Calling all nagler owners!

[asimov (John)]

Apparently they perform ok on a newt (F/3.5-F/8)..My concern would be what EPs are they compatible with, if their not naglers/pans/pentax etc etc. Will it get rid of the coma seen in a GS SV 30mm 2" for instance..In a few websites, they tell me this device was basically designed for nagler's & other high end EPs....but, and I quote 'the teleview paracorr works with other brands of EPs too' unquote. I have emailed certain companies requesting a LIST of the other brands of EPs the paracorr is supposedly 'compatible' with..

[Starkler (Geoff)]

A coma corrector such as a paracorr will not help an eyepiece which doesnt have proper field correction for a fast scope. Coma is inherent is fast newtonians and has nothing to do with the eyepiece itself. There are many who describe a poorly corrected eyepiece as suffering "coma", this is incorrect.

[asimov (John)]

Thanks for that tid-bit Geoff..To put it in laymans terms...Your saying not all eyepieces are 'corrected' to work in fast telescopes, their really designed for slow instruments. It's only since they've been producing fast scopes...mainly for amateur astronomers...that they realized they had to produce some 'corrected' EPs to overcome the coma created in a fast scope.(hence the invention of naglers/pentax & the like) So therefore, a paracorr would only work with EPs that have been specifically designed (corrected) to work in a fast scope.

I know this is the long version of what you just said, sorry about that.

One question: Are the meade 5000 series 'corrected' specifically for use in fast scopes?

[ausastronomer (John Bambury)]

Originally Posted by rumples riot

Incidently, only people who don't own TV EP's give them a less than perfect rap. Funny that. Wannabees.

That statement is about as vain as you can get, affording them isn't my problem, handling their short eye-relief with my glasses on is. Actually my wife's monthly credit card bill easily covers several of Uncle Al's finest. Several thousand observers throughout the Western World face the problem of needing eyepieces with longer eye-relief because of astigmatism.

I actually own a 27mm Pan and 2.5X powermate which I like a lot. The powermate is easily the best barlow I have used and I have used lots over many years. I previously owned a 16mm Nagler t2 and a 1.25" 1.8X TV barlow and they were both great products. The 26mm Nagler T5 is easily the best low power widefield eyepiece I have used, I prefer it over the 31mm because of the smaller exit pupil it creates in fast scopes. In the shorter focal lengths the Pentax XW's which are slighly superior to the older XL's are at least as good as anything Televue produces. They are both superb products, but I use the Pentax because of their longer eye-relief. Its a pity we all can't evaluate the performance of our equipment objectively instead of with a 1 sided approach and importantly consider all the factors that need to be considered when purchasing a $500 or more eyepiece.

In addition I suggest you take a look through a Zeiss orthoscopic if you want to see a sharp high light transmittance planetary eyepiece, somewhat superior to anything Televue has produced with a lot more neutral colour reproduction than some of Televues planetary eyepieces. But realistically they are at their best on a driven scope not a dob due to the narrow FOV. Come to think of it the 7mm Nikon ortho is almost as good as the Zeiss and somewhat superior to the TV offerings IMO.

CS-John B

[asimov (John)]

I keep getting drawn to these Meade series 5000 EPs... Just read a specific shoot-out...a nagler 5mm against the meade 5000 SWA 4.5mm. The nagler won out over-all....but not by much! The meade could by a very good option!

[mch62 (Mark)]

Just like to say that my choice of Naglers include all the long eye relief versions so I can use glasses or the dioptix corrector.
These are the 31mm Nag the 17mm Nag and the 12 mm Nag as well as 2 Radians for higher power which are all more than 17mm exit pupil distance.

You might have to choose these particular models if you whear specticals and the specifications are on the T.V. site .
I have still have orthoscopics and yes find them slightly better for planetary use but as you said eye relief is not user friendly.

The 31mm nagler will only give a 6.2mm exit pupil , in an f5 so is with-in the 5-7mm for a dark adapted eye, but this will depend on your particular pupil size .

[asimov (John)]

All the information I have obtained thus far from you guys has been great, & very informative. Apart from the odd over-looked question from yours truly, & some...shall we call them....un-called for comments.

[Starkler (Geoff)]

Originally Posted by asimov

All the information I have obtained thus far from you guys has been great, & very informative.

This is what we like to see at IceInSpace

& some...shall we call them....un-called for comments.

