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Equipment Discussions >> Eyepieces

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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Nikon NAV-10SW vs. Pentax 10 XW
      #5678742 - 02/14/13 03:09 AM

I am wondering how the Nikon NAV-10SW compares with the Pentax 10 XW. I prefer 65-72 FOV eyepieces over larger fields. Any side by side comparisons?
Any other contenders in that range (also weight wise)?

Looking forward to hear your opinions and experiences.

best regards
Chris


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Ava
sage


Reged: 11/30/11

Loc: Sweden
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5678766 - 02/14/13 04:39 AM

The 10mm Tele Vue Delos would be a serious contender. I find mine to be the best wide field eyepiece I have (in close competition with my 13mm Ethos). Reports indicate that performance of the Delos and Pentax XW eyepieces are very similar but some prefer the ergonomics of one over the other. In comparing the Delos to my CZJ 10mm ortho the only easily noticeable difference is that the CZJ has very slightly less scatter. I have no experience with the Nikon NAV-SWs.

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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5679169 - 02/14/13 10:56 AM

Hi Chris,

I've done side-by-side comparison of various 10mm eyepieces.

XW 10 v.s. NAV SW 10 is virtually a tie. Both are very good from f/4. As I mentioned before, Nikon NAV SW series has very little rectangular distortion, which results in visible AMD toward edge. Image is clean but size of image gets visibly smaller than on-axis. You can easily tell that double star gets tighter and tighter toward edge.

It puzzles me why Nikon decided to do so when they market NAV SW as astronomical eyepiece. I guess they hope that they could sell NAV SW to spotting scope users. I am not sure they are successful, though

In terms of color rendering, NAV SW has the whitest color when you observe the Moon among wide AFOV eyepieces that I've tried.



Tammy


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PeterWar
super member


Reged: 08/25/11

Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #5679192 - 02/14/13 11:07 AM

Wow Tammy, what an interesting side-by-side comparison! I'm interested to know how well did the Televue 10mm Delos perform against their contenders?

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Nuphy
sage
*****

Reged: 04/23/08

Loc: Newport News, VA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: PeterWar]
      #5679254 - 02/14/13 11:33 AM

Tammy, I would be interested to hear how the Tak-10U UW performs in comparison.

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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Nuphy]
      #5679388 - 02/14/13 12:47 PM

Why is the 12.5 in that picture? ;-)

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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5679422 - 02/14/13 01:03 PM

Having now used both head-to-head in 10mm and 7mm, I prefer the Pentax XWs across the board. The NAV-SWs have a cheesy loose screw up eyecup and suffer eyeball glint as bad as any eyepiece I've ever used. They are quality eyepieces other than that, but these are ills the Pentax lacks, and the Pentaxes are easier to get hold of and cheaper to boot.

I like the XWs much better than my Deloses, too.

- Jim

Edited by jrbarnett (02/14/13 01:06 PM)


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Stellarfire
Pooh-Bah


Reged: 07/10/11

Loc: Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: jrbarnett]
      #5679496 - 02/14/13 01:34 PM

Quote:

The NAV-SWs have a cheesy loose screw up eyecup and suffer eyeball glint as bad as any eyepiece I've ever used.

- Jim





I tried Nikon NAV 14mm SW and NAV 17.5mm SW pairs in the Baader Mark V binoviewer. I found that the very bulky eyecup design of the NAV-SW's causes annoying nose clearance problems to me, no matter how low or high I adjust the cups. Regarding nose-related eyecup comfort problems, the 14mm was worse, the 17.5mm is barely acceptable. Of course, the eyecup may me completely unscrewed if desired. But for binoviewing, I prefer eyepieces with eyecups (in particular soft rubber eyecups), which are helpful to hold the eyes well positioned and centered.

Speaking of widefield eyepieces, I feel very comfortable and happy with the bino-friendly TV Delos models, and also the terrific Docter UWA 12.5, as discussed elsewhere on this CN forum, is da bomb in the binoviewer.

Stephan

Edited by Stellarfire (02/15/13 05:50 AM)


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coutleef
Post Laureate
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Reged: 02/21/08

Loc: Saint-Donat, Quebec, Canada
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: jrbarnett]
      #5679529 - 02/14/13 01:46 PM

Quote:



I like the XWs much better than my Deloses, too.

- Jim




why do you prefer the pentax over yhe delos??


