The Ethos - where do we go from here?

[Andrew*]

Now that we have eyepieces that offer just about as much AFOV as our eyes can handle, which have fair eye relief, which have almost perfect light throughput, and otherwise practically optically perfect, where can we go?

Is there actually any room for improvement/development to be made in eyepieces?

[John]

Personally I wonder if the zoom eyepiece concept has room for further improvement. Al Nagler, Greg Speers, Baader and Pentax have shown that it's possible to deliver high performing zooms but each still has it's "quirks". A 5mm-30mm zoom providing 70 degree AFoV and 15mm+ eye relief across the range would be an awsome beast or even a set of two, eg: 4mm-12mm and 13mm-30mm would be great.

[michael.h.f.wilkinson]

I think the main gains to be made are through (even) better optical glass, with peculiar dispersion properties, allowing fewer lenses to do the same work. This will simplify production, lower price, and further reduce internal reflections etc. As we are seeing now, the lower-end EPs are improving, and they will continue to catch up with the Ethos and similar types.

Maybe active optics in the secondary mirror are the best way to improve matters seriously. After all, seeing is the main limitation to image quality.

[themos]

How about an eyepiece with a HUD, telling you what you are seeing, Terminator stylee.

[brianb]

How about something much simpler, with far fewer surfaces - for planetary work one simply doesn't need a wide field of view, the 20-25 degrees given by a monocentric is more than adequate, and there is, was and never will be a finer eyepiece for the purpose.

[michael.h.f.wilkinson]

How about something much simpler, with far fewer surfaces - for planetary work one simply doesn't need a wide field of view, the 20-25 degrees given by a monocentric is more than adequate, and there is, was and never will be a finer eyepiece for the purpose.

Apart from its eye relief?

[michael.h.f.wilkinson]

How about an eyepiece with a HUD, telling you what you are seeing, Terminator stylee.

That would completely ruin my observing experience

[brianb]

Apart from its eye relief?

The eye relief of a monocentric eyepiece is around 0.9f, greater than the orthoscopic (0.85f) or Plossl (0.8f).

[michael.h.f.wilkinson]

The eye relief of a monocentric eyepiece is around 0.9f, greater than the orthoscopic (0.85f) or Plossl (0.8f).

I know. But then I hate the latter two for their miserable eye relief at short FL. I did seriously consider the monocentrics, but the memories of banging my glasses against the old Plossl 9 and 10mm, and ortho 5mm I used to have were too bad for me to ever consider an eye relief below 15mm.

My old 0.96" 25mm Polarex ortho was another matter, that was a neat EP for the money.

[TheMightyKong]

Now that we have eyepieces that offer just about as much AFOV as our eyes can handle, which have fair eye relief, which have almost perfect light throughput, and otherwise practically optically perfect, where can we go?

Is there actually any room for improvement/development to be made in eyepieces?

Plenty! 100deg is actually much smaller than your eyes can handle, also personally I'd like better eye relief. Smaller would be nice.. could go on, I think there's always room for improvement:-)

[Steve]

How about something much simpler, with far fewer surfaces - for planetary work one simply doesn't need a wide field of view....

I agree with Brian. Astro kit is subject to fashion like just about everything else and the uber-wide eyepiece is currently in-Vogue. But, there are good arguments in favour of simpler designs that place all the available light in the 'optimum' field-of-view (the area that can be viewed without tilting our head to see the edges).

[H2IKXF]

Is there actually any room for improvement/development to be made in eyepieces?

Oh heavens above YES YES YES.

Why just a year or so ago I read an article about how Kodak, Canon or some other imaging company had developed a "lense" made of liquid. Where by applying a very small electric current the liquid could be made to change it's shape and thus magnify and focus.

Now this technology obviously won't work all that well for mirrors or objective lenses due to the issues of how the angle of the telescope is oriented and the effects of gravity on the liquid.

However, the above arguement doesn't really hold for eye pieces as in most cases they are at or very close to perpendicular to the ground.

