What’s the most transparent Tele Vue eyepiece?

[Novaload]

Quite a vague question really. Which Tele Vue eyepieces give the most transparent view and are there any particular sizes that are the most neutral? I’ve read that the Ethos 13mm and DeLite 5mm are particularly transparent.

Edited May 16, 2021 by Novaload

[rl]

If by "transparent" you mean "least light lost" then the Plossls would have to be in with a shout. Less glass is usually better in this respect. This assumes the coatings are the same as the more expensive offerings which may or may not be true. I'm guessing the shorter focal lengths in any given range would have thinner lenses which may convey a slight advantage. 

Having minimum glass in the eyepiece used to be big thing for many observers just to cut down the light lost, but modern glasses and coatings have made possible transmissions in complicated eyepieces which are not that far behind the minimum glass offerings, and future improvements will only make the gap smaller. But it's mathematically true that, for given glass types and coatings, the simpler design should transmit more light. 

Whether it's worth bothering about is a different matter. More basic considerations like magnification aberrations, and FOV would normally determine your eyepiece choice. It's probably more important comparing the same focal length from different manufacturers. Zeiss orthoscopics seem to have the best reputation in this regard.

A more relevant point might be what happens to the lost light. If you lose 5% of the light absorbed in the glass or scattered out of the field of view , that's not too bad. No-one will notice a 5% loss. if it comes back into the field of view as a ghost then it can be really very annoying. 

Edited May 16, 2021 by rl
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[Don Pensack]

rl is right.

A difference of 10% transmission in and eyepiece is a difference of 0.1 magnitude.

The average reflector loses 40% of its light at the edge of the field and very few can see it.

So transmission differences in eyepieces are not worth worrying about.

 

That doesn't mean that some eyepieces can't see deeper than others, but it doesn't seem to be related to transmission.

It does appear to be related to two main issues: spot side and lens polish.

 

Spot size is the focus of the eyepiece to bring a star image to a point.  If the spot size is less than the Airy disc size of the scope,

then the limit to resolution and sharpness will not be in the eyepiece, but in the scope..  This is the average situation, though many of us have found that the smaller the spot size the sharper the eyepiece,

so spot size becomes important in the smallness of details you can see.  Seeing conditions completely swamp this parameter, so we are talking about superb seeing conditions.

 

Lens polish determines things like light scatter in the field and around stars and basic contrast in the eyepiece, assuming coatings are excellent.  Superb polish and better contrast makes light transmission SEEM higher,

even if it isn't really.  And,  combination of the two qualities may allow you to see deeper.

 

[ Aside: Kellner eyepieces are notorious for internal reflections and ghosting, but I haven't seen a commercial Kellner with the high end coatings found in TeleVue eyepieces, which might let us know if it's the design or the execution.

Since they also aren't free of Chromatic aberration or lateral astigmatism, we're unlikely to see a high-end line of Kellners, though.  State of the art in 1849 is not the state of the art today. So coating technology plays a role in determining

light scatter, too.]

 

But, to answer your questions more directly, the Ethos, Delos, and Delite eyepieces were designed to be as color-neutral as possible.  The Plössl, Panoptic, and Nagler designs were not.

Note that that has nothing to do with spot size or lens polish, though the Delites are exemplary in both cases.  In my opinion, the Delites are TeleVue's "orthoscopic" eyepieces, in a sense.  Lunar/planetary observers have been asking

TeleVue for years to make a line of orthoscopic eyepieces.  They kind of did--it's just that they have long eye relief and 62° fields.  They aren't of course, actually orthoscopic, but then neither are most Orthoscopics.

People have their favorite focal lengths in every series, but keep in mind that telescope size, and type, and exit pupil, and seeing conditions, and personal preferences all enter into the picture.

One person may find a 27mm Panoptic perfect, yet another not like the eyepiece at all.

So there can be no "universal" answer to your question.  I've owned and used nearly every TeleVue eyepiece over the years, but my "favorite" has changed like the weather.  I could give you a list of my favorites since 1980,

but there have been almost as many as the number of years that have passed since then.  I have always favored the ones that yielded the tightest star images and the best contrast, though, which gets back to my point above.

 

[John]

Some observers in the USA who observe faint and far off objects with big scopes under dark skies came to the conclusion that the Zeiss ZAO orthos go the "deepest" followed by the Baader 10mm Classic Ortho, the 10mm Delos and the 10mm Ethos. All these eyepieces were deemed to be very good indeed and the differences slight, possibly only perceptible by the experienced observer with a big scope under dark skies observing challenging targets ?

Given the price of the Baader Classic Orthos it's quite a refreshing finding all the same

 

 

[Novaload]

Thanks for your help everyone.