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The Ethos - where do we go from here?


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Having been lucky enough to have had the opportunity to try some really good quality eyepieces recently of the standard, wide and ultra-wide field varieties I'm coming to the conclusion that the optical performance of the top brands is pretty constently excellent across the central 40-50 degree apparent field which is, as Steve says, the zone of critical vision.

With premium wide and ultra-wide eyepiece designs the observer has the option (budget allowing !) to frame that central zone with increasingly wider areas of well defined starry backdrops to suit a variety of tastes. There will be those that prefer the field stop to mark the end of the zone of critical vision and others (like myself) who prefer the frame to be a wide, sharp, starry background with the field stop only appearing at the edge of peripheral vision. We have a market at the moment which provides fine quality products, which address these varying preferences - which is great for us consumers :(

Therefore I don't think ultra-wide, sharp, eyepieces are intrinsically "better" than narrower field, sharp, eyepieces, they just cater for those of us who like their views served up that way. I recall when the TMB Monocentrics 1st hit the market with their 32 degree AFoV's, their advocates said that the narrow field of view was an advantage as it focussed the observers attention on the object being observed so that more subtle features and contrast would be more apparent. A plausible argument I felt at the time but eventually I found that I preferred the wider field views and that's the direction my eyepiece choices have gone. I can completely understand those that prefer a different type of view though.

I do feel that certain eyepiece designs have been "trendsetters" and have had a lasting impact on consumer demand and the eyepiece market (albeit sometimes through clever marketing as much as revolutionary design :)). The ones that spring to my mind are:

- Tele Vue Nagler - blending sharpness with ultra-wide fields.

- Vixen Lanthanum - comfortable eye relief combined with good sharpness and contrast and even, dare I say it, affordability.

- TMB Monocentric - re-igniting interest in simple, highly corrected, specialised eyepiece designs.

- Tele Vue Ethos - beating the Nagler at it's own game.

I'm sure that are a number of others that I've missed out :eek:

Getting back to Andrew's original question which I've interpreted as " what is the next big thing in eyepiece design ?", I've already mentioned zooms in my earlier post in this thread but I'm also wondering if modular designs might have interesting potential. What I mean by this is interchangable elements such as the eye and field lens groupings, spacers (like the Hyperion fine tuning rings) and even variable field stops (like the variable aperture on old 35mm slr lenses) so that you could mix and match to create eyepieces with the characteristics that YOU would like.

Anyway, thats enough eyepiece rambling for now I think :eek:

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I wonder if an image intensifier can be developed into an electronic eyepiece. This would give you watec/imaging views but without need for computers and monitors.

Sort of an astronomy version of night vision goggles. These products are available in the US (albeit with limitations) but cannot be exported as they are arms technology.

Clear skies

Mark

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Yes it "works" at that level ... but it cannot have more resolution than a fixed lens the same aperture could have.

And the level that it "works" at (for digital imaging) is rather dependent on having lots of computer power to process out the distortions etc (look up "point spread function" and "deconvolution") and/or masked by the lens assembly being matched to a tiny chip for low resolution imaging.

Dead right. In the past, people thought you could get beyond the diffraction limit by smart deconvolution. This has proven to be false for two related reasons:

  1. Deconvolution is a so-called inverse problem which is mathematically ill-posed. In practice this means that there is too little information to achieve a unique solution (correct image), or if there is a unique solution, it is highly unstable to small perturbation of the input. Perturbation of the input is unavoidable due to the photon noise.
  2. Information is actually missing because the aperture of the optics did not allow it to pass. It is this missing information which contains the fine detail, which therefore cannot be restored.

You can clean up diffraction rings which can cause ugly artefacts (especially in aperture synthesis radio telescopes), and you can sharpen a bit, by modulating the available information in the image, but you cannot create valid information out of nothing (that is called wild guessing :)).

