Nikon NAV17 HW

[clive milne]

Last weekend I had my first real observing session since acquiring this eyepiece a little while ago.

Whilst I didn't have an opportunity to really make a critical evaluation due to clouds, my first impression is that it is indeed a keeper.

Sharp as can be expected.
The eye relief is comfortable if you don't wear glasses (Andrew might like to comment on his impressions with glasses)
As for transmission and clarity, again I would state that the eyepiece met my expectations (my expectations are high). I suppose to lend some context, Stephan found the viewing experience through this eyepiece to be surprisingly good. For those that don't know Stephan's proclivity for high contrast eyepieces... looking through an an optical abomination (defined by having more than 4 air/glass surfaces) requires 3 hail mary's as penance.
Not only could he find no fault... he waxed lyrical in praise.

I guess that puts it in the highly recommended category.

[ausastronomer (John Bambury)]

Hi Clive,

I have only had positive feedback on the Nikon NAV HW eyepieces from people I respect in the USA. I haven't used one myself.

Of course at the price point of about $1,100 which does give you 2 focal lengths (17mm/14mm and 12.5mm/10mm) for your dollars, it should be outstanding.

I have used the similarly priced 12.5mm Docter Optics 84 degree eyepiece ($900 plus for a single focal length) and it is also exceptional. Probably the very best single eyepiece I have ever used. Certainly a 13mm ETHOS beater, which I own.

Cheers,
John B

[clive milne]

Hi John,

One further aspect of the observing experience I think is worth conveying is the flatness of the (apparent) field. I was never really conscious of this parameter until I started observing with a large binocular Newtonian.
Nagler type 4's are still to this day one of the best designs for use in binocular Newtonians, but... the positive field curvature is unmistakable.

The nav in comparison seem to project a star scape that is more natural in as much as it seems to be flat and at a distance of infinity. Also, the field stop simply disappears... or at least fades from being a significant detail.
This all adds up to the perception of standing at the edge of the abyss (as distinct from looking at a picture on your monitor)

I'm guessing that if there is a possibility of an incremental step closer to eyepiece perfection above the Nikon NAV17 HW, it will either be a subtle refinement of the art of opto-mechanics or a wholesale change in the way we access our senses... ie) fire wire port in the back of our heads.

In the mean time, I will just order another NAV.

caveat:
I have not compared the NAV side by side with a docter or ethos....

[gb_astro]

Clive just to clarify, you used the 17HW in a Newtonian?
And with or without a Paracorr?
Thanks,
gb.

[clive milne]

Yes, it was used in a 25" f5 without coma corrector.

Being aware that no eyepiece (other than the pretoria) corrects for coma, i understand the nature of the aberrations visibile off-axis. With respect to the Nav; if there was any contribution to the comatic plume inherent in to a Newtonian of f/d=5, it was in no way obvious.

I would have to inspect the field aberations of the NAV in an anastigimatic OTA to venture a judgement wrt its overall correction.

My gut feeling is that it is very good.

best
~c

[alocky (Andrew lockwood)]

Certainly echo Clive's endorsement of this eyepiece. We didn't get a great deal of clear sky that night, but before I pulled down the 25" we were able to get a look at NGC2070 and compare the 17mm type 4 Nagler and the Nikon monster. Obviously it would be fairer to compare the equivalent Ethos, but since I'm I spec wearer I don't have one of those. With the Ethos' I have used in the past I can't generally see the field stop, but the Nikon has slightly more eye-relief and I could.
Otherwise, the image was extremely well corrected and rather sharp. Definitely need to spend more time looking through it
Can't remember if I used it when I was tracking down ESO257-19 that night or not - would have been a good test to see if all those extra surfaces affected the light throughput...
Cheers,
Andrew.

[Astrorish (Rishi)]

Interesting, did you order it from Japan? If so, where may I ask? And did they speak English? Thanks.

[MikeyB (Michael)]

Kokusai Kohki stock the Nikon eyepieces. The proprietor, Barry Gooley, speaks perfect US english and is very friendly and helpful: About Kokusai Kohki in English

[clive milne]

Originally Posted by Astrorish

Interesting, did you order it from Japan? If so, where may I ask? And did they speak English? Thanks.

From here:
http://www.kkohki.com/English/kkohkiparts.html

All communication was in English.
I found the transaction to be as fast and trouble free as ordering from the best equipment dealers in the U.S. actually better in one respect, ironically in regards to communication.

