With apologies to the late, great comedian....
I have never been a keen bino observer. Not that I haven't tried but here's how it is:
No matter what binos I have tried I always find difficulty in bringing both images together on the sky. In daylight, no problem at all although I have an old 8X40 Olympus pair that I had to perform some prism adjustment to to correct mis-collimation even in daylight.
My Bushnell 8X40 looked good from the get-go.
I have a Celestron Cometron 12X70 also good in daylight.
But at night on the sky, all three are unable to show an easy "single" image for me. I thought that, well, I just have an unlucky collection. All three just not good enough.
Then a friend let me use his brand new Nikon Acculon 10X50's.
At first blush these were much better than any of mine. Instant single image, perfect focus both eyes, nice color, no distortions.
I put up these, the Olympus and the Bushnells side by side and saw no difference! WTH? All were wonderful!
BUT...as I spent a few minutes comparing the three of them the old image separation effect appeared in all. Then I had to fight the seemingly spontaneous focus drift in both and different in each eye as well as constantly changing the IP distance for comfort.
By the end of this none of the views were any good.
There must be something wrong with my eye/brain connection to produce this. I returned to well lit room and tried again outside. Same result-good to start with but rapidly worsening as I guess my pupils open up.
It really does feel like my eyes are wandering uncontrollably. Sorry Igor.
Does anyone else suffer from this effect?
My eyesight otherwise is fine in monocular vision.