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: SteveG]
      #5679649 - 02/14/13 02:41 PM

Quote:

Why is the 12.5 in that picture? ;-)




Hi Steve,

If you look at 1.25" nosepiece of NAV HW 12.5 carefully, you find Nikon EiC-10 Barlow lens attached.
It is designed for HW 12.5 to make NAV HW 10mm

You can look at the full resolution photo.
http://www.pbase.com/tammyhomma/image/143754314/original.jpg

Tammy


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Tamiji Homma
Post Laureate
*****

Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Nuphy]
      #5679683 - 02/14/13 02:54 PM

Quote:

Wow Tammy, what an interesting side-by-side comparison! I'm interested to know how well did the Televue 10mm Delos perform against their contenders?




Quote:

Tammy, I would be interested to hear how the Tak-10U UW performs in comparison.




Hi Peter/Stephan,

I've posted short impression here before:
Takahashi UW Eyepieces


Tammy


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #5680169 - 02/14/13 08:30 PM

Hello all thank you for your feedback!

Tammy your picture is great for comparing the size and visual appearance of all contenders. That strange winged eyecup on the Nikon did not work for me on other eyepieces in the past and the optical issue you mention is a show stopper. My understanding is that this Nikon eyepiece came from the spotting scope side and was modified for astronomical use, that might explain your findings.

Jim thank you for your impressions, eyeball glint is an issue that I'd rather stay away from. So the Nikon is definitely a no go.

Looks like the Pentax 10 XW will be the next addition to my lineup.
The Delos does not please my eye and living in Japan the Pentax is cheaper to buy than the TeleVue.

best regards
Chris


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ausastronomerModerator
Carpal Tunnel
*****

Reged: 06/30/03

Loc: Kiama NSW (Australia)
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5680198 - 02/14/13 08:53 PM

Quote:

Looks like the Pentax 10 XW will be the next addition to my lineup.

best regards
Chris




Hi Chris,

The 10mm Pentax XW is one of the very best eyepieces money can buy, at any price. I am sure you will be very happy with it. Any differences with other premium eyepieces at this level are subtle at best and in many cases just personal preference, or brand loyalty. I haven't used any eyepiece in recent years; and I have used a lot, that would in any way make me inclined to sell my 5mm, 7mm and 10mm Pentax XW's, which I have owned for 10 years now.

Cheers,


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george golitzin
Carpal Tunnel
*****

Reged: 02/24/06

Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: ausastronomer]
      #5680658 - 02/15/13 03:54 AM

Quote:

Quote:

Looks like the Pentax 10 XW will be the next addition to my lineup.

best regards
Chris




Hi Chris,

The 10mm Pentax XW is one of the very best eyepieces money can buy, at any price. I am sure you will be very happy with it. Any differences with other premium eyepieces at this level are subtle at best and in many cases just personal preference, or brand loyalty. I haven't used any eyepiece in recent years; and I have used a lot, that would in any way make me inclined to sell my 5mm, 7mm and 10mm Pentax XW's, which I have owned for 10 years now.

Cheers,




I've had some differences with John over the years, but not on this issue--I'm in complete agreement. And you can add the 3.5mm XW to his list.

-Geo.


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Scott99
Carpal Tunnel
*****

Reged: 05/10/07

Loc: New England
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: jrbarnett]
      #5681245 - 02/15/13 11:42 AM

Quote:

Having now used both head-to-head in 10mm and 7mm, I prefer the Pentax XWs across the board. The NAV-SWs have a cheesy loose screw up eyecup and suffer eyeball glint as bad as any eyepiece I've ever used. They are quality eyepieces other than that, but these are ills the Pentax lacks, and the Pentaxes are easier to get hold of and cheaper to boot.

I like the XWs much better than my Deloses, too.

- Jim




oooh, I was going to keep quiet about it to not diss the Nikons, but I was thinking the same thing - forget the optical differences, I like the XW body much better than the Nikons. Nikon seems to have bungled the ergonomics part, the eyepieces have a bulky ring that bounces around loose.

The XW's are big & heavy, but they really hit a home run with the overall use-ability of it. (Except for the safety groove of course). You can precisely dial in the eyeguard position, which combines with a rubber outside for protection and grip-ability. For years Tele Vue and others just sort of "mailed it in" in terms of the eyeguard, they were never the correct height. Pentax realized how important the eyeguard & eye position are with long focal length ep's.

With the XW's Pentax brought the rugged "sport optics" mentality to astronomy, and combined it with coatings and glass on par with Zeiss.


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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #5681371 - 02/15/13 12:39 PM

Quote:

Quote:

Why is the 12.5 in that picture? ;-)




Hi Steve,

If you look at 1.25" nosepiece of NAV HW 12.5 carefully, you find Nikon EiC-10 Barlow lens attached.
It is designed for HW 12.5 to make NAV HW 10mm

You can look at the full resolution photo.
http://www.pbase.com/tammyhomma/image/143754314/original.jpg

Tammy




Ah - you got me on that one Tammy! BTW, I really enjoy your posts and great equipment pictures.