And this isnt what we like to see.

Some topics do have the potential to create heated arguments, but please do always keep differences in opinion civil and refrain from personal attacks.

For future reference, posts containing personal attacks are liable to be deleted.

[Starkler (Geoff)]

Originally Posted by asimov

Thanks for that tid-bit Geoff..To put it in laymans terms...Your saying not all eyepieces are 'corrected' to work in fast telescopes, their really designed for slow instruments. It's only since they've been producing fast scopes...mainly for amateur astronomers...that they realized they had to produce some 'corrected' EPs to overcome the coma created in a fast scope.(hence the invention of naglers/pentax & the like) So therefore, a paracorr would only work with EPs that have been specifically designed (corrected) to work in a fast scope.

Im not 100% sure from what you said that you understood what I was trying to say, so I'll rephrase.

Coma is a function of focal length only. As you get further away from the optical axis taking in a wide field view in a fast scope, coma can become an issue. Away from the optical axis, a parabolic mirror cannot focus to a perfect point and coma is the result. A coma corrector reduces this effect.

As for eyepieces, simple and cheap designs cannot handle the steep light cone from a fast scope and produce a sharp image across the field, resulting in abberations. This is not the same as coma.

So , a coma corrector wont make up for deficiencies in eyepieces.
I hope that helps.

[ausastronomer (John Bambury)]

John,

I will also try to re phrase what Geoff is correctly pointing out.

In newtonians Coma is an aberration caused directly by the parabolic mirror. It has nothing to do with the eyepiece and the eyepiece does not correct for it. Geoff correctly explains by saying it is caused by the angle of incidence becoming steeper as you go further from the central axis of the mirror, this causes a change in the lateral magnification at different points on the mirror. A good way to experience this is to focus the suns rays on concrete with a magnifying glass. When the magnifying glass is at 90% to the suns rays the light focuses to a point, angle the magnifying glass and the light focuses to a point with a fan-like tail, this is coma and what a paraccor is designed to correct.

A cheap eyepiece in a fast scope will suffer from numerous aberrations because the eyepiece is not properly corrected to work with such a steep light cone. These aberrations will mainly be astigmatism, field curvature and barrel and pincushion distortion. These aberrations will generally mask any actual coma that you would normally notice eminating from the fast parabolic mirror itself, as these eyepiece aberrations also get worse as you go off axis. A paraccor will not correct for these aberrations but it "may" clean them up a little, partially because the paraccor effectively increases the focal ratio of the scope by 15%. Another way to "clean up" the images when using cheap eyepieces in a fast scope is to use a longer focal length eyepiece with a decent barlow. ie a 30mm eyepiece with a 2X barlow will give a nicer image than a 15mm native eyepiece. This occurs because a normal barlow (2X) works by effectively doubling the focal length of the scope hence the focal ratio of the scope is also doubled. ie an f5 scope becomes an F10 scope when a 2X barlow is used.

A paraccor is not the answer with cheap eyepieces IMO, its expensive in its own right. If your going to use a paraccor you would generally do so with scopes faster than F4.7 or so and using good eyepieces so the paraccor is only correcting what its designed to correct and thats coma. Thats a personal thing however, as some use a paraccor even in an F5 or slower scopes, its up to the individual. I have no issues with coma in F5 scopes. I actually used an F3.8 scope (GOTH was his name) at SPSP without a paraccor and didn't find the coma intollerable.

I hope this explains it a little better for you.

CS-John B

Some topics do have the potential to create heated arguments, but please do always keep differences in opinion civil and refrain from personal attacks.

I think he is trying to point this out as well.

[asimov (John)]

Geoff & John B. Your lengthy, detailed explanations have certainly enlightened me a great deal, & I appreciate your time & efforts involved in responding to my questions. Even I find it hard to believe I've been into astronomy most of my life & yet know next to nothing about the technical side of it like you guys. But there is a reason for that, which I wont get into here.

I guess the moral of the story could perhaps be summed up as: For fast scopes, if you require optimum views you would be well advised to purchase 'up market' oculars rather than waste money on low budget ones..Would you agree with this statement?

[ballaratdragons (Ken)]

So, going by the above info, My f5 Dobbie actually becomes an f10 with my GS 2" 2x Barlow.

Interesting. I thought it just 2x magnified the image.

