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Old 02-08-2020, 07:17 AM
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Don Pensack
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Join Date: Aug 2006
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Quote:
Originally Posted by Stonius View Post
I know it's mostly to do with apparent FoV and eye relief, and it also depends upon the scope, BUT!


Are there any general consensuses? consensi? on the differences above and beyond that?


Current range with AFoV goes



Plossl (50)

DeLite (62)

Panoptic (68)

Delos (72)

Nagler (82)

Ethos (100)



Surely an Ethos isn't just a wider Nagler. Do they publish any data astigmatism, field curvature, aberrations and the like?


Would you for example, expect a Delos to have better on-axis performance than an Ethos? Are DeLites more for planetary observing like the Plossls?



Cheers


Markus
Some eyepiece measurements:
http://astro-talks.ru/forum/viewtopi...&t=1483#p41976
http://astro-talks.ru/forum/viewtopic.php?f=7&t=1897

I'll answer your questions directly:
1) Is there any general consensus on the differences above and beyond that?
The lines have different eye reliefs, important to many people, and the differences in apparent field are important in particular scopes, and different people prefer different eyepieces. TeleVue tries to make the feel identical across a line, but they only mostly succeed. Different focal lengths in a series always seem to get higher accolades. They differ in performance across a line as the above links show.
2) Surely an Ethos isn't just a wider Nagler. Do they publish any data astigmatism, field curvature, aberrations and the like?
No one publishes such data. Pentax did once a long time ago and the data is still available on the web wayback machine, but generally such information is proprietary and not released to the public. Lab tests to reveal the data you mention don't, by and large, exist in the astronomy market because the market is too small to pay for such tests and because most amateurs don't have the knowledge to interpret the results. not to mention that it might kill sales for a particular eyepiece if such data were known.
The Ethos is not a Nagler--it has more elements and different correction. It's a more sophisticated design, and possible only because of advancements in coatings.

3)Would you for example, expect a Delos to have better on-axis performance than an Ethos?
As I mentioned, eyepieces vary across a line. Not all Delos are equal. Not all Ethos are equal. However, the spot sizes for axial images say that any differences seen are likely to be due to seeing conditions. Everyone asks about on axis views, where the differences between eyepieces are minute. It is the edge of the field where the major differences between eyepieces exist.
4)Are DeLites more for planetary observing like the Plossls?
Plössls and Delites are general use eyepieces, not just for planets. Plössls, in particular, don't go to short focal lengths for planetary use because the eye reliefs get too tight. Delites were created to have vanishingly small spot sizes across the field and offer glasses-friendly eye relief to 3mm. They are TeleVue's "planetary" eyepieces if you prefer shorter focal lengths and narrower fields for planets. I favor the 3.7mm Ethos SX for Uranus and Neptune because the scope is a dob and at 500x, the objects drift across the field very fast. in my case, the Delite is too narrow for that. But they work fine in my 4" apo, which has a much shorter focal length.
But they work just fine as general deep sky use eyepieces in most telescopes. The 62° field of view works well for ease of use, and yields adequately large true fields in short focal length scopes.
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