There are situations in optical imaging when diffraction does not play a role: near-field scanning optical microscopy (NSOM). In this case light is completely reflected internally at the tip of a probe, but very close to the probe there is an "evanescent wave" of photons tunneling through the reflecting barrier. In this area the wave function of light is an exponential decay function, which has no physical wave behaviour (no sines and cosines appear in the equation), and therefore no diffraction pattern. It is possible to image individual fluorescent molecules with this system.

Unfortunately, our objects of interest are more than a few wavelengths away :(, so we cannot use a similar trick.

So to quote Scotty:

"Ye cannae break the laws of physics, Capt'n"

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These products are available in the US (albeit with limitations) but cannot be exported as they are arms technology.

For a start, they're close to CCTV - the detector is different because they work in long wavelength infrared - to see objects which are slightly warmer than their surroundings. The view of astronomical targets would be completely different to the optical view.

Secondly, commercial CCD detectors (for the visible wavelength range) are already extremely efficient. Amplification only yields more noise - an effect you must surely be familiar with if you've tried comparing an image with a digital camera taken at high ISO with noise reduction turned off compared with the same scene taken at low ISO.

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I sincerely hope that something much better than the Ethos will come along soon. Then I will be able to afford a second hand Ethos! You don't NEED the FOV but there is something delicous about feeling so emotionally involved, so 'lost in space.'

I would just love to try a monocentric though. I doubt they are of much interest to spectacle wearers but the purity of the design is so appealing. Dammit, maybe I'll just buy one, eh, and risk it? Trouble is, my favourite planetary scope is an f7 140/980 apo and I gather the monos really need more focal length than that. If I add a barlow I am adding glass and derfeating the object.

Olly

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What I've found with the Ethos is that it enables close up views AND still be able to fit larger asterisms in the single field of view. You get the object in it's context, not just looking through it (the 31mm Nag will let me see the Seven Sisters in a single field of view - gorgeous :))

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Andrew,

If I'm putting my Star Trek hat on, how about an eyepiece made out an adaptive material that would compensate for atmospheric distortion by deforming itself as you view?

Indeed maybe the whole concept of an eyepiece may disappear over the next 20 years - we will be star gazing on screens instead! Imaging and observing might converge. I think that's a long shot as there's something great about the thought of those photons travelling all the way across the universe to just to fall into your eye,

Cheers

Alan

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Having been lucky enough to have had the opportunity to try some really good quality eyepieces recently of the standard, wide and ultra-wide field varieties I'm coming to the conclusion that the optical performance of the top brands is pretty constently excellent across the central 40-50 degree apparent field which is, as Steve says, the zone of critical vision.

With premium wide and ultra-wide eyepiece designs the observer has the option (budget allowing !) to frame that central zone with increasingly wider areas of well defined starry backdrops to suit a variety of tastes. There will be those that prefer the field stop to mark the end of the zone of critical vision and others (like myself) who prefer the frame to be a wide, sharp, starry background with the field stop only appearing at the edge of peripheral vision. We have a market at the moment which provides fine quality products, which address these varying preferences - which is great for us consumers :(

Therefore I don't think ultra-wide, sharp, eyepieces are intrinsically "better" than narrower field, sharp, eyepieces, they just cater for those of us who like their views served up that way. I recall when the TMB Monocentrics 1st hit the market with their 32 degree AFoV's, their advocates said that the narrow field of view was an advantage as it focussed the observers attention on the object being observed so that more subtle features and contrast would be more apparent. A plausible argument I felt at the time but eventually I found that I preferred the wider field views and that's the direction my eyepiece choices have gone. I can completely understand those that prefer a different type of view though.

I do feel that certain eyepiece designs have been "trendsetters" and have had a lasting impact on consumer demand and the eyepiece market (albeit sometimes through clever marketing as much as revolutionary design :)). The ones that spring to my mind are:

- Tele Vue Nagler - blending sharpness with ultra-wide fields.

- Vixen Lanthanum - comfortable eye relief combined with good sharpness and contrast and even, dare I say it, affordability.

- TMB Monocentric - re-igniting interest in simple, highly corrected, specialised eyepiece designs.

