9x63 Roof Prism Binoculars for Astronomy ?

[John]

How well do the 9x63 roof prism design binoculars do for astronomy purposes ?

I've seen low cost ones (under £50) which I'm pretty sure won't be worth bothering with but I'm wondering how the mid-priced ones such as the Bresser Spezial-Jagd or the Inpro Nightfall ones might fare under the stars ?

A couple of specific questions come to mind:

- Are these designs full aperture or are they vignetted in some way like the lower cost 70mm Porros can be ?

- Some claim a true field of 5.5 degrees - is this likely ?

Thanks

[Peter Drew]

There's no design reason for roof prisms to be vignetted, mid to high priced versions should be expected to be full aperture. Similarly, a 5.5 degree true field should be obtainable with suitable eyepieces. The main difference potentially is the 3D effect which increases with the separation of the objectives, greater in Porros than roofs. Not much of an advantage for astro.    ?