apollo 11 with glasses on (it's not too difficult), and that one has 18mm of eye relief from the glass and 14.3mm from the folded-down rubber eyecup.

The 85° Pentaxes, though have only 12mm from the rubber.  Some who have shallow eyes and a short eye-to-glasses distance might be able to use them.  I could not do so comfortably,

but only by mashing my glasses into my eye socket until my eyelashes brushed the glasses.

The picture from "globular" of the 16.5mm shows why--there is a lot of aluminum above the lens to mount the eyecup onto.

With a different eyecup design, that aluminum top could have been 3mm shorter.  But, as it sits, even if the eyecup is removed it still has less than 14mm of eye relief, alas.

[Louis D]

Too bad for Pentax.  I've been fishing around for a Father's Day gift to myself, and the 23mm was one possibility.  I'll continue to give it a hard pass since Don and I seem to have similar eye socket depth.

C'est la vie.

[Legalpusher]

I am new to astronomy.
While searching for suitable eyepieces for my newly acquired Dobsonian,  I came across the Pentax 16.5 and 23.  My experiences with Pentax in my youth prompted me to buy them.  Compared with the OEM Celestron Omni 32mm,  I was happy with the purchase, and added the 40mm XW as well.  They were comfortable enough to use with glasses, although is much more comfortable without the glasses in between.  A months later, I bought a Tele-Vue Ethos 8mm, the 100 degrees AFO blew me away, I bought the 6mm as well.  They were comparable in comfort and view quality.  The wider view gave them a unique feel.  Don’t think I’ll be buying the 4.7mm soon.  The lack of funding, a common condition since I acquired the hobby, & the weather doesn’t favor its use, maybe later in the fall.  
The 4.7 TeleVue at 110 degree of apparent field of view probably won’t be used frequently due to condition limitations.  Should I buy a less costly alternative like a Nagler, Pentax XW, or skipping it totally?  May be a Powermate?  Having 4 mm and 3 mm eyepieces with the same field of view at the cost of 1/2 an Ethos is appealing.  What pitfalls am I not aware of? If any?
Waiting for a $40, 100mm Vixen eyepiece to replace my OEM red dot finder.  My arthritis prevents me from using it since day 1 totally.   How anyone able to use it on a Dobsonian is beyond my comprehension.  Can’t wait to see how it works out.   May be I should replace the red dot with a right angle finder for $80 instead?

 

 

[michael.h.f.wilkinson]

6 hours ago, Legalpusher said:

I am new to astronomy.
While searching for suitable eyepieces for my newly acquired Dobsonian,  I came across the Pentax 16.5 and 23.  My experiences with Pentax in my youth prompted me to buy them.  Compared with the OEM Celestron Omni 32mm,  I was happy with the purchase, and added the 40mm XW as well.  They were comfortable enough to use with glasses, although is much more comfortable without the glasses in between.  A months later, I bought a Tele-Vue Ethos 8mm, the 100 degrees AFO blew me away, I bought the 6mm as well.  They were comparable in comfort and view quality.  The wider view gave them a unique feel.  Don’t think I’ll be buying the 4.7mm soon.  The lack of funding, a common condition since I acquired the hobby, & the weather doesn’t favor its use, maybe later in the fall.  
The 4.7 TeleVue at 110 degree of apparent field of view probably won’t be used frequently due to condition limitations.  Should I buy a less costly alternative like a Nagler, Pentax XW, or skipping it totally?  May be a Powermate?  Having 4 mm and 3 mm eyepieces with the same field of view at the cost of 1/2 an Ethos is appealing.  What pitfalls am I not aware of? If any?
Waiting for a $40, 100mm Vixen eyepiece to replace my OEM red dot finder.  My arthritis prevents me from using it since day 1 totally.   How anyone able to use it on a Dobsonian is beyond my comprehension.  Can’t wait to see how it works out.   May be I should replace the red dot with a right angle finder for $80 instead?

 

 

What sort of Dobson do you have? in an 8" F/6 a 3mm EP is not that useful. I also find that in my 8" scope (F/10) I do not use my Pentax XW 5mm , although it does get used in the 80mm F/6 APO I have. I also find that the wider FOV is most useful at the lower magnifications, but for planetary work, the 70 deg FOV of the XWs is more than enough.

