Are cheap wide-view eyepieces kellners?

[overlord]

I got a cheapo 2" 32mm for my dobsonian a few years ago and i have to say my plossels are way better. everything not in the middle looks like a globular and that is annoying. it might show a lot but it's really only got an area in the middle which you can see clear so are these kellners or what?

[mental4astro]

Yes, they are Kellners. The problem is that they are not really suited to fast scopes. The GSO Superviews are a little better, actually a whole lot better for the price, but these too are better suited to slower scopes. I've got the 32mm Kellner, and the 30mm Superview, and my scopes are f/5 or faster, and the Kellner is poor in all of them, and the Superview is a better design, but not the best.

If you are after good wide field, low power eyepieces, sadly you'll need to spend some bucks. The best I've used, with a 68deg FOV and with no coma corrector in my fast scopes are the TMB Paragon (sadly discontinued) and the Astro Tech Titan Type II (same EP as the Paragon but rebadged and cheaper), and the Tel Vue Panoptics. The first two are much lighter than the Panoptics and cheaper too. Go wider FOV than 68deg. and coma is a serious issue in fast scopes and requires the use of coma correctors.

[Rod]

I used to use kellners but never again. Erfles give a wide field cheaply but i found the one i had lacked good coatings so the image always looked washed out. I like the baader hyperions on my 12 inch f5. Orion stratus I think is the same design. They are bulky and heavy but reasonably priced. They have a 68 degree field too. They come up secondhand regularly and I think andrews sells them.

Rod.

[mental4astro]

Hyperions and Stratus I've heard good raps on, but I haven't used them.

But be mindful, not all pricey wide-field EPs are good on fast scopes. The Orion Q70 range is one of them. Good eyepieces, but only in slow f/ratios (I've used one of these too)

[koputai]

I think you'll find that cheap wide ange EP's aren't Kellners, they tend to be modified Erfles or modified Konigs.

Kellners have an FOV of only around 45 degrees, about the same as a Plossl.

If you're interested in eyepieces, here's a great read:
http://www.howardastro.org/documents/evolution_of_eyepieces.pdf (http://www.howardastro.org/documents/evolution_of_eyepieces.pdf)

Cheers,
Jason.

[mental4astro]

Jason look at "Cooke 5 Lens", p 32, a Kellner variant, with the characteristics of the GSO Kellner, :question:.

Just being the Devil's advocate, :lol:.

[koputai]

Yeah Alex, I had condidered the Cooke 5-Lens, you may well be right. It is quite similar to the Kellner 2.

Cheers,
Jason.

[overlord]

Ah Thanks!

Yep. Sounds nice. :thumbsup:

[overlord]

This is a really nice monograph. I love the Herschellian eyepiece looking like a cut-off sphere. Herschell often used nice simple solutions, such as in his Herschellian pseudo-off axis reflector. I love Herschell

I might try and get the biggest Plossel possible. ahaa. I got no complains with the plossl