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Stellarfire
Pooh-Bah


Reged: 07/10/11

Loc: Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Scott99]
      #5681450 - 02/15/13 01:08 PM

The optical qualitiy of the Pentax XW line is undisputed. But it would be great if Pentax would consider bringing a modified XW version with slightly reduced shroud diameter, which would greatly enhance the binoviewer-friendliness.

TeleVue did the same with the Ethos 13mm: Narrowing the barrel diameter from 63.5mm (Version I) to 62mm (Version II) made it more binoviewer-friendly to users with ~62mm IPD.

Stephan


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Stellarfire
Pooh-Bah


Reged: 07/10/11

Loc: Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Scott99]
      #5681469 - 02/15/13 01:16 PM

Quote:

Nikon seems to have bungled the ergonomics part, the eyepieces have a bulky ring that bounces around loose.





Yes, the bulky and rattling eyecup of the Nikon NAV SW's is a bad joke.

Stephan


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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Stellarfire]
      #5681487 - 02/15/13 01:23 PM

Quote:

The optical qualitiy of the Pentax XW line is undisputed. But it would be great if Pentax would consider bringing a modified XW version with slightly reduced shroud diameter, which would greatly enhance the binoviewer-friendliness.

TeleVue did the same with the Ethos 13mm: Narrowing the barrel diameter from 63.5mm (Version I) to 62mm (Version II) made it more binoviewer-friendly to users with ~62mm IPD.

Stephan




If they do that, MrNutty (John), is gonna, well, to be truthful, he'll probably buy the whole set.....and may have to start wearing two eyepatches.....

I actually know people who DO bino with these.


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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: csrlice12]
      #5681935 - 02/15/13 04:46 PM

Just got the call, my Pentax 10XW is in!!

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gb_astro
sage


Reged: 01/01/08

Loc: Sydney, Australia
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: csrlice12]
      #5682101 - 02/15/13 06:15 PM

On the 10SW I found the winged eyecup one of the best things about it.
Faces differ and for me this design almost completely blocks external light.

gb.


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MRNUTTY
Carpal Tunnel
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Reged: 11/22/11

Loc: Mendon, MA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: csrlice12]
      #5682251 - 02/15/13 07:55 PM

I may have to invest in a smaller bulls eye on my back! :-)

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ebone
journeyman


Reged: 03/09/08

Loc: Brazil
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: gb_astro]
      #5683788 - 02/16/13 04:02 PM

Quote:

On the 10SW I found the winged eyecup one of the best things about it.
Faces differ and for me this design almost completely blocks external light.

gb.




+1 on NAV-SW design.
I consider the Nikon's winged eyecups first class.
Very effective and confortable. If you want it's super eazy to take off and put back.


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5685054 - 02/17/13 11:56 AM

Quote:

Tammy your picture is great for comparing the size and visual appearance of all contenders. That strange winged eyecup on the Nikon did not work for me on other eyepieces in the past and the optical issue you mention is a show stopper. My understanding is that this Nikon eyepiece came from the spotting scope side and was modified for astronomical use, that might explain your findings.




Hi Chris,

I did another side-by-side comparison (Nikon NAV SW 10, Pentax XW 10, and Televue Delos 10) with faster scope (f/4). It showed something I couldn't see before with slower non-flat field f/5.5, f/7, f/8 scope.

Overall, astronomical use, I think Delos 10 is the best among three. NAV SW 10 is best among three in lateral color toward edge. XW 10 shows visible weakness beyond last 10% of field at f/4, image is visibly softened comparing to the others.

By the way, SW may have heritage of spotting scope eyepiece but HW is very different from SW.

Tammy


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ausastronomerModerator
Carpal Tunnel
*****

Reged: 06/30/03

Loc: Kiama NSW (Australia)
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #5685941 - 02/17/13 08:53 PM

Hi Tammy,

Just curious what scope you used to conduct the testing at F4. I am thinking that the softening you saw in the 10mm Pentax XW in the outer 10% of the FOV could have something to do with the scope / eyepiece interaction.

I have used the 10mm Pentax at F4.2 in an 18" Obsession Ultracompact for the last 6 or 7 years, and do not see what you saw. However, I do use a paracorr type 1 in this scope which eliminates coma and effectively makes the scope an F4.8 scope, so that could explain the difference in what we are seeing also. In all my other scopes which are all F4.5 and longer newtonians, it gives my a perfectly sharp field right to the fieldstop.

Cheers


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: ausastronomer]
      #5686020 - 02/17/13 09:37 PM

Hi Tammy

Thank you for this report.
Did you use your Pentax f4 (Modified Petzval) refractor for the comparison?