Finder-wise: I would go for a RACI finder. I have a 9x50 and a big 14x70 (home made) and they are so much better to use than an RDF or straight-through finder

[Don Pensack]

6 hours ago, Legalpusher said:

I am new to astronomy.
While searching for suitable eyepieces for my newly acquired Dobsonian,  I came across the Pentax 16.5 and 23mm  My experiences with Pentax in my youth prompted me to buy them.  Compared with the OEM Celestron Omni 32mm,  I was happy with the purchase, and added the 40mm XW as well.  They were comfortable enough to use with glasses, although is much more comfortable without the glasses in between.  A months later, I bought a Tele-Vue Ethos 8mm, the 100 degrees AFO blew me away, I bought the 6mm as well.  They were comparable in comfort and view quality.  The wider view gave them a unique feel.  Don’t think I’ll be buying the 4.7mm soon.  The lack of funding, a common condition since I acquired the hobby, & the weather doesn’t favor its use, maybe later in the fall.  
The 4.7 TeleVue at 110 degree of apparent field of view probably won’t be used frequently due to condition limitations.  Should I buy a less costly alternative like a Nagler, Pentax XW, or skipping it totally?  May be a Powermate?  Having 4 mm and 3 mm eyepieces with the same field of view at the cost of 1/2 an Ethos is appealing.  What pitfalls am I not aware of? If any?
Waiting for a $40, 100mm Vixen eyepiece to replace my OEM red dot finder.  My arthritis prevents me from using it since day 1 totally.   How anyone able to use it on a Dobsonian is beyond my comprehension.  Can’t wait to see how it works out.   May be I should replace the red dot with a right angle finder for $80 instead?

 

 

So you have 6mm, 8mm, 16.5mm and 23mm.

You lack an eyepiece in between the 16.5mm and 8mm.  Beyond that is merely personal taste.

11mm would be ideal, but 10mm would be fine as well.  The best choice would be a 10mm Ethos.  With ultrawide fields,  the choices at 10-11mm are limited, but the 11mm Explore Scientific 82° is a possibility, or, if you could find one, the 11mm Tele Vue Type 6 Nagler.

If talking used eyepieces like the 11mm T6,  the ultimate is the Tele Vue Apollo 11, but a 10mm Ethos would be cheaper.

 

Edited May 28 by Don Pensack

[JOC]

4 hours ago, Don Pensack said:

So you have 6mm, 8mm, 16.5mm and 23mm.

You lack an eyepiece in between the 16.5mm and 8mm.  Beyond that is merely personal taste.

11mm would be ideal, but 10mm would be fine as well.  The best choice would be a 10mm Ethos.  With ultrawide fields,  the choices at 10-11mm are limited, but the 11mm Explore Scientific 82° is a possibility, or, if you could find one, the 11mm Tele Vue Type 6 Nagler.

If talking used eyepieces like the 11mm T6,  the ultimate is the Tele Vue Apollo 11, but a 10mm Ethos would be cheaper.

Don, how about a Baader Morpheus too, the 12.5mm would be almost in the middle of the gap, then they also do a 9mm or a 14mm.  They are fairly wide field, good eye relief and a little easier on the wallet!

I don't use the telescope a great deal, but do wear glasses and have the full Morpheus range, I haven't had any huge problems viewing through any of them with or without my glasses on.  FWIW unless you dealing with extreme astigmatism (and I deal with a modest amount) I often find no problem with taking my varifocal glasses off to view through the telescope, which after all contains a reasonable modicum of bits and bobs to focus any image to any viewer.

Edited May 28 by JOC

[Don Pensack]

To find the exact in between magnification, sum the magnification of the 8mm and 16.5mm, then divide by two.

Divide the focal length of the scope by that number to get the center focal length of eyepiece.

 

If you would prefer even % jumps between eyepieces, 23/1.4 = 16.43mm i.e.16.5mm.

Divide 16.5mm by 1.4 and you get 11.78mm, 

or around 11 or 12 to get the even jump in %.

 

Or, if you'd simply like a focal length in the middle, a 12-12.5mm would be fine.  And a Morpheus would be a good choice.

Edited May 28 by Don Pensack

[Legalpusher]

I have a 12” f4.9, 1500mm Dobsonian.

[Legalpusher]

Thanks for the advice.  I opted to buy the 12.5 Morpheus to fill the gap between 16.5 and 8.  It is a nice eyepiece at a reasonable cost.  It fills my need quite nicely.  I am quite pleased with the view and built quality. It has its own distinctive quality as compared to the Pentax and Tele-Vue eyepieces.

I am trying to decide if I should buy the 2x Powermate now, or save up for the 4.7mm or 3.7mm Ethos for planetary viewing.  Another option would be the 4.7 Williams Optic.  I heard it is just as good for half the price.  Please share your views.