That dew heater being used on the eye piece becomes redundant BUT the milliamps necessary to power that dew heater can now be used to operate the liquid lenses of the eye piece.

The possibilities for correcting whatever macular difficulties the viewer has along with possessing magnifications and resolutions approaching near infinity without the common lensing difficulties of glass are fantastic.

No... even if this technology doesn't work out in the end I will still say this:

If there's a will, there's a way. One of the best qualities of being human is the ability to find a way.

[brianb]

in most cases they (eye pieces) are at or very close to perpendicular to the ground.

Only when they're in the storage box.

magnifications and resolutions approaching near infinity without the common lensing difficulties of glass

The issue isn't the way the light is brought to a focus; it's the physics of light. You can't beat diffraction.

[H2IKXF]

Only when they're in the storage box.

Actually at that point they can be either perpendicular or parallel depending on how people put them in the storage cases. I'm soooo terribly sorry I did forget about all those people who use Dob's (among others) where the eye piece is precisely parallel to the ground when attached to the tube. My refractor's eye pieces sit at a 90° angle to the tube. When pointing the OTA at an object in the sky the eye piece is then "at or very close to perpendicular to the ground". Not exactly or precisely just "at or very close to".

But that wasn't the point of my statement. I was pointing out that the tech can't work on telescope objectives and mirrors due to the size involved and the angles. Gravity is too powerful for the amount of liquid (whether propelled/impelled by spinning or electrical current) to create a convex or concave shape and hold it. HOWEVER.... on smaller scales... like an eye piece it's possible for it to work.

The issue isn't the way the light is brought to a focus; it's the physics of light. You can't beat diffraction.

Don't tell me about how it won't work because it violates the laws of physics tell the inventors who've actually developed a working model and are now at the pre-production stages for incorporating this tech into the optics of camera's so people don't have to purchase so many different lenses.

[Andrew*]

Oh, excellent - just the kind of discussion I was hoping to kick off

Plenty! 100deg is actually much smaller than your eyes can handle, also personally I'd like better eye relief. Smaller would be nice.. could go on, I think there's always room for improvement:-)

I believe the eye has about 120° FOV, so the Ethos really isn't that far off the limit.

I agree with Brian. Astro kit is subject to fashion like just about everything else and the uber-wide eyepiece is currently in-Vogue. But, there are good arguments in favour of simpler designs that place all the available light in the 'optimum' field-of-view (the area that can be viewed without tilting our head to see the edges).

I think wider FOVs will always be fashionable from now on. Most people just don't like being restricted by small FOVs nowadays, and I don't think that trend will re-trace its steps. People trying larger FOV eyepieces almost always remark how it "sucks" you in, and intensifies the experience. We have 120° to play with , so why stick to less than 50°?

Simplicity of lens arrangements isn't the argument it once was due to modern coatings etc. All reports I know of place the Ethos very highly indeed in terms of sharpness, contrast and light throughput in anything less than perfect seeing. If eyepieces can do that with 10 elements, why do it with 4, except to cut costs?

I've been using my Zeiss orthos (arguably the best out there, and if not, comfortably second best after monocentrics) quite a bit recently, and always struggle to see any improvement over much inferior eyepieces (e.g. TMB/Burgess Planetary). Any improvements that can be made in terms of getting the last of planetary detail will be virtually impossible to discern.

Basically, what I'm trying to say is that we're pretty close to achieving the limit in AFOV and a whisker off achieving the limit in optical perfection. I think the main improvements will be made in cost (making optical improvements cheaper...), comfort (eye relief...) and ease of use (zoom function, size and weight...)

Active optics would be brilliant though - in my tests of the ZAO-IIs, seeing has mostly been the limiting factor...

All IMHO!

Andrew

[Steve]

I believe the eye has about 120° FOV, so the Ethos really isn't that far off the limit.

Yes, and some say even more, but that includes peripheral vision, not critical vision. If you look at one of the words in this sentence, how many letters either-side can you determine without moving your eye.... ?