Most of my visual instruments are f8 and longer, so the performance at fast focal ratios is not a big problem for me.
Which one do you consider the best performer in terms of on axis sharpness and contrast?

The HW from Nikon seems to be a new and design, but the price and the large FOV are not my cup of tea.

best regards
Chris


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ausastronomerModerator
Carpal Tunnel
*****

Reged: 06/30/03

Loc: Kiama NSW (Australia)
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5686041 - 02/17/13 09:49 PM

Hi Chris,

Sometimes theres a lot more involved here than just the F-ratio, which really only affects the steepness of the light cone entering the eyepiece. In a lot of eyepiece/scope combinations it's the interaction between things like the curvature of the focal plane of the eyepiece and the telescope, in addition to the focal length of the telescope.

For example a 20"/F4 newtonian will exhibit the same amount of field curvature as a 10"/F8 newtonian, because they both have the same focal length. The 20"/F4 will have a lot more coma than the 10"/F8.

People often make poor eyepiece choices concerning their F10 Schmidt Cassegrains, which usually have an F2 spherical primary. An F10 SCT will have about the same amount of field curvature as a 10"/F5 newtonian and more coma.

It really depends what aberration Tammy is seeing to cause the field to soften in the outer 10% of the 10mm Pentax XW. ie. Is it field curvature, is it off axis astigmatism, or is it coma from the scope, or the eyepiece?

Cheers


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: ausastronomer]
      #5686050 - 02/17/13 09:52 PM

Hi John

You have a valid point, this is why I asked about the scope he used for the comparison.

regards
Chris


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Stellarfire
Pooh-Bah


Reged: 07/10/11

Loc: Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: chboss]
      #5686456 - 02/18/13 05:38 AM

I think Tammy is referring to his new Pentax 100 SDUF II f/4, as presented by him in the Refractor Forum on 11/12/12 (OP #5566331).

Stephan


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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Stellarfire]
      #5686550 - 02/18/13 08:11 AM

Hi Stephan

That was my guess...

regards
Chris


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: ausastronomer]
      #5687305 - 02/18/13 04:54 PM

Quote:

Just curious what scope you used to conduct the testing at F4. I am thinking that the softening you saw in the 10mm Pentax XW in the outer 10% of the FOV could have something to do with the scope / eyepiece interaction.




Hi John,

The test was done with Pentax 100 SDUF II f/4, flat field imaging scope.

I could be witnessing DM curve of XW 10 shown below but since we don't have similar design parameter published by manufacturers to compare, it is just my wild guess

http://pentaxplus.jp/archives/tech/xo-xw/64.html

I do see better edge image quality in Delos 10 than XW 10 with the scope. I don't (can't) see the difference with TMB 92SS f/5.5, or slower. From f/7.5 on, XW 10 and Delos 10 look almost identical to me under night sky.

Tammy


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ausastronomerModerator
Carpal Tunnel
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Reged: 06/30/03

Loc: Kiama NSW (Australia)
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #5687686 - 02/18/13 08:07 PM

Hi Tammy,

I think your assumption is correct. The 10mm Pentax XW does have a touch of inherent -ve field curvature. This doesn't manifest in newtonians which have inherent mild +ve field curvature, but it could manifest when used in a flat field 4" F4 imaging scope, which only has a focal length of 16". I don't think this is likely to be a concern for the greater majority of visual observers, who wouldn't be using such a scope for visual work. It's a bit like saying the brakes on my new Ferrari work really well when I drive it on the bitumen, but they don't work very well when I drive it on the grass. How many people buy a Ferrari and drive it on the grass?

What do you think is causing the softening in the outer 10% of the 10mm Pentax XW, Field Curvature, Astigmatism or eyepiece Coma? My guess as I indicated above, is that it is slight -ve field curvature.

Cheers,


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guardone
member


Reged: 04/01/13

Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #6237793 - 12/06/13 05:29 PM

Quote:



I do see better edge image quality in Delos 10 than XW 10 with the scope. I don't (can't) see the difference with TMB 92SS f/5.5, or slower. From f/7.5 on, XW 10 and Delos 10 look almost identical to me under night sky.

Tammy




May I ask if also Nikon appears identical at slower ratio?

My request is that, because I need a "hi-end" eyepiece, but with 5 mm. focal lenght for use in a 105/735 triplet, usually for "general" use, but expecially for terrestrial and planetary / moon viewing.

Since Televue Delos does not have a 5 mm. I have to get a Nikon Nav Sw, or Pentax Xw, or Vixen Lvw - which performance may I expect with that f/7 scope with them?
Nikon Nav is a better choice over the others?

