Is there any use of AFOV over 68 deg on 1.25"?

[ismangil]

I've been reading up on eyepieces, and somewhere along the line seem to got the notion that for 1.25" focuser anything over 68 deg AFOV is wasted.

However of course I can buy 13mm Ethos which is 1.25" barrel.

I can't find the reference now, so is it true you don't need ultra wides for 1.25"?

[Chris H]

You don't need them but they are nice to have. For example a 1.25" 13mm Nagler or Ethos will show you more sky for the same magnification than a 13mm 68 degree field of view ep. What you often here/read is that wide fields of view are not necessary for high powers because planets and more distant/smaller DSO's will easily fit in a smaller field of view. Ultimately it's all down to personal taste, I however love the 100 degree view through my 8mm Ethos, I can see the whole moon at x150, star cluster particularly those in Auriga look great and for small objects I like to have a bit of sky framing them.

[ismangil]

Oh so the wider FOV still works then. I thought they wouldn't even show in the smaller focuser.

[Moonshane]

you don't really need ultrawides for anything as you can generally buy a longer focal length eyepiece (to a point anyway) that will give you enough field, or a shorter focal length scope that will give you more field. they are nice to use though and give a wow factor not felt with e.g. plossls. this has not worn out yet for me.

there are two points here to consider I feel (ignoring cost and weight) :

1) do you have a tracking mount? if not then wider fields help to retain the object in view for longer and you therefore should see more e.g. planetary detail.

2) the ultrawide high quality EPs like the Ethos are also superb in every other way - contrast, sharpness etc and therefore are not just wide field eyepieces but superb eyepieces.

I have a tracking mount for my main planetary scope and my preferred eyepieces are BGOs (40 degree field) for planets and my 6-3mm Nagler zoom (50 degree field) for moon and doubles.

I have a 13mm Ethos but more often than not only use this in my bigger dob.

[ismangil]

Exactly why I am interested in wide field eyepieces, higher mags to combat light pollution while still giving wider view as lower mags.

So good to know I can go as wide as I can afford (which is currently not the Ethos!)

I was thinking the 82 deg eyepieces seems attainable next year...

[Chris H]

The type 6 Naglers go from 13mm down to 2.5mm but be careful they have 12mm of eye relief which can feel a bit tight.

[Anweniel]

Bought the 7mm Axiom Lx at the sponsors knock down and the difference in the views from a standard plössl was jaw droppingly amazing, with a short FL scope its not hugely magnifying, enough to get some detail from jupiter and some DSO but scanning the sky with the eyecup looked fantastic, retracting the eyecup and it gave a feel like I was just swimming about amongst those star fields

[catburglar]

There are a couple of trade offs here:

The widest field stop available in a 1.25 inch eyepiece is around 27mm, and this places a limit on the maximum AFoV at a given focal length. So you can get a 24mm 68 degree AFoV eyepiece in a 1.25 inch barrel, but the longest focal length 82 degree eyepiece will be around 16 mm. So you can use the eyepieces, but you'll be limited to shorter focal length and therefore higher magnification.

The second trade off is that of image brightness or exit pupil. As eyepiece focal length reduces in a given scope, the magnification increases and the image brightness or exit pupil reduces. So contrast does increase, but the image may become too dim to be useful.

You probably need to find the sweet spot of image brightness and contrast that suits you, your local observing conditions and the things you want to observe. In my experience for most DSO's this range is an exit pupil between 4 and 1 mm, but if you've got low levels of light pollution you may gain from a bigger exit pupil.

[Moonshane]

excellent post catburglar!

[John]

The widest 1.25" I've come across was the KK Widescan III 20mm which delivered a whopping (for a 20mm 1.25") 84 degrees. Very nice in an F/10 scope but edges of the field of view got somewhat "messy" below F/7.

[ismangil]

That's it, the field stop limitation. Thanks for clearing that up.

[ismangil]

And now I've got the keywords, here is the complete rundown:

http://www.garyseronik.com/?q=node/117

[John]

And now I've got the keywords, here is the complete rundown:

Exploring Low-Power Limits | Gary Seronik.com

Thats an interesting article - thanks for the link

I've always tried to squeeze the maximum field of view from my eyepieces even when I was stuck with .965" ones

[Chris H]

I always use the Tele Vue Optics: Calculator gives you all the figures you need.

[ismangil]

I always use the Tele Vue Optics: Calculator gives you all the figures you need.

Yup, great resources. Makes it easy to see how poor you are

[Adz]

That was exactly my reasoning for getting a 24mm Panoptic and 13mm Nagler. I was only using 1.25 fittings and they gave great widest performance for their magnification. Fantastic light weight set-up, but the nag was a little close eye relief.