- Tele Vue Ethos - beating the Nagler at it's own game.

I'm sure that are a number of others that I've missed out :eek:

Getting back to Andrew's original question which I've interpreted as " what is the next big thing in eyepiece design ?", I've already mentioned zooms in my earlier post in this thread but I'm also wondering if modular designs might have interesting potential. What I mean by this is interchangable elements such as the eye and field lens groupings, spacers (like the Hyperion fine tuning rings) and even variable field stops (like the variable aperture on old 35mm slr lenses) so that you could mix and match to create eyepieces with the characteristics that YOU would like.

Anyway, thats enough eyepiece rambling for now I think :D

You always put things across so well John. And always manage to find a middle ground setting up agruments for both sides....excellent post. :eek:

My own take is simple. There are dozens, perhaps 10s of dozens, of the same subject running on CN and Astromart. With back and forth arguments for all the eyepiece types. All the threads show one thing....there is such a huge variation in personal preference that the Ethos will not appeal to everyone and many will argue that there was no need for the Ethos let alone anything wider.

I agree with John, the zoom is perhaps the real area where some substantial advancements could still be made. The Speers zoom was the closest to offering what i really wanted. Which was a constant (or near constant) 80deg AFOV across it's range. Just a shame it was such a monster eyepiece and it didn't work with all scopes.

I love the idea of the Ethos, not used one, but would love too. I've really tried to embrace that agruement of the narrow field concentrating your attention on the subject at hand but for me it doesn't work. I just find the view restricted and the eyepiece uncomfortable to use. Had so many Orthos down the years because of their obvious value for money and bang for buck. But i always sell them happy to give up any tiny, almost undetectable, gain in light thoughput and on-axis sharpness, to use an eyepiece design with a wider AFOV and much more forgiving ER.

John's report of the Ethos just put a picture in my mind of what i really want from an eyepiece. I adore ultra wide views. There's nothing better (for me) than viewing an object at medium to high power but set in a wider field of view.

Russ

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I'm just curious: what's the largest aperture scope that anyone has ever actually looked through?

The biggest scope I have ever used was the 1.5 m infrared at the Arcetri Observatory in Gornergrat, Switzerland. Only used it for spectroscopy however, as it did not seem to have an eyepiece holder:p. Had to hand-correct the tracking as well (the Italian software left something to be desired:rolleyes:).

The biggest scope I looked through is the 16" RC on top of the building of my uni.

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You always put things across so well John. And always manage to find a middle ground setting up agruments for both sides....excellent post. :(

My own take is simple. There are dozens, perhaps 10s of dozens, of the same subject running on CN and Astromart. With back and forth arguments for all the eyepiece types. All the threads show one thing....there is such a huge variation in personal preference that the Ethos will not appeal to everyone and many will argue that there was no need for the Ethos let alone anything wider.

I agree with John, the zoom is perhaps the real area where some substantial advancements could still be made. The Speers zoom was the closest to offering what i really wanted. Which was a constant (or near constant) 80deg AFOV across it's range. Just a shame it was such a monster eyepiece and it didn't work with all scopes.

I love the idea of the Ethos, not used one, but would love too. I've really tried to embrace that agruement of the narrow field concentrating your attention on the subject at hand but for me it doesn't work. I just find the view restricted and the eyepiece uncomfortable to use. Had so many Orthos down the years because of their obvious value for money and bang for buck. But i always sell them happy to give up any tiny, almost undetectable, gain in light thoughput and on-axis sharpness, to use an eyepiece design with a wider AFOV and much more forgiving ER.

John's report of the Ethos just put a picture in my mind of what i really want from an eyepiece. I adore ultra wide views. There's nothing better (for me) than viewing an object at medium to high power but set in a wider field of view.

Russ

Russ, I entirely agree with you - John's post is spot on! In all other respects too - our views are very similar.

