1. ## Widest View Eyepiece

What size eyepiece will give me the widest view with a 120mm f/8 refractor? I will be using a 2" diagonal.

2. ## Re: Widest View Eyepiece

There is a site called Astronomy.tools that gives calculations for figuring all sorts of optical metrics.
I have it bookmarked for this very thing.

3. ## Re: Widest View Eyepiece

It would be whatever low power eyepiece that gives you an exit pupil the same size as your dark adapted eye.

4. ## Re: Widest View Eyepiece

Originally Posted by Gabby76
It would be whatever low power eyepiece that gives you an exit pupil the same size as your dark adapted eye.
Well that's the minimum magnification, but that's not necessarily the largest field of view.

The largest TFOV will be provided by any eyepiece whose field stop maximizes the 2" barrel. So something like a 21mm 100° or a 31mm 82° or a 41mm 68° or a 55mm Plossl. All of these will deliver exit pupils of various sizes (with the 55mm Plossl giving the largest exit pupil and lowest magnification), but the TFOV will be pretty close to identical across all of them.

5. ## Re: Widest View Eyepiece

Try this one: Tele Vue Optics: Calculator

- it is for the Televue range, but gives a great idea of what is possible. (-and note the widest true field is the 41mm Panoptic and the 55mm Plossl)

- Dean

6. ## Re: Widest View Eyepiece

Russel Optics makes some very good super plossl eyepieces. My 2" 56mm rocks. Give them a look.

7. ## Re: Widest View Eyepiece

Originally Posted by Leveye
Russel Optics makes some very good super plossl eyepieces. My 2" 56mm rocks. Give them a look.
No arguing there. It is a well made EP. But, it will not give you max AFV available in 2", because it has a field stop of ~40mm.

8. ## Re: Widest View Eyepiece

Originally Posted by refractordude
What size eyepiece will give me the widest view with a 120mm f/8 refractor? I will be using a 2" diagonal.
To get max apparent field of view for your (or any scope with 2" diagonal) you need EPs with field stop close to 46mm. A few examples are:

Orion Q70 38mm, ~70 deg FOV, 45.7mm field stop.
William Optics Swan 40mm, 72 deg FOV, 46mm field stop.
TeleVue Plossl 56mm, 50 deg FOV, 46mm field stop.
Baader Aspheric 36mm, 72 deg FOV, 45mm field stop (my favorite ).

Most of 82 deg glass pineapples come close to max AFV, but not quite yet. For example ES 82 deg 30mm has field stop of 43mm, which gives you about 87% coverage of max AFV.

9. ## Re: Widest View Eyepiece

The design criterion for the 41mm TV Panoptic was to give the maximum true field of view available in a 2" format. The 82 degree AFOV eyepieces have wider AFOV but not wider TFOV.

10. ## The Following User Says Thank You to not_Fritz_Argelander For This Useful Post:

j.gardavsky (02-07-2018)

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