Bino AFOV

[Cec]

Hi all,
18 inch dob and dek bino's
I am sure somewhere this has been covered before, but with the release of the newer Wide angle eyepieces, a couple of questios arose as I am looking at purchasing some eyepieces.
Q1. I have a pair of 19mm pans which are great for me, I am looking at purchasing a pair of 11mm 82 degree AFOV, and possibly a pair of 6.7mm 82degree, am I waisting money?, will I see the full 82degree field or will this be back to equivalent of 68 degree.
Q2. Can a barlow be used with bibo's, if so where is it placed??
I don' wear glasses while viewing.
Thank you all in advance
Cec

[dannat (Daniel)]

Cec the Barlow can be used, usually called an optical corrector with binoviewers or OCA. Are u using one to reach focus at the moment in the dob? Most have to unless you have adjustable struts.

The problem of seeing the whole fov when binoviewers usually refers to field Stop of ep & prism size of the binoviewers, it should not pose so much of a problem for shorter f/lengths like you are talking about, however when your eyes are this close together it lessens the movement you have, so in practice you probably won't be able to view all the fov, I think 68 is the max when you are looking straight on thru the bin viewer, though it won't matter as this will lessen the poorer edges you see in cheaper ep's & e edges of the view will stay cleaner

[casstony]

Since the field stop of the shorter focal length eyepieces is smaller than the clear aperture of the binoviewer, you will have the full 82 degrees available, though long eye relief and a skinny eyepiece body makes it easier to physically position your eyes to take in the maximum AFOV.

I think using a barlow is better than using short focal length eyepieces since the slower light cone should give better illumination of the FOV. The barlow is placed in the focuser before the bino. A 2x barlow will give something like 3.5x magnification with the binoviewer due to the extended light path. The Antares 1.6x barlow should work well with the bino giving a magnification of perhaps 2.5x? (there's a formula for calculating this - i'll try to find it).

[Satchmo]

Cec

I have no problem using a large binocular with twin 13mm Nagler Type 6 eyepieces which have 12mm eye releif . I can see the whole 82 degree field edge nicely.

[casstony]

How to calculate actual magnification when a barlow light path is extended: http://www.astunit.com/tutorials/barlow.htm

If you happen to have a GSO 2x, the barlow element can be unscrewed and attached directly the 2" denk nosepiece or the threads on the 2"/1.25" adapter, giving a lesser magnification than when using the full barlow body before the bino.

Whether or not a particular barlow/bino combination works with available focuser travel is a matter for testing.

[Cec]

Hi all
Thanks for replies.
Yes I am using an optical corrector(came with the denk big easy kit).
A pair of 14mm Explore scientific are starting to look good as they are on special at present.
Thise combined with a barlow should be great and still have good eye relief.
Has anyone used the Explore scientific 82 dgree with a bino??.
Thanks
Cec

[casstony]

There's a few threads on cloudy nights about the ES 82 degree eyepieces - I've followed them closely to decide whether or not to get any. Seems the eye relief is a touch on the tight side and one guy specifically rejected a pair of the 14mm for bino use after trying them. It's going to vary from person to person though - I don't like the Nagler type 6 even for single eyepiece use, yet most seem to like them and Satchmo finds them comfortable in a bino. You can probably use your own preference for eye relief as a guide.