2 inch eyepieces?

I have a TV 102 and a 10" dob that I use for telescoping. I have a reasonable 1.25 inch collection of EPs from 40 mm to 5 mm, which I am pretty happy with. Pentax and TV, Naglers/ Pans. I also have a single 2 inch TV 35 mm Panoptic, but it doesn't get used much since I have all those 1.25 inch eps.

I plan to get the 8 and 13 mm Ethos when I win the lotto, which is any day now.

Question 1: is the FOV the same using the 8/13 Ethos 1.25" versus 2" (what's the difference in use?)

Question 2: what other 2 inch ep would be a good fit between the 13 mm and 35 mm Panoptic? Or should I just get a Powermate and be done with it? Thoughts appreciated. Am stuck on this 2 inch EP thing...is it worth the $$ and hassle?

Thank.

Marc

Hi:

Here's a few thoughts:

- The FOV will be the same with the ETHOS regardless, it is the eyepiece's fieldstop that determines the field of view in this case.

- If you have a widefield eyepiece in the 24mm range, you are pretty much set.

- The field stop is a ring at the focal plane of the eyepiece. This is what you see as the edge of the field of view and it's diameter determines the AFov of the eyepiece. The maximum possible field stop diameter is determined by the Inner Diameter of the eyepiece barrel. In the case of a 1.25 inch eyepiece, this is about 28mm which means that maximum effective AFoV is only about 40degrees.

This is where that 35mm Panoptic becomes useful. With it's 68 degree AFoV it will provide a view that is about 50% wider, great for finding those elusive targets and many, myself included, enjoy the expansive bright views possible with such eyepieces.

jon

hi Marc, yes you must be the guy just behind me in the line to win lotto! I'm gonna spend mine on a custom 9" f9 apo

It's probably not what your bank account wants to hear, but the 13mm ethos really is something else. It's not just the field of view, it's the accessibility of that field. In other words there's no little eye hole to squint into, it's like looking through a window. Also as others have said, for a given true field of view the extra magnification darkens the sky and coupled with the excellent contrast of the ethos, the experience is breathtaking! They are big and bulky though, fine for a TV refractor but maybe more of a problem on a finely balanced dob.

My experience has been that I hardly ever need anything between my TMB 40mm and the Ethos 13. It sounds like a massive gap but the true FOV range isn't nearly as big as it sounds. 2.7° to 1.4° in my scope so it's like having a 20mm of the same design as your 40.

all the best

Tim

Marc Whitsett said:

Question 2: what other 2 inch ep would be a good fit between the 13 mm and 35 mm Panoptic? Or should I just get a Powermate and be done with it? Thoughts appreciated.

One thing to take into account is your age=max. size of dilated pupil.
I am thinking right now what to get above the 13mm Ethos. (scopes 16f4.7, 6f5 and 110f7)
I presume my pupil will be around 5mm by now.
So anything above 22-26 mm will give me an exit pupil greater than mine. Does it matter ? Here possibly opinions could split: maybe the visual field will be more important to you despite effectively looking through a "smaller" scope with such eyepiece ?
In my case, I have hard time to decide between Nagler 22 and Nagler 26. The latter gives me bigger than my pupil on the fast scopes I have.
http://www.klhess.com/telecalc.htm is a nice calculation tool for these deliberations.