I have read the "trouble" with AMD at the edge (but from how much degrees?), but the "whiter" tone is a good thing, I hope the "sharpness" is also not less good than the contenders, at least on-axis...

Maybe at f/7 the AMD problem is less visible?

Please tell me what do You think about above eyepieces, thanks!


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Tamiji Homma
Post Laureate
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Reged: 02/24/07

Loc: California, USA
Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6237899 - 12/06/13 06:36 PM

Hi Guardone,

I think 5mm focal length eyepiece for 735mm focal length is too short for terrestrial viewing, 147x is too much power for terrestrial viewing.

I suggest somewhere 50x-70x max for daytime terrestrial viewing. If you like city scape with full of straight lines, Nikon NAV SW is a good choice.

Regarding edge performance, at f/7, I don't see difference. They are all good.

For planet and the Moon, I think that 5mm-ish is good. If you are looking for astronomical use, I would suggest either Delos 4.5 (if you need eye relief) or Ethos SX 4.7 (if you want big AFOV).

By the way,I had a few annoyances with Nikon SW 7 before. Reflection from eye to eye lens and back to eye caused what we call "glint." Strange thing is that I don't get the glint always but if I did, it was indeed very annoying.

However, SW 7 in binoviewer gave me the best Mars. Go figure!

Tammy


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guardone
member


Reged: 04/01/13

Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #6237993 - 12/06/13 07:26 PM

Hello, thanks for fast reply!

The long story, is that I like using telescope for everything, but I don't have money for everything...

Anyway, for a while I had the Televue Nagler Zoom 3-6 mm. - the purpose was to test the magnification for every object - I have found that for terrestrial view, the maximum usable magnification is from about 100x to 150x (Baader GO 7 and the Zoom at 6 and 5 position), it depends, so You are right, maybe is sometimes too much, but I have already a Pentax XF 8.5 mm. for "relaxed" daytime views.

Finally I found that a "general" use (both terrestrial and astronomical) requires an eyepiece, in my site with my telescope, with a focal lenght between 5 and 6 mm. - sure 4.5 would be ok for astronomical, but really too much for terrestrial.

But 5 mm. is usually ok as the higher magnification for daytime, and "interesting" for astronomy, not too "weak" as maybe would be 6 mm. - a balanced thing...

Anyway, since 4.5 is too much for terrestrial and 6 not right for night, here comes the 5 mm.

The big doubt is what eyepiece is better in the 5 mm. league, I could not imagine the real difference between Pentax XW and Nikon Nav, I think I understood the AMD problem but I don't know how much would be at f/7 (only close to the edge?), they will be so different, even considering RD?

I have found a used Nikon cheaper than a new Pentax Xw, so that's the question... Vixen Lvw was the contender because of price and remarkable general opinion, anyway should be clear that I want an eyepiece with a lot of comfort...


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238232 - 12/06/13 10:20 PM

I searched for various distortion examples and the curios thing, that is plenty of images of RD, apparently there are always three examples: no distortion, barrel distortion (positive), pincushion distortion (negative) - I have not found any example of AMD, so apart theory I really don't know how it can appear...

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guardone
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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238308 - 12/06/13 11:12 PM

Even more confusing: in some sources, it is the contrary, so RD becomes positive distortion, but anyway is RD = pincushion, while AMD becomes negative distortion, but anyway AMD = barrel - is that correct?

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guardone
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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238371 - 12/07/13 12:23 AM

But anyway, an eyepiece free of rectilinear distorsion, is also orthoscopic?

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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238384 - 12/07/13 12:35 AM

Agreed with Tammy on the color rendering and aberration difference between the Nikon and Pentax - it's visible and obvious and neatly overcame my ergonomic preference for the Pentax eyecups. I didn't encounter any particular eye glint problems, but that seems to vary a lot here.

The other factor should still be price and availability and here the Nikon really hasn't done so well in the US.


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: etsleds]
      #6238434 - 12/07/13 01:37 AM

Yes, but if I understood, Tammy prefers Pentax aberration style (AMD free, as same for Delos?), despite the better color rendition of Nikon.

I am still not sure how looks an eyepiece RD free but AMD aberrated - of course I hope that this aspect is small, with a good field free of every aberration...


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238448 - 12/07/13 02:00 AM

Hi Guardone,

I leave the accurate definition of distortion (RD, AMD, etc) to other experts.

Harry Siebert's page shows how the distortion looks like through eyepiece using graph paper.

http://www.siebertoptics.com/SiebertOptics-eyepiececomparisons.html

People often refer to Holger Merlitz's excellent explanation of geometry distortion here.
It is a good read.

http://www.holgermerlitz.de/globe/distortion.html

From my experience with various eyepieces, Nikon NAV SW and recent Meopta Zoom eyepiece
show very little RD comparing to other wide AFOV eyepiece.