[rl]

@Legalpusher; I'm not sure where you are located but I'd consider very carefully how often you can use a magnification north of *300 even with a 12" Newtonian. For our friends in Arizona or Colorado this is less of an issue but in the UK it's *200 or *250 tops being the norm whatever the scope. Even if the conditions and scope allow high magnification, sometimes your eyes won't. Floaters can detract from the view for more vintage observers.

Mind you, both the TV E4.7 and E3.7 are tremendous planetary eyepieces (if you don't need glasses) and I won't be selling mine any time soon...I sometimes use the 4.7 with a 14" dob (f/l 1600mm) on a good night but to be honest they see more use on smaller scopes. Both are brilliant on an 8" f/4.5.

Edited June 16 by rl

[Don Pensack]

On 15/06/2024 at 11:43, Legalpusher said:

Thanks for the advice.  I opted to buy the 12.5 Morpheus to fill the gap between 16.5 and 8.  It is a nice eyepiece at a reasonable cost.  It fills my need quite nicely.  I am quite pleased with the view and built quality. It has its own distinctive quality as compared to the Pentax and Tele-Vue eyepieces.

I am trying to decide if I should buy the 2x Powermate now, or save up for the 4.7mm or 3.7mm Ethos for planetary viewing.  Another option would be the 4.7 Williams Optic.  I heard it is just as good for half the price.  Please share your views.

If you are referring to the XWA 110° eyepiece, a few notes:

1. It's actually a 4.8mm focal length.

2. It's very sharp, even as low as f/4.

3. William Optics hasn't offered that eyepiece for many years.  Its top was hard to use and later versions of the eyepiece have had a better design of the eye lens end.

4. There are other brand names the 4.8mm is sold under.  Just search for "XWA eyepieces" to catch all the labels the eyepiece is sold under.  You can also find my 2024 Eyepiece Buyer's Guide on cloudynights.com on the Eyepieces Forum to see all the labels, including the factory house brand label, Sky Rover.

5.You could do a lot worse than the Ethos SX eyepieces.  They are even excellent planet eyepieces.

Edited June 17 by Don Pensack

[Bivanus]

Bit the bullet on a APM 3.5mm 110° ep - verry happy with it, still surprised at how bright it is even in my 80mm , expecting dimmer views.

Still looking for 11mm T6 Nag , 17mm T4 Nag and 22mm T4 Nag with the caveat that if I get the 22 that will also get me the 11 - as far as I red everywhere the 22 barlows very good.

[Louis D]

52 minutes ago, Bivanus said:

Still looking for 11mm T6 Nag , 17mm T4 Nag and 22mm T4 Nag with the caveat that if I get the 22 that will also get me the 11 - as far as I red everywhere the 22 barlows very good.

I can't stand my 17mm T4 Nag due to its very strong SAEP.  It makes taking in the entire FOV at once all but impossible.  Shadows flit all around once you get close enough to see the field stop.  I retired it in favor of my 17mm ES-92.  Your mileage may vary with the 17mm NT4, though.

[Bivanus]

@Louis Dmight be right , it's one of those cases of seing with one own's eye 😉 but after almost having a scratched cornea on a 16mm T6  I'll try to get by. 

[Louis D]

12 hours ago, Bivanus said:

@Louis Dmight be right , it's one of those cases of seing with one own's eye 😉 but after almost having a scratched cornea on a 16mm T6  I'll try to get by. 

If you back off a bit from the eye lens and give up some FOV, as with the Meade MWA 26mm, the SAEP is tolerable in the 17mm NT4.  It might also be better under truly dark skies where your iris can fully dilate and accommodate the errant exit pupil rays.

SAEP aside, the 17 Nag is a very nice eyepiece optically.  It's also the only Tele Vue eyepiece that focuses at the shoulder like many non-TV eyepieces.  This makes it nearly parfocal with the majority of my eyepieces. 

It is a solid chunk of metal and glass.  You don't realize just how dense it is until you go to pick it up.

[Don Pensack]

The 17mm T4, though, is the only Tele Vue eyepiece I've seen EOFB (edge of field brightening) in.

It's sharp enough and comfortable enough, and, with glasses, doesn't have any pupil acquisition sensitivity (one of the advantages of wearing glasses),

But I couldn't abide the EOFB, which the 17mm Ethos is free from.

[Louis D]

3 hours ago, Don Pensack said:

The 17mm T4, though, is the only Tele Vue eyepiece I've seen EOFB (edge of field brightening) in.

The 12mm NT4 has EOFB pretty severely.  It extends nearly to the center.  I swapped it with my 12mm ES-92 to confirm, and all of the gradient background glow went away.  I swapped the 12mm NT4 back in, and there it was again.  I then examined it more closely and realized only the very central region on axis was free of it.