[janoskiss (Steve H)]

Tell me if I got this right now:

1. Parallel rays that are not parallel with the optical axis of the mirror are not focused to a single point. That kind of off-axis aberration is referred to as coma.

2. The other type of off-axis aberration associated with parabolic mirrors is that the image plane is not really a plane but a curved surface. The faster the scope the greater the curvature. That's the fast light-cone business, right?

3. Coma corrector like paracorr corrects #1, and top dollar eyepieces look after #2.

Am I even close?

BTW. It would be much easier to convey these things in diagrams. I myself was too lazy to produce any.

PS. do a google search for "light cone"!

[asimov (John)]

Ok. Although I would DEARLY love to own a nagler...My bank balance says 'please don't do it!?' So to keep the peace, I'm looking for definite opinions on these two oculars please.

1 televue plossl 11mm

2 meade series 5000 plossl 14mm

I would like to know A: How do these plossls rate, up against a nagler? According to reviews, the 5000 gives a nagler a run for it's money, & so does a TV plossl. (dont forget I run an F/5 newt)

B: If you were in my position & could not afford a nagler, would you purchase one of these 2 as a 'substitute' for a nagler?

C: If you had to choose just one of these out of the 2 mentioned, which one would you buy...& why? Their Both $145 each, just for the record.

Thankyou All for helping me out with excellent advise! Answer these 3 & I will be done, I promise!

[ausastronomer (John Bambury)]

John,

There are a number of eyepieces that work very well in fast scopes (down to F4) and provide superb image quality across the entire FOV that are reasonably priced. These eyepieces include Televue Plossls, University Optics High Definition orthoscopics and the Masuyama designs (5 element plossl) which include the Celestron Ultimas, Orion Ultrascopic, Antares Elite and Parks Gold Series. These are all the same eyepiece manufactured in the same factory in Japan with a different label on them.

I haven't used the Meade 5000 series so can't comment on it, but have used the Meade 4000 series and can only say that Meade don't exhibit the same quality control as the other manufacturers with their eyepieces. The early Meade 4000 plossls were made in Japan and were very good, the later Meade 4000 plossls were made in China and left something to be desired IMO. All of these eyepieces have 2 negatives, they have short eye-relief in the shorter focal lengths and they have a narrow AFOV, about 50 deg for the plossls and 45 deg for the HD orthos, the orthos have slightly longer eye relief than the plossls but its still tight, usually about 80% of the eyepieces focal length against 70 to 75% in the plossls. The image quality in these eyepieces is superb, as good as any premium eyepiece and clearly superior to what you would get in the cheaper eyepieces produced in China and Taiwan.

If you are working to a budget and don't wear glasses to observe these eyepieces are the best alternatives IMO, I think a 1st rate image across a narrower FOV is a lot better option than a poor image across a larger FOV.
The only thing you lose with these eyepieces compared to premiums like Naglers, Panoptics, Pentax and Vixen Lanthanum wides is the wider FOV and in the case of the Pentax and Vixen the comfort of 20mm of eye relief. Some Naglers and Panoptics have long eye-relief but only in the longer focal lengths and the Type 4's. In some cases the simple designs can provide a marginally superior planetary/lunar image compared to the premiums due to higher light transmission and more neutral colour reproduction due to them having less lens elements, although it usually takes an experienced observer to detect this. They are also usually smaller and lighter than the premiums hence their popularity for binoviewing.

If I was you, working to a budget using a tracking scope and also assuming you don't wear glasses ? I would buy either the Televue Plossls or the University Optics HD orthoscopics, or import the Antares Elite in from Canada. FWIW the HD orthos would probably cost you about $130, but they do have a marginally narrower FOV compared to a plossl. I prefer the orthos because of the high contrast and accurate neutral colour reproduction, but thats a very personal thing to suit my observing tastes.

CS-John B

[ving (David)]

Originally Posted by asimov

Ok. Although I would DEARLY love to own a nagler...My bank balance says 'please don't do it!?' So to keep the peace, I'm looking for definite opinions on these two oculars please.

1 televue plossl 11mm

I know its not a 11mm but I did a compario between a TV 10.5mm plossl and a 9.5mm GSO... yeah its not exactly a professional write up but feel free to read it anyhow

[asimov (John)]

I'd love to read it David...where can I find it?

[ving (David)]

er... BRB...

[ving (David)]

'ere ya go matey!
http://www.iceinspace.com.au/forum/s...10.5mm+televue