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PostPosted: Sat Feb 04, 2012 8:19 pm 
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Joined: Fri Feb 03, 2012 3:31 pm
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Location: Long Ditton, Surrey, UK
Thanks David, advice much appreciated.

I will probably be making my first investment in better quality eyepieces than the Plossils supplied with my scope at Astrofest next weekend.

Anyone attending?

The Williams Optics sound great but at £69 too good to be true? There must be a compromise somewhere. I remember looking at the Skywatcher budget range of LER eyepieces, between £20 - £30. I have yet to find a review that has something nice to say about them!

Here is a review of the Vixen NLV range (5mm):

http://www.astromart.com/articles/artic ... cle_id=634

This astronomer commented on the narrow FOV but found this insignificant for a number of reasons.

Not taking too much of your time, am I?

Regards, Umar


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PostPosted: Sat Feb 04, 2012 8:37 pm 
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Although your scope is a GoTo I am not clear as to whether it is motor driven or hand driven.
If it has a motor an apparent field of 45 degrees at 250x should be O.K.
The true field would be 11 arc minutes.
If no motor the field would be crossed in about 40 seconds of time.

I used Ortho eyepieces with only 40 degree fields or Kelners or Edmunds RKE with 48 degrees either driven or undriven scopes.
But I did not need glasses.

I have a Vixen similar to the oneyou are interested in but have not used it much.

There are so many eyepieces around nowadays.

You will probably get a special price deal at Astrofest.
I wonder if they would do two for one or three for two prices.

Try to find out if the Williams are good. I don't know.

Regards, David


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PostPosted: Sat Feb 04, 2012 9:04 pm 
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I read the test.

If there is no test of the Williams it may be best to choose the Vixen.

The main reason is that I think the Vixen is made in Japan?
Generally Japanese optics have much better quality control than do Chinese optics.
I presume the Williams is Chinese.

If I had an undriven Dobsonian 12 inch I would like to use extra wide field Naglers. But these are expensive and I don't know if a 6mm has enough eye relief for glasses.

So it is up to you to choose, maybe trying to find a test of the Williams. But if it is Chinese these vary because of not very good quality control in many cases.

Regards, David


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PostPosted: Sun Feb 05, 2012 5:19 pm 
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Joined: Fri Feb 03, 2012 3:31 pm
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Location: Long Ditton, Surrey, UK
Thanks again David.

Vixen also do LVW eyepieces - 55 FOV and 20 mm eye relief but not in 6mm, so maybe if I decide I need higher magnification, this is the best option? Half way between an NLV's field of view and a Nagler's, but much cheaper!

My skyliner dob is motorised and Astronomy now praised the tracking accuracy, so 45 degrees should be fine?

Do you think with experience, I could use such the narrow FOV eyepieces undriven?

If the above are 'yes' then the 6mm NLV should be my best option next week.

Thanks for the advice,

Regards, Umar


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PostPosted: Sun Feb 05, 2012 6:20 pm 
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Yes with experience you could track an eyepiece with only 11 arcminute field if the Dobsonian moves smoothly.
I used a 355mm f/5 altazimuth Newtonian and a 520mm f/3.9 Dobsonian by hand with similar fields.

The Meade UWA eyepieces are quite good with 82 degree fields. I am not sure of the eye relief.

55 degree fields are not really half way between 45 and 82 degree. But it is wider than 45 degrees.

I will look at the Meade UWA specs.

For a start I think the 6mm Vixen with the 45 degree field should be fine.

I presume you have a good finder if you use the scope without the motor.

You just put in a wide field eyepiece centre it and change to 250x.

regards, David


I mean a low power wide true field eyepiece, say 25mm eyepiece


Last edited by David Frydman on Sun Feb 05, 2012 10:18 pm, edited 1 time in total.

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PostPosted: Sun Feb 05, 2012 6:28 pm 
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The LVW Vixen are 65 degrees, so yes half way.

David


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PostPosted: Sun Feb 05, 2012 7:49 pm 
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The Meade 4.7mm series 5000 are I think good eyepieces with 82 degree field but only I think 13mm eye relief.
I don't think glasses wearers would see the whole field.
I am also not sure of availability although Rother Optics were advertising them.

David


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PostPosted: Sun Feb 05, 2012 9:26 pm 
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The 5mm Nagler has only about 12mm eye relief.
They make the Dioptrix that deals with astigmatism, but the whole cost is probably too great.
They even do the 100 degree eyepiece that takes these, but one of these plus a dioptrix probably costs as much as a fair sized telescope.

So the 65 degree Vixen eyepiece makes more sense.

Regards, David


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PostPosted: Mon Feb 06, 2012 10:14 am 
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Location: Lancashire
There is one area where very high powers have their use and that's for splitting close doubles.
Here we are only observing point sources, not extended objects with surface detail.

