[astro744]

Originally Posted by Suzy

I'VE JUST COME ACROSS THIS...

The first thing to realise is that for the best in planetary viewing you need very different things to eyepieces used for DSOs (deep space objects), which is where the emphasis is placed on most general purpose eyepieces.

The primary difference is that eyepieces for DSOs are optimised for wide field viewing. To do this they tend to use large numbers of lenses in several groupings which inevitably introduces lateral colour, which is the death knell to seeing fine low-contrast details on the planets. The extra air-glass and glass-glass transitions also introduce more light scattering which causes a halo effect around bright objects. Again, this is not a problem for faint DSOs but a major issue for planetary viewing. The Nagler designs are often presented in a rather lazy manner as being the best eyepiece regardless of the question asked. In reality they perform particularly poorly in planetary use, in large part because of the sheer complexity and number of elements.

True planetary eyepieces are different beasts altogether. The primary job is viewing bright objects with as much detail and contrast as is possible. All other considerations are secondary. There is a strong advantage to minimising the number of elements even if this also reduces the field of view. True planetary eyepeices give much better light transmission, infinitely higher contrast and the absolute minimum scattered light. Space is black with a planetary eyepiece. It is often a murky grey with a wide field design.

For specifics, the Orthoscopic recommended by Andrew S would not be a bad choice but for my money I would go for a TMB Planetary II, which is around the same price but it has the edge even if it is fairly marginal. 5mm is probably about the right focal length. In a perfect world I would have said one of the TMB monocentrics, which really are no compromise planetary eyepeices, with absolutely unrivalled nothing-else-even-comes-close contrast. However, those are out of production now and as a highly specialised eyepiece they are unlikely to reappear on the market for the foreseeable future.
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Question: Will I get a better quality with the Pentax 60 fov, than the 68 fov. Also, the Pentax has 7 elements. Isn't that a lot? This guy is saying here the more fov, and more elements, the less quality. Waveytone in fact said the same thing regarding number of elements. I was hoping the Pentax would be different. I also have a dob, and that's going to be tricky with 60fov. I'm guessing I need to make a choice between being practical and quality.Oh golly, golly just when i thought I was making a decision.

Sorry guys for dragging this thread out for so long...It's just I don't ever intend to spend up like this ever again on an eyepiece. I'm trying to be the best informed before I buy.. thankyou for you help and patience.

Whatever applies to planets also applies to deep sky. If you are trying to see that very faint galaxy you are better off with an eyepiece with minimal glass elements, minimal scatter, sharpest on axis, minimal lateral colour and best light transmission otherwise you will not see the galaxy. For galaxies that you can see, such an eyepiece will give you a chance at seeing detail due to better contrast as a result.

Eyepiece design is a compromise and specialist eyepieces designed for planets will also work very well for deep sky. However, they will NOT have the eye relief you desire. They will NOT have the field of view you desire and they will cost more than $200 each.

Eyepieces offered today from companies such as Tele Vue and Pentax are multi-element designs that are needed to provide wide and sharp (both off axis and on axis) views. The glass and coatings used are the finest available and light transmission is only negligibly lower than a simple design if detecable at all.

If you are using an undriven DOB then you will NOT enjoy viewing with a narrow field, short eye relief eyepiece even if it does provide you with the best contrast.

I still recommend the Tele Vue Radian for the following reasons:

1. It is available in 5mm which you wanted.
2. It has a 60deg field of view which you also requested.
3. It has 20mm eye relief which is suitable for eyeglass wearers and is very comfortable for non eyeglass wearers.
4. It is sharp both on axis and off axis. If you ever have a chance to look through one you will see no distortion as a planets drifts from the centre to the edge and finally disappears from view. It is remarkable!
5. All Tele Vue eyepieces are designed to f4 and will work equally well at longer focal lengths.
6. You will get decent views of the band of Jupiter and Saturn with any quality eyepieces (not just a purist's planetary eyepiece) as you also requested.

As an alterative I would recommend the 5mm Nagler to give you the 82deg field that will allow you to view the object that much longer without nudging the telescope. However this eyepiece will cost a lot more than $200. The eye relief is fine for non eyeglass wearers.

I totally disagree with the comment about the Naglers being poor on planetary viewing. One of my best views of Jupiter and Saturn were through a 12mm T4 Nagler on a 10" f6 and 16" f5 telescope. In fact the view of Saturn through the 16" was 'Hubble' quality and you have to remember the eyepiece is but one part of the equation. To get a great view you need good primary optics, good eyepieces, good seeing and a good eye. The final image is only as good as the weakest link. Note I would like to point out that the 16" f5 has premium custom optics and a smaller than usual secondary.

