Which bins are better

[Robby S]

I just bought 15x70 bins and have 30 days to return. Was wonder if I should upgrade to 20x80's or not. Is it worth It? I want to view DSO's. And wondering if it makes that much of a difference in what I can see with the bigger 20x80 bins rather than the 15x70 bins. Please help. Thanks! 

[Chris]

How dark are your skies where you are? Also, do you have a mount for them?

[Peter Drew]

15x70's can just about be hand held for a quick look, 20x80's need a mount. Either benefits enormously from being mounted. Assuming similar eyepiece characteristics the 15x70's should have a slightly wider FOV but the higher magnification and light grasp of the 20x80's should reveal better resolution of DSO's. Close call IMO.   

[Robby S]

33 minutes ago, Lockie said:

How dark are your skies where you are? Also, do you have a mount for them?

I live out in the country. Not totally dark skies but pretty dark skies. And yes I do have a tripod for the binoculars. Thanks.

[michael.h.f.wilkinson]

I prefer the 15x70s because I can just rush out to see something without the extra faff of a tripod. When I completed my Messier list, I spotted nearly half of the objects first with the 15x70s. I might replace them by 16x80 Opticrons or Vixen ARK (same bins, different badge), because that gives roughly the same FOV and some extra light grasp. I find 20x80 a bit narrow for some objects.

[Chris]

1 hour ago, Robby S said:

I live out in the country. Not totally dark skies but pretty dark skies. And yes I do have a tripod for the binoculars. Thanks.

Under pretty dark skies both the 15x70's and the 20x80's should perform well. They both have 4.6mm and 4mm exit pupils respectively (the size of the light cone entering the eyes), and this size of light cone should work well under dark skies. Under heavy light polution I try and keep my exit pupil around 2mm with my scopes when viewing DSO's.  

Having owned 50, 70, 80, 85, 110mm binos, I do feel the 15x70's are a real sweet spot for both the field of view, and that fact that you can lay back on a recliner and balance them on your eye sockets for hand held use. They also work very well on a monopod according to those in the know. 

I would keep the 15x70's for the convenience and field of view, then if you want to see DSO's more clearly, maybe use a telescope?  

It's also worth bearing in mind that if they are budget 15x70's they will no doubt have undersizwde prisms, so they would be more like 63mm, and the 20x80's would be more like 72mm.