Binoculars-focusing

[Richard]

Given: binoculars are fully operational and properly focused and adjusted.

What is happening when I view a distant object through the binoculars and to compensate for that certain part of my field of vision which is obscured by the binos (between the barrels) I 'extend' my focus onto the distant object to make the obscured part 'disappear'?

Is it my brain canceling out the obscuration? Or is it my eyes increasing their focus?

I understand the eyes are such an integral part of the brain that a true depiction of the brain would include the eyes and optic nerves.

 

[Matthew]

? Trying to figure out what you are asking...

Binoculars will, when properly adjusted, give an image that is roughly the size of your pupils (depends on pupil dilation, focal length, ...). Basically, each eyeball gets an image pasted on it. Properly matched, that image and your pupil diameter will be the same and there isn't anything else in your field of view that needs to be filtered out.

edit: Here's the "exit pupil" explanation:

http://nikon.com/products/sportoptics/how_to/guide/binoculars/basic/basic_05.htm

 

[Richard]

Lenses clean - CHECK

Diopter - SET

Interpupillary Distance - SET

The image of each barrel is independent of the other. The two images slightly overlap. Where they overlap is the obscured area I mentioned. No matter how I adjust the binoculars there will be no change. The desired change will be only when my eye focuses further towards the objective lens does the obscured area 'disappear'.

This happens on every binocular I have used. My eyes check fine.

Is it my brain compensating or is it my eye making the correction?

 

[DJTorrente]

The image of each barrel is independent of the other. The two images slightly overlap. Where they overlap is the obscured area I mentioned.

Not quite following you here. Where the images overlap is where your brain perceives depth, because the overlapping images have offset foci.

 

[Matthew]

I'll have to dig out my binos and give it a try. It sounds like your eyes are focusing on the objective rather than the object (if that makes sense). Like you describe - you need to focus your eyes on infinity rather than 8" in front of your face. I don't think it's your brain compensating or not, I think it's your eyeballs (controlled by your brain) focusing on the wrong thing. Kind of like looking out the window and focusing on the glass rather than what's behind the glass. Try that, and force your eyes to focus back and forth on the surface of the window vs what's on the other side of the window. Is that what might be happening?

 

[Richard]

Yes, you got it. It takes only a short time to properly focus but it's annoying especially when viewing fast moving objects or hard to spot distant objects.

BTW: I have a semi-regular routine of changing eye focus on near, med distance, far distance objects and repeat. I like to think I'm exercising the occipital muscles. A good example is when driving a vehicle you focus on the gauges, the rear mirror, the oncoming traffic, way out front. Repeat.

 

[Richard]

Not quite following you here. Where the images overlap is where your brain perceives depth, because the overlapping images have offset foci.

If you mean stereoscopic vision I understand. However, it seems you are saying that the binos forces the viewer to adjust to the instrument. I suppose if I had a really big nose it would be a similar effect.

 

[Matthew]

Maybe try closing one eye, that might force the other eye to focus properly right away. That might speed up the adjustment process so that when you open the other eye they'll focus properly sooner - just a guess.

I really like my Nikons (I can't remember right now, but I think they are 10x50) - I use them mainly for stargazing ( quicker than setting up the telescope and very easy to see Jupiter's moons ) and basic outdoorsy natury things. For fast moving objects a smaller magnification and wider field of view might help you catch the action better.

Hold the binoculars away from you and pointed at something bright. Look at the exit pupil, you'll see the bright spot in the eyepiece. If it's round then you have good optics, if they are squared off then you have cheaper optics. The refractive index of the different types of glass will show this kind of effect.

edit: Here's an example:

http://g01.s.alicdn.com/kf/HTB1GWbyFVXXXXc7XpXXq6xXFXXXz/201460814/HTB1GWbyFVXXXXc7XpXXq6xXFXXXz.jpg