Might be interesting to make an UWA with an adjustable field stop - if you like a smaller FOV, just stop it down :)

In case there was any confusion - I never wished to imply that the Ethos is the be-all and end-all of eyepieces. I honestly do respect the fact that some do not get on with them and prefer smaller AFOVs. I was merely saying that the Ethos proves that huge AFOVs are possible if we so wish for it - AFOV is soon to no longer limit eyepiece design. Sorry to Steve and anyone else if that came across wrong :eek:

Thanks all for this great discussion!

Cheers

Andrew

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How about a quality wide-angle EP that has an Affordable Field Of View. :)

Sorry, its what I "read" every time I see AFOV.

Gets coat.

:(

I think that is happening, but rather slowly. The Skywatcher Nirvana's are now providing premium quality, ultra-wide views even in relatively fast scopes for a price that is significantly less than things like Naglers.

The other option is to own a slower scope of course - at F/10 most eyepieces work very nicely :eek:

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The other option is to own a slower scope of course - at F/10 most eyepieces work very nicely :(

True John, but I do fancy the idea of a truly wide field 'scope with reasonable light-grasp. Something like an 8" f/4 Newt.

Would wide-field EPs like the 55mm TV Plössl or the SW 38mm Panaview work well in such a fast 'scope?

Or would I have no option other than to pay the stratospheric, to me, price of a Nagler 31?

(I'm thinking in terms of widest tFoV, not necessarily the widest aFoV - though that could be nice. :))

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True John, but I do fancy the idea of a truly wide field 'scope with reasonable light-grasp. Something like an 8" f/4 Newt.

Would wide-field EPs like the 55mm TV Plössl or the SW 38mm Panaview work well in such a fast 'scope?

Or would I have no option other than to pay the stratospheric, to me, price of a Nagler 31?

(I'm thinking in terms of widest tFoV, not necessarily the widest aFoV - though that could be nice. :()

My understanding (some of it backed up by experience) is that long focal length eyepieces used in a fast scope create exit pupils which are too large in diameter for the average human eye to take in so some of the light is wasted. Plus you can experience problems such as seeing the shadow of the secondary, kidney beaning and blackouts.

Certainly in an F/5 or faster scope 30mm-ish seems to be the optimum focal length eyepiece - a fact that was very well known to Al Nagler of course when Tele Vue introduced the 31mm Nagler which delivers pretty much the widest possible apparent (and true) field of view in the 2" fitting. Of course other eyepieces are around that do that as well at much lower cost eg: the Moonfish 80 degree 30mm but what you are paying for in the more expensive 30mm class 2" ultra-wides is sharpness across the field of view at F/5 or faster. At least there are other options to the Nagler now eg: 28mm UWAN / Nirvana but I agree that they are still not exactly cheap :)

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Or would I have no option other than to pay the stratospheric, to me, price of a Nagler 31?

(I'm thinking in terms of widest tFoV, not necessarily the widest aFoV - though that could be nice. :))

Personally I greatly prefer the 35 Panoptic to the 31 Nagler. No black out zones, easier to use. My old WOLAS clubmates seemed to feel the same as I remember.

Olly

Oh, biggest scope yet used? 25 inch Newt at the public part of the Obseratoire d'Haute Provence. It was running on the Dumbbell. TBH quite similar to our own 20 inch. Progenitor star easily visible.

BEST scope yet used visually? TEC140.

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My old WOLAS clubmates seemed to feel the same as I remember.

Olly

Hi Olly, when were you in WOLAS? I used to try to go about 2yrs ago but haven't had much time lately. Big difference in the skies of West London (or Piggots) compared to rural France I guess.

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WOLAS? What a bird brain I am, I do apologize. I meant WPAOG - the Derbyshire group to which I belonged. I have had the pleasure of a couple of WOLAS visits to my place and just went dyslexic between WOLAS and WPAOG. Sorry. No one from WOLAS has ever said a word to me about the 31 Nagler! I'm a friend of Alan Longstaff's which is how I originally came to give a talk at WOLAS. A great club, I would say. Sorry to be so dim. And yes, the sky is just a tad better here than London or Derbyshire!!! (Not tonight though, honesty compels me to admit.)

Olly

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