[Andrew*]

Yes, and some say even more, but that includes peripheral vision, not critical vision. If you look at one of the words in this sentence, how many letters either-side can you determine without moving your eye.... ?

maybe 5, and at say one degree/letter, that would make 5° across! I wouldn't like an eyepiece giving a 5° FOV. We naturally move our eye to what we wish to view, and focus on a small area, and continue to move our eye around subconsciously to get detail from a larger area. In total our critical vision may use up the FOV of a monocentric, but not a lot of people having tried them would fail to wish for more FOV!

When we gaze up at night, without a telescope, we have a 120° FOV - isn't it wonderful? We can still appreciate the W of Casseiopeia, and seperate Mizar and Alcor, but we can flit from one area of the sky to another with minimal effort. Why should we not allow ourselves the same luxury at higher magnifications?

Andrew

[brianb]

Don't tell me about how it won't work because it violates the laws of physics tell the inventors who've actually developed a working model

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.

[Steve]

Andrew, I guess you are a fan of UWA eyepieces

[Andrew*]

I admit I am.

However, I have and use orthoscopics as well, so I am not necessarily "fixed" or overly biased - I just believe we're not using our eyes to the fullest by using them. For planets, true - we don't NEED more, but otherwise, why not...

Andrew

[brianb]

In total our critical vision may use up the FOV of a monocentric, but not a lot of people having tried them would fail to wish for more FOV!

For many purposes you're sort of right, but even 5 degrees is more than enough for planetary work when used with a scope with accurate pointing & tracking capabilities.

There is a real downside to all that glass, which is light absorbtion & scatter in the glass and from the surfaces. I've checked this carefully & found that a 20mm Nagler loses 20% light grasp compared with a 20mm Meade series 5000 Super Plossl in the same scope in the same conditions ... that's equivalent to a 10% aperture drop for using the more complex EP, and the Meade series 5000 is still a 5 element / 3 group design. Or, to put it another way, a 0.2 mag loss of limiting magnitude.

Personally I'm much more concerned about having that extra 0.2 mag of light grasp than the difference between a 60 deg field and an 80 deg field ... either is plenty wide enough even for deep sky work.

[Andrew*]

For many purposes you're sort of right, but even 5 degrees is more than enough for planetary work when used with a scope with accurate pointing & tracking capabilities.

There is a real downside to all that glass, which is light absorbtion & scatter in the glass and from the surfaces. I've checked this carefully & found that a 20mm Nagler loses 20% light grasp compared with a 20mm Meade series 5000 Super Plossl in the same scope in the same conditions ... that's equivalent to a 10% aperture drop for using the more complex EP, and the Meade series 5000 is still a 5 element / 3 group design. Or, to put it another way, a 0.2 mag loss of limiting magnitude.

Personally I'm much more concerned about having that extra 0.2 mag of light grasp than the difference between a 60 deg field and an 80 deg field ... either is plenty wide enough even for deep sky work.

This is very interesting. I have never heard this before. How is this calculated, and was it the Type 2 or 5 used in this example?

I wonder why this is not noted by people comparing e.g. Ethos EPs to those with far fewer elements? I remember recently Jahmanson made a comparison between an eyepiece/barlow combination comprising many elements with a single, simple eyepiece, and could find no difference in light throughput.

Andrew

[TheMightyKong]

Actually I think each eye's FOV is about 140-160deg horizontally and 130ish vertically. But you concentrate on a much smaller area, and pay less attention to the rest, I think that's why Naglers seemed so great till ethos, after which the old nags seem noticeably narrower. Personally doesn't bother me too much, depending on mood I'm happy at times with orthos.

[Steve]

Brian, is there room in that bunker for me

[brianb]

This is very interesting. I have never heard this before. How is this calculated, and was it the Type 2 or 5 used in this example?

Type 5.

Observed, not calculated. By checking the actual limiting magnitude against variable star charts, backed up by the ease in which objects just above the limiting magnitude were seen.