I have never tried a 5mm XW Pentax but being a premium manufacturer I would expect it to perform well. Note neither eyepiece can be bought for $200 but a new Radian is close at $279 and perhaps can be found secondhand for near $200.

The monocentrics are for the purists and do perform well for the task they were designed for, both planetary and deep sky. I do not believe they are the eyepieces you seek or require for you needs and you will be jsut as happy if not more so with other premium eyepieces I have mentioned. Try and get to a star party/group observing session and try as many different eyepieces that are there on the night and you will then know better what you prefer.

Whatever you choose, enjoy!

Originally Posted by Wavytone

Hi Suzy, it seems you are learning fast.

First, I'll talk about eyepieces assuming you use your current dob, for which 5mm seems ideal for you for high power.

At high power,as you have realised, it's most likely you're looking at something small, on-axis, and a huge field of view is pointless assuming you can re-centre the object. What is more useful is the best image quality and contrast, on-axis.

it is for this reason many lunar and planetary observers are more interested in ep's with as few galss-air surfaces as possible, and would prefer MgF coatings (less scattered light when clean) to the broadband multicoatings (more durable but more scattered light).

The standout is the TMB supermonocentric (SMC) with just 2 glass-air surfaces.

From there its a toss-up between Brandons (best), Zeiss Abbe Orthoscopics (ZAO), Edmund RKE's (excellent bargain IMHO), or the run-of-the-mill ortho's which have 4 glass-air surfaces. Experienced planetary observers have some of these, if not a full set.

All of the widefield designs such as the GSO's, Vixen LVW's, Hyperions, Stratus', Naglers, Ethoi and the Pentax have many more glass-air surfaces and are all multicoated. Yes they give a lovely wide field, but look closely at a star or planet at high power and it's not such a beautiful view if you know what the textbooks say you should see with perfect optics.

Secondly there is the question of the focal ratio of your scope.

Trying to get good planetary images out of a typical f/5 dob is quite frankly fraught with the compromises associated with horribly short eyepieces.

If you want high power it is much better to start with a long focal length telescope (magnification = F/f, where F is the telescope focal length and f is the eyepiece focal length).

For example, for two scopes of the same aperture, one f/5 and the other at f/15, a 5mm eyepiece in the f/5 gives the same magnification as a 15mm in the f/15 scope. But the image quality will be chalk and cheese... an f/5 dob will have a huge secondary (degrades the image), and the 5mm eyepiece is a pain to use (never mind keep clean). An f/15 scope has a far smaller secondary (behaves like an APO refractor) and most 15mm eyepieces are quite comfortable to use.

Even better, almost all modern eyepieces work very well with an f/15 light cone, so there is really no need to splash out on the really expensive ones. On the other hand Brandons and orthos do not work well with scopes faster than f/7, usually they show some pretty horrendous aberrations over the outer third of the field of view.

It is for this reason I use an f/15 Mak, and a set of eyepieces that span 8 - 50mm...

* of the ones I mentioned, the Edmund RKE's were designed specifically for Newtonians at f/4,with respect to the curvature of the field and coma. For fast Newtonians these eyepieces are very much overlooked and they are startlingly good, for what they are.

What is the central obstruction of your f15 Mak? I would expect an f15 Mak to have a larger obstruction than an f15 Newtonian.

Originally Posted by Suzy

Could anyone please recommend a really good planetary eyepiece, 5mm, with good eye relief, neutral colour, over 50mm fov, and under $200.

I hear the wide fovs degrade contrast? And I know from experience putting a barlow on degrades quality somewhat, despite having a decent ED one. The 10mm I have at the moment isn't a good one (it came with the scope). Unless you'll can suggest a good 10mm that can handle a barlow ED well. Otherwise, I'll just use the 5mm straight. This will give me 240X on my 6" Dob.

I want to get decent views of the bands on Saturn and Jupiter. I was reading up on the TMB's but one review said it gives a warm and ruddy colour and you get better contrast by staying neutral. And as for the Orion Stratas, a review said there was flaring on the edges. And the Uni. orthos had a lack of eye relief and a small fov so were uncomfortable. I don't care what country I have to get this ep from, my invisible plane is ready to go.

This will be my last ep (yeah, you laugh!), so I want it to be a really good one.