Here is how I describe.

Imagine that you have 4 stars forming a shape, say perfect small square. AMD free (near zero)
eyepiece shows the (almost) same distance between 4 corners when you move around in the field.
However, the shape changes, distorted square.

RD free (near zero) eyepiece shows the largest square (area) at center, moving toward edge,
the more moving to the edge, the more its area shrinks but the shape remains the same, square, very little distortion in shape.
Double star on axis is wider separated, at the edge, distance between stars is shorter, so tighter double star.

You notice this if you have a reference to compare. We have very little straight lines (like on graph paper) to
reference to see this distortion at night. Some people claim they feel seasick if star field moves like one
in Holger's page. I don't feel that. I guess I am not following (ignoring) closely geometric field distortion (wave) when I sweep
star fields...

If you like to see something geometric share in orthoscopic, you would need to restricted AFOV small enough (< 60 degree, more like 40-ish degree). Narrower AFOV does not mean orthoscopic, though. For example, Zeiss Abbe Ortho II shows mildly negative RD, ")(" shape even though it says ortho. I am guessing that it is because designed to be well corrected to f/4. unlike original orthos.

So far, well AMD corrected eyepieces (example Televue) that I've tried show good edge performance.
I am not saying that Nikon NAV SW (RD corrected, instead of AMD) has bad edge performance, though.
It is very good.

I don't think you need to be that obsessive about RD/AMD.
Most reports somewhat exaggerated more than necessary about slight differences...

I've never had single eyepiece that I can't stand except ones don't come to focus to infinity
But those don't come to focus to infinity on one scope work wonderfully on other scopes.

Tammy


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238455 - 12/07/13 02:07 AM

Quote:

Yes, but if I understood, Tammy prefers Pentax aberration style (AMD free, as same for Delos?), despite the better color rendition of Nikon.





I couldn't see any difference between XW 10 and Delos 10 using TMB 130SS f/7.
At night, I only can tell by touching eyepiece, not by looking through eyepiece

I wouldn't judge a eyepiece just by single criteria (color rendering, field flatness, ...). There are so many things. I guess ergonomics often play bigger role than single optical characteristic.

Tammy


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: ebone]
      #6238519 - 12/07/13 05:02 AM

Quote:

Quote:

On the 10SW I found the winged eyecup one of the best things about it.
Faces differ and for me this design almost completely blocks external light.

gb.




+1 on NAV-SW design.
I consider the Nikon's winged eyecups first class.
Very effective and confortable. If you want it's super eazy to take off and put back.




Just when I thought that those who like wings won't speak up, thanks guys.

Best,


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #6238524 - 12/07/13 05:08 AM

Quote:

Hi Guardone,

I leave the accurate definition of distortion (RD, AMD, etc) to other experts.

Harry Siebert's page shows how the distortion looks like through eyepiece using graph paper.

http://www.siebertoptics.com/SiebertOptics-eyepiececomparisons.html

People often refer to Holger Merlitz's excellent explanation of geometry distortion here.
It is a good read.

http://www.holgermerlitz.de/globe/distortion.html

From my experience with various eyepieces, Nikon NAV SW and recent Meopta Zoom eyepiece
show very little RD comparing to other wide AFOV eyepiece.

Here is how I describe.

Imagine that you have 4 stars forming a shape, say perfect small square. AMD free (near zero)
eyepiece shows the (almost) same distance between 4 corners when you move around in the field.
However, the shape changes, distorted square.

RD free (near zero) eyepiece shows the largest square (area) at center, moving toward edge,
the more moving to the edge, the more its area shrinks but the shape remains the same, square, very little distortion in shape.
Double star on axis is wider separated, at the edge, distance between stars is shorter, so tighter double star.

You notice this if you have a reference to compare. We have very little straight lines (like on graph paper) to
reference to see this distortion at night. Some people claim they feel seasick if star field moves like one
in Holger's page. I don't feel that.
I guess I am not following (ignoring) closely geometric field distortion (wave) when I sweep
star fields...

If you like to see something geometric share in orthoscopic, you would need to restricted AFOV small enough (< 60 degree, more like 40-ish degree). Narrower AFOV does not mean orthoscopic, though. For example, Zeiss Abbe Ortho II shows mildly negative RD, ")(" shape even though it says ortho. I am guessing that it is because designed to be well corrected to f/4. unlike original orthos.

So far, well AMD corrected eyepieces (example Televue) that I've tried show good edge performance.
I am not saying that Nikon NAV SW (RD corrected, instead of AMD) has bad edge performance, though.
It is very good.

