APM 28x110

[dexter77]

Hello! Recently I've bought APM 28x110. Great giant binoculars. When I look on mountains and other terrestrial object everything is fine. Collimation is fine, objects are single and sharp. I can easily move hinges to adjust distance between eyes.

But I've noticed something else. When I look at night sky stars, sometimes collimation escape when I move hinges to adjust distance beetwen eyes. I see two stars etc. I need to try different position of hinges to set up collimation correctly. Why is it happening?

Is here anybody who also have APM 28x110?

 

Edited July 1, 2021 by dexter77

[michael.h.f.wilkinson]

Sounds like collimation is off. If collimation is not perfect, terrestrial targets can often be merged by the brain well enough, although eye strain can set in. With point sources, like stars, the brain equally accepts a double and a single star as valid results. Furthermore, there may be a situation that the collimation is conditionally correct, i.e. the two optical axes are parallel at a particular setting of the inter-pupillary distance (IPD). However, if both optical axes are not parallel to the hinge axis, they will lose collimation if the IPD is changed. This may be the case

[dexter77]

19 hours ago, michael.h.f.wilkinson said:

Sounds like collimation is off. If collimation is not perfect, terrestrial targets can often be merged by the brain well enough, although eye strain can set in. With point sources, like stars, the brain equally accepts a double and a single star as valid results. Furthermore, there may be a situation that the collimation is conditionally correct, i.e. the two optical axes are parallel at a particular setting of the inter-pupillary distance (IPD). However, if both optical axes are not parallel to the hinge axis, they will lose collimation if the IPD is changed. This may be the case

Ok, but how to explain that sometimes collimation is perfect and sometimes not? I'm not saying about view merged by brain. 
Like I said, it happens when you adjust distance between eyes.

When I set correct distance for my eyes sometimes collimation is perfect, but other day is not - I see two stars. I need to move back and forward IPD and suddenly fine collimation pops up.
Is here anybody here who also has this bino?

Edited July 1, 2021 by dexter77

[BinocularSky]

2 hours ago, dexter77 said:

Ok, but how to explain that sometimes collimation is perfect and sometimes not? I'm not saying about view merged by brain. 
Like I said, it happens when you adjust distance between eyes. More over, I've notice that after about 10 minutes bino is going to collimate itself well alone.

If your optical axes are not aligned with each other AND with the hinge, when you adjust the IPD, the angle between the optical axes will change. Your eyes detect this change, then adjust to merge the images. This strains your eye muscles and can result in headaches or nausea or both.

To see the effect for yourself, you need to fool your eyes into "thinking" that they are not looking at the same thing, so will not try to merge the images. Defocus one side so the image of a star is a blurry disc. You should see that the other star does not appear to be in the middle of it, and its position changes when you alter the IPD.

[dexter77]

Thanks to everyone for the answers.
Yesterday I had clear sky and free time to check it again.

So in my opinion there was a little wrong collimation on my IPD. My brain merged star to one, but when I close one and another eye I saw a liitle shift of the star (Altair).
It looked like this:

I've decideced to move a little bit a correct screw (number 4 on graphic, I was turning left to move star up/right) to achieve the same view in two lenses. It took me a 5 minutes to achieve good result.

Now, for my IPD the collimation is ok, but when I change IPD then binoculars are getting out of collimation - I see two stars. When I get back to my IPD and leave it - everything is fine.
So as someone said, maybe bino is "conditionally aligned"? I will try to send it to optical service in my country (Poland).

Edited July 1, 2021 by dexter77

[michael.h.f.wilkinson]

28 minutes ago, dexter77 said:

Thanks to everyone for the answers.
Yesterday I had clear sky and free time to check it again.

So in my opinion there was a little wrong collimation on my IPD. My brain merged star to one, but when I close one and another eye I saw a liitle shift of the star (Altair).
It looked like this:

I've decideced to move a little bit a correct screw (number 4 on graphic, I was turning left to move star up/right) to achieve the same view in two lenses. It took me a 5 minutes to achieve good result.

Now, for my IPD the collimation is ok, but when I change IPD then binoculars are getting out of collimation - I see two stars. When I get back to my IPD and leave it - everything is fine.
So as someone said, maybe bino is "conditionally aligned"? I will try to send it to optical service in my country (Poland).

You have indeed conditionally collimated the binoculars. Full collimation really requires a proper optical bench, lasers, etc, which is a bit beyond what you can find in your average garden shed

[dexter77]

Yeah, right, for my IPD is ok, but I will have to send it to optical service to get full collimation 

[dexter77]

Unfortunately in my country we don't have company that can make "true collimation" (lack of equipment), so I will have to use "conditionally aligned binoculars" or find some other way to fix it