Wide Field Eyepiece

[vagk]

TV Panoptic 35mm or ES 30mm 82 for f/5 Dob ? (Without paracorr)

Someone who has compared them would help a lot

Edited April 20, 2022 by vagk

[Louis D]

Do you need to wear eyeglasses or not at the eyepiece due to astigmatism?  I prefer my 30mm APM over my 30mm ES-82 and 27mm Panoptic due to much better eye relief.  That, and the APM is sharp edge to edge at f/6 with no ring of fire like the ES-82.  The ES-82 gives a more immersive experience, but is tiring to use unless you pull back to the same field as the APM.

The 35mm TV Pan has been produced in two versions, one with a recessed eye lens, and one that's closer to flush mounted.  If you buy used, make sure to inquire which type it is.  Those who don't wear eyeglasses prefer recessed while those who do prefer flush mounted.  I've used the 35mm Pan at star parties, and find it very well corrected and usable with eyeglasses if flush mounted.

I prefer my 40mm Meade 5000 SWA or 40mm Pentax XW for widest field views.  At 35mm, my favorite is the discontinued Baader Scopos Extreme.  It is quite usable with eyeglasses and extremely sharp in the inner 60% of the field, and just barely falling off in sharpness to the edge.

[vagk]

9 minutes ago, Louis D said:

That, and the APM is sharp edge to edge at f/6 with no ring of fire like the ES-82.  The ES-82 gives a more immersive experience, but is tiring to use unless you pull back to the same field as the APM.

When you saying ES 82 gives a more immersive experience, you mean the biggest field it provides? The extra 10 degrees compared with APM, are not corrected well?

Edited April 20, 2022 by vagk

[Louis D]

In the 30mm ES-82, the outer 10% has CAEP, chromatic aberration of the exit pupil.  The red and blue ends of the spectrum focus above and below the average exit pupil distance.  The effect is to impart a color cast at the edge.  At night, you can't see it unless you move the moon or a planet out there.  A neutral colored planet like Jupiter splits into distinct red and blue images.  Each is fairly sharp, but they do not coincide in the field of view in my experience.  If you strictly keep objects centered and only look on axis, you will never notice this.  However, if you have an undriven mount and let objects drift from edge to edge, you will see it.

The field of view is very flat and sharp, it just has these slight issues at the outer part of the field.  That, and there is a bit of astigmatism out there, but it is relatively minor.

What's your budget and what are you hoping to view with any of these eyepieces and with what telescope?

[vagk]

I want an eyepiece which will provide me the biggest possible field of view for observing extended nebulas, open clusters, Andromeda galaxy etc. 

For example Pleiades

 

With ES 30mm, stars in the outer 10% will be a mess at f/5 without paracorr (dob 305mm 1500mm) ?

If so, I find the ES 82° purchase useless with the extra degrees being "faulty". 

Edited April 21, 2022 by vagk

[Louis D]

I would get the 40mm ES-68 if you want to absolutely maximize your possible true field of view.  It is the same optically as my 40mm Meade 5000 SWA.  There is just a bit of astigmatism in the outer field of view.  If you want absolute perfection, then the 41mm Panoptic is the way to go.  The difference in price is only $56 here in the US.

A lower cost alternative is the 40mm Pentax XW-R which has just a tiny bit more true field of view, a bit of field curvature (not visible to those with younger eyes that still focus properly), and a bit of edge astigmatism.  It's $120 cheaper than the 40mm ES-68 here in the US.  It's also considerably lighter.

Stars will be a mess in the outer 25% of the field of view without a coma corrector at f/5 regardless of eyepiece.  You would see a massive improvement with just the GSO/StellaLyra CC and a 25mm M48 spacer ring.  It's been good enough visually for me that I've not felt the need to get a Paracorr II.

It's much easier to take in a 68/70 degree field of view all at once than an 82+ degree presentation.  It's hard to appreciate what is going on in the periphery once you get past 70 degrees without looking directly at it.

At f/5, the exit pupil is going to be getting a bit large with a 40mm (40mm/5=8mm), so the sky will be somewhat washed out.  This isn't a bit deal with bright star clusters like the Pleiades, but the hazy nebula within it will be hard to detect.  You'd be better off with a smaller scope and smaller exit pupil to observe the dusty nebula around the stars to darken the sky background a bit.  You could always bump up to a 20mm to 30mm eyepiece in your f/5 scope to darken the sky background and observe parts of the dusty nebula in sequence rather than all at once.

At f/5, a 30mm eyepiece provides a 30mm/5=6mm exit pupil, which is much better, but still overly large.  The background sky will still be somewhat bright.  Personally, I prefer the somewhat washed out sky and easier to take in view of the 40mm eyepiece over the 30mm eyepiece.

Another option are the various 20mm 100 degree eyepieces out there.  There's the APM, Myriad, Astro Tech versions which are lighter, lower priced, and better performing than the ES-100 variant.  You lose some true field of view while massively darkening the sky (20mm/5=4mm exit pupil).  However, eye relief is tight and it is impossible to see the edge sharply without rotating your view way off axis.

There's no magic bullet here short of mounting a smaller scope to your f/5 scope for wider true fields of view.

Edited April 21, 2022 by Louis D

[vagk]

Thank you very much !!

[Don Pensack]

Louis pretty much summed it up.

At f/5, no coma corrector, narrower apparent fields mean less coma visible.

That leans toward a 68-70° eyepiece over anything wider.

Add a coma corrector, and the wider apparent fields will yield larger true fields at each power.

That leans toward an 82-100° eyepiece.

 

The Pleiades are a huge cluster of stars.  The best view is through telescopes that can yield a 3° field or more.

That is a wider true field than you will find in an 8-12" dob.

If you, for example, picked and eyepiece of 30mm/82° in a scope of 1200mm focal length, the field would be 43/1200 x 57.3 = 2.05°.

That's wide enough to capture the main 12-16 stars, but not all the stragglers.

Compare this image:

https://www.space.com/pleiades.html

with this image, to see what I mean:

https://en.wikipedia.org/wiki/Pleiades#/media/File:Pleiades_large.jpg

The Pleiades is truly a fantastic object for the 80mm refractor at 20x, but not great in a dob at low power.

 

However, that being said, if you're looking for the nebulosity around the stars, an 8-12" dob at around 100x, though it won't see the entire cluster in one field,

will show a lot of nebula and even details within the nebulosity.

Different horse for different courses, as the saying goes.

Edited April 21, 2022 by Don Pensack