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brian


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PostPosted: Mon Feb 06, 2012 8:46 pm 
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Joined: Fri Feb 03, 2012 3:31 pm
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Location: Long Ditton, Surrey, UK
Is splitting close doubles the only viable use of very high magnifications?

I looked at Tele Vue's Nagler range, and coupled with a dioptrix they are well above my budget. It is still interesting that it is possible to correct astigmatism in that way. 

Is Tele Vue the only manufacturer of the Nagler design? Their LER radians appear to be cheaper than Vixen's LVW range, so maybe I should look at those in the future.

I just realised that I haven't researched zoom eyepieces or 2 inch  eyepieces. The variety can be overwhelming, but the NLV 6mm still looks favourable.

Much appreciated, Umar 


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PostPosted: Mon Feb 06, 2012 9:07 pm 
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2 inch eyepieces are only for low power wide fields.

Televues are very good. I hve not looked at Radians. Perhaps look at reviews.
I have used Naglers, excellent.

Very high powers I have used for testing fine optics, double stars, even unsplit elongated images of close doubles too close to split. Fine detail on Mars in exceptional Seeing.
Examining the discs of Jupiter's moons.

There is every reason to play with very high powers but mostly they are not as good as moderate or low powers.
Also the mount of the scope must be very good to use them.

Meade UWA series 5000 were I think chinese copies of Naglers more or less. They are very good, but Naglers are I think all parfocal or designed to the same high standards with the Dioptrx , I think not Dioptrix which I put earlier, available to fit most,

Televue have very high quality control although they sometimes sell cosmetically imperfect ones at U.S. swap meets.

regards, David


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PostPosted: Mon Feb 06, 2012 9:11 pm 
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Televue do two I think zoom planetary eyepieces but the field is narrow.
With a Dobsonian I would prefer a Nagler.
You have to look carefully at the eye relief as many Televues are less than 20mm eye relief.

David


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 Post subject:
PostPosted: Mon Feb 06, 2012 10:25 pm 
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Al Nagler, the designer and founder of Televue, of course has the patent on Televue scopes and eyepieces etc. Although some are designed nowadays by co workers.
So Naglers are only made by Televue unless they would licence some designs out, which i am not aware of.

The Chinese unfortunately pay scant attention to any copyrights, designs or anything. A few days ago The BBC 2 car programme pointed this out regarding to blatant copies of cars.
They make millions of other products that are just fakes.
But with Japanese or Western supervision or quality controllers they also produce excellent goods.
For instance most Skywatcher goods are high quality or at least very good value.
I have tried the Meade UWA and they were good, but they could be more variable than Televue.

Some of the cheaper Meade products are very down market, whereas Televue products are all high quality.

There is the 8 to 24mm zoom eyepiece which may have been originally Japanese and good.

The chinese cheaper copy has a much poorer reputation although it is good value.

As I said before we are spoilt by choice. When I started there was very little and scopes could take a year to be made. Now you get them the next day.

Regards, David


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 Post subject: Magnification
PostPosted: Tue Feb 07, 2012 9:46 pm 
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Joined: Sat Jun 21, 2008 11:32 am
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Location: se london
I use a 10" f6.3 unguided Dobsonian.
For planetary observation I have the choice of a 13mm Nagler, a 2x Teleview Barlow and a 8mm Vixen wide angle lanthanum.
For Jupiter and Saturn I generally find that the best and most comfortable view is obtained with the un-Barlowed Vixen with it's 20mm eye relief.
The only disadvantage I can see with the Vixen against the series 6 Nagler is it's about twice the weight which may cause balance problems.
To my eyes it,s image is every bit as good as the Nagler's but at less expense.

regards
Barry B


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 Post subject:
PostPosted: Tue Feb 07, 2012 10:17 pm 
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Dear Barry,
Thank you very much for that.
Which is heavier? The Vixen or the Nagler?
I used an early 7mm Nagler with the large undriven scopes and liked the fact that Jupiter was unchanged at the edge of the 82 degree field compared with the centre. The moons were also the same.
I did not like the 4.7mm? as there was almost nil eye relief. But I think the new designs are better.

I presume when you use the 13mm Nagler and 2x Televue barlow the focal length is 6.5mm so the true field will be about the same as the lower magnification 8mm Vixen, which I presume has a 65 degree field apparent, compared with the 82 degree apparent field of the Nagler.

I make it about 240x with the Nagler and barlow and 200x with the 8mm Vixen.
Have you ascertained whether the 8mm Vixen is actually 8mm or a little different?
I would think both Televue and Vixen focal lengths are pretty accurate.

With me I did not wear glasses, whereas with glasses the 20mm Vixen eye relief may be important.

Regards, David


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