I don't think you need to be that obsessive about RD/AMD.
Most reports somewhat exaggerated more than necessary about slight differences...

I've never had single eyepiece that I can't stand except ones don't come to focus to infinity
But those don't come to focus to infinity on one scope work wonderfully on other scopes.

Tammy




Excellent post on RD/AMD, thanks.

Highlight - same thing here, no "seasick" effect.

Your evaluation on Delos leading the pack dovetails the findings on the French asto-magazine (Delos 10mm vs Pentax & Nikon).

Best,


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6238997 - 12/07/13 12:42 PM

Quote:

I searched for various distortion examples and the curios thing, that is plenty of images of RD, apparently there are always three examples: no distortion, barrel distortion (positive), pincushion distortion (negative) - I have not found any example of AMD, so apart theory I really don't know how it can appear...




Yes...not many want to touch this concept with pictures. However, use your imagination for a moment and thing of a perfect circle Moon in the FOV. If there is AMD and that AMD is positive and progressively getting larger as one moves towards the field stop, then the Moon will progressively become magnified as a part of it is positioned at the field stop and the other limb closer in towards the center. If you imagine a Moon where left hapf is one magnification and right hald gets progressively more magnified, geometrically you end up with a squat egg shape. But the AMD can really be anywhere I suppose, so what if the AMD only was in a small region say at the 50% point towards the field stop. If you positioned the Moon's center in the middle of that more magnified region, then more like a football shape. It really all depends on how the AMD is behaving in the eyepiece, progressive, just a discrete jump at one region, etc. Of course we don't know that because manufacturers do not let us know those specifics of their designs.


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guardone
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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: BillP]
      #6239080 - 12/07/13 01:21 PM

Hello all,
thanks for links, I already "discovered" them yesterday, while searching images.
As Tammy wrote, Nikon has AMD toward edge (still I am curious where approx. would be this sensation), but it is negative, since magnification decreases: so the above example of Moon is not good.
And anyway I can imagine a star, but not a graph paper example, which has this negative effect, without influencing rectilinear distortion: I guess that I must try the eyepiece anyway...


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6239209 - 12/07/13 02:22 PM

The primary result of negative AMD (lower magnification, the farther from center) will be that the field will appear to be like a globe with the closest part of the globe in the center.

Picture if you were sitting 8000 miles out in space. As a city rounded the edge of the planet, coming toward you, it would appear small, and it would appear to be moving very slowly from left to right.
When it was directly under you, it would appear to be much larger (4000 miles closer) and moving quite rapidly from left to right.
When it neared the edge of the planet, moving away from you, it would appear to shrink and slow down in its movement from left to right.

Now, to relate this to a field of view in the telescope:
--if you timed the passage of a star across the field, you would get a longer period of time, and a larger true field, than the apparent field would imply.
In this way, apparent field and true field relate directly only in the absence of distortion.
--double stars in the center of the field would appear to move closer together at the edge of the field as the effective magnification reduces.
--planets would distort into non-round shapes as they neared the edge and details on those planets would become harder to see as the effective magnification lowered.
--if you panned across the sky, the stars would appear to move toward you in the center of the field and away from you toward the edges, as if you were looking at stars on the surface of a globe. This has been referred to as "rolling ball distortion", or "kaleidoscope distortion", but it is disconcerting.

AMD is typically not a linear function, like coma, where it is twice as bad 30 degrees off axis as it is 15 degrees off axis. It is typically non-linear and grows larger toward the edge of the field.
When the field of view is larger, say, than about 40 degrees, a designer has the choice of eliminating rectilinear distortion (pincushion or barrel) and leaving in AMD, or eliminating AMD and leaving in RD, or reducing both partially.

Many companies choose, for astronomical eyepieces, to "cure" AMD and leave in RD. This will make straight lines appear to curve as they near the edge of the field, but they will stay in focus and be the same size.
Other companies choose, for daytime spotting scope or binoculars eyepieces, to "cure RD and leave in AMD. This will make straight lines stay straight as they approach the edge of the field, but they will change in size.

So it has something to do with your primary usage as to whether you prefer AMD or RD in your widefield eyepieces. Because it is possible to have an "orthoscopic" eyepiece (no distortion visible) if the apparent field is very narrow. But the curves of AMD and RD separate as the apparent field grows larger, so it is not possible to solve for both in ultrawide eyepieces.

People have their own preferences, but AMD is generally considered to be worse for astronomical observations--especially if you let the object drift across the field as you watch it.

The good news is that the human visual system seems to see up to 7% RD as non-distorted if that distortion appears quite a bit off axis. That allows a designer to make an eyepieces with no AMD and quite a bit of RD left in and still appear to be distortionless.