I wouldn't hesitate to source Japanese astronomical equipment through Barry or recommend him to anyone looking to buy it directly.

[Astrorish (Rishi)]

Thanks Michael and Clive. I know of Barry and his company is always rated highly for communication and service by overseas buyers on the net. However his prices are a bit higher than other vendors in Japan. Eg someone here in the UK bought a HW from kyoei during a trip to Japan.

http://www.kyoei-osaka.jp/SHOP/98957/634377/list.html

Unfortunately he said the people at Kyoei didn't speak any English. I had heard of someone on Cloudynights buying one for even less on amazon Japan though I personally wouldn't take that risk.

[clive milne]

Here is a report of my second impressions of the Nikon NAV17HW (with a paracorr);
This time versus Ethos 17 & Nagler type 4, 17.

Scopes used were 16" lightbridge with a Suchting primary, 25" Obsession (OMI primary) and 28" f4.2 Webster with Kennedy mirror.

First up, there is so little to choose between these eyepieces that subjective opinion of an observer having a casual glance is as large as any real intrinsic performance difference between all three. That is not to discount the fact that there is a difference, just that they are subtle and somewhat subjective.

A note about the telescopes needs to be inserted here to lend some context.
The 16": At the eyepiece a (very) small amount of astigmatism was able to be discerned, but only by comparing star images through focus. I'm 99.9% sure that this is due to the way the secondary mirror was attached to the secondary hub using silicon adhesive (not enough gap to allow for thermal expansion/contraction) be that as it may, using the paracorr the star images were crisp right to the edge in both the Ethos and Nikon (I didn't try the type 4).
I picked a pair of stars right at the limit of resolution with a fairly substantial differential magnitude (at least 5m) and then progressively de-centred them in the FOV until I could no longer resolve them due to off axis aberations. With the Ethos, that point was reached a fraction less than half way to the edge of the field, with the Nikon it was slightly more than half. Both of them held up exceptionally well right up to the field stop. That is to say that while the Nikon passed this test a hair's breadth in front of the Ethos, the difference between them is practicably zero in the real world.
Next up I centred a rich star field (eta carina) and committed to memory a couple of stars amongst the nebula and also in the dark lane which were just at the limit of detection. If there was a difference between the NAV and the Nikon, I couldn't pick it.

A little later, Andrew had NGC 5139 centred in the 25" with the 17mm Nagler in the focuser. When I replaced the Nag with the Nikon, Andrew indicated that he actually thought the view through the Nagler was better. I didn't think there was really that much in it, but Andrew is a skilled observer so I find no reason to imply that his experience is anything but entirely valid. As Andrew wandered off to tend to his imaging rig, I spent a little more time critically comparing the Nag to the Nikon. I have to say that I found the opposite to Andrew and judged the Nikon to have a touch better transmission and correction. I am inclined to put this down to Andrew requiring glasses, so the eye relief inherent to the Nagler type 4 makes them a better performing design for him.

As for Barry's 28"Webster/Kennedy.... this is probably the subject for a different thread, but this was first light for the beast and there were one or two issues out of the box that need to be addressed before a fair analysis can reasonably be made.

regards,
~c

Oh, and one final post script... One significant difference between the Nikon and the Ethos: Whilst they have a similar shoulder to field stop distance, be aware that the Nikon's 2" barrel is quite a bit longer so if you place it into a paracorr or star diagonal, it is the bottom of the eyepiece (where the filter screws in) and not the shoulder step that determines where you reach focus.

caveat emptor

[alocky (Andrew lockwood)]

Morning Clive - pity you went to bed before the seeing improved!
I agree 100% with your asesssment - and I thought I'd made it fairly clear that I was not comfortable using either the Ethos or NAV with specs on - and to see darkness between the stars in the core of 5139 requires exceptionally tight stars on axis - which I can do with the Nag. So, my opinion was really that I can see better with my specs on - so other people who suffer from astigmatism note - neither the Ethos or the Nav are particularly friendly in this regard. To me it's a bit like comparing two competitive MotoGP bikes from this year, with one from 3 or 4 years ago by riding them to work at peak hour. I need at lot more time using these things to try and rank them in terms of perfomance/value.
cheers,
Andrew.

Don't even get me started on the contortions I had to go to with my face to see the field stop on those ridiculous 120 degree Explore Scientific things...
Anyway once I've sorted out some image processing I'll be having a nap.