If the eyepiece is to be used in astronomy, and you DO look at things near the edge of the field, very low AMD will likely produce a better view.
If you don't care much about the edge, then it shouldn't matter.

Just remember that edge of field aberrations also show up in a telescope: coma, astigmatism, lateral chromatic aberration, field curvature. And these all influence what is seen at the edge. When you look at all these things together ganging up to make the edge of field star images really poor, it's a credit to the designers that we see as little aberration as we do.


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Starman1]
      #6239244 - 12/07/13 02:40 PM

Graphical specs on Pentax XW:
http://pentaxplus.jp/archives/tech/xo-xw/64.html
shows 10mm XW to have:
--very modest Petzval field curvature
--a fair amount of astigmatism as you near the edge (at top of graph, the divergence between tangential (meridional) and sagittal curves increase dramatically
--field curvature is negative, impacting the result depending on the type of scope.

Test of 10mm eyepieces, with wavefront and chromatic analyses:
http://www.cieletespace.fr/files/InstrumentTest/201306__6_oculaires_10mm.pdf


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guardone
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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Starman1]
      #6239298 - 12/07/13 03:19 PM

Hello Starman,
I have already seen Your sticky before, thanks.

I "used" this topic but I have in mind 5 mm. eyepiece, I have to choose between a Nikon Nav Sw or Pentax Xw, I have already a Pentax Xf 8.5, and I ignore which aberration is more present in this eyepiece.
I only hope that all those theoric descriptions are just emphasized, because I cannot figure how can a so expensive eyepiece, look as a "fish bowl"...


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6239338 - 12/07/13 03:42 PM

Bear in mind that these distortions may or may not influence your perceptions of an eyepiece.
If you view each object primarily in the center of the field, and contrast is good and there is little scattered light, then whether the edge of the field is distorted one way or another is moot.
But if your goal is a flat field with no astigmatism, good contrast, no scattered light, with stars little tiny pinpoints all the way to the edge, then you have very stringent standards that will be lived up to by very few eyepieces.
To get that in nearly any reflector, a coma corrector will be necessary.
To achieve that in any scope will require the eyepiece design to be anastigmatic, flat in field, have superior coatings and well-polished lenses.

We typically have an expression that goes like this (paraphrased):
widefield--inexpensive--excellent correction: pick any two.


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6239429 - 12/07/13 04:35 PM

Quote:

nd anyway I can imagine a star, but not a graph paper example, which has this negative effect, without influencing rectilinear distortion: I guess that I must try the eyepiece anyway...




I think so. I really can't say how you are going to response to AMD/RD. That's why I am trying various eyepieces myself. It is hard to understand by reading someone's explanation.

I noticed it when I was looking for it. When I enjoy the view, I don't think of it.

By the way, I've tried several 5mm-ish eyepieces (Pentax XW 5, XO 5.1, Nikon NAV SW 5, Televue Radian 5, Ethos SX 4.7, Tak LE 5, UW 5.7, Siebert 4.9/4.5, ...)

I come back to my favorite Tak LE 5. I am not saying it performs best but I like it because I feel most comfortable with it.

Tammy


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: Tamiji Homma]
      #6239464 - 12/07/13 04:51 PM

Quote:

I come back to my favorite Tak LE 5. I am not saying it performs best but I like it because I feel most comfortable with it.

Tammy




And that kind of criteria trumps any graph or chart.


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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: BillP]
      #6239481 - 12/07/13 05:05 PM

You got that right Bill!

What gets me, is when someone has a string of eyepieces, and then ask us all which ones they should keep and which they should sell - Excuse me???

Sorta like asking someone else which girl you should have:-) - There are some things that only We know best.

This thread is not about any of this, so I apologize, for the OT.

Thanks,
-Chuck


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guardone
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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: JustaBoy]
      #6240014 - 12/07/13 11:05 PM

I have anyway read the tests in the french pdf linked above, they wrote that Pentax Xw is more neutral than the Nikon - but apart some different things, I see the various lambda/xx results, and ask: it is really noticeable a visual difference, for example, from lambda/40 to lambda/80 ?

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Re: Nikon NAV-10SW vs. Pentax 10 XW new [Re: guardone]
      #6240175 - 12/08/13 02:18 AM

To help answer a related question to that, i.e., how noticeable is on-axis apparent performance difference between two EP's, here's a post about the subject by Alvin Huey, whose assessment on the Pentax XW vs. Delos vs. Ethos came out before the French pdf and got the same results - click here, where the Delos made it tops. He also posted a graph on the improvement seen using a "dinky" 6" APO (difference not noticeable) and the bigger 22" light buckets, couldn't find the post but it was something like this:



Best,


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