Telescope Reviews: Problem with new binoculars

What we refer to here as collimation, I will refer to as conditional alignment. You state that the images appear conditionally aligned, that is, star points appear to be merged between the two barrels.

The condition you have clearly described may come about if the images are brought into conditional alignment but the barrels are not aligned in mechanical axis or the lenses within the barrels are not aligned to the optical axis. In this case what may have been done is this.

Assume one of or both barrels or main objective lenses is not aligned to optical path.

Images appear not merged.

Collimation screws are then adjusted on one side to merge images. Conditional alignment of images is achieved.

Now one exit pupil has a distorted shape. It is no longer round, but appears oval.

What Is Wrong Here?

In order to achieve conditional alignment between two tubes where one or more elements in the optical path are not aligned with the optical axis and mechanical axis (other than a prism), the only available adjustment to the end user is to adjust a prism tilt screw. This will provide you with a merged image, a conditional alignment, but in effect may make a bad condition worse.

You may now have a binocular with elements not aligned with optical or mechanical axis AND tilted prisms. In effect this has changed the shape of the exit pupil. This is showing that the light path is off-axis in this barrel. But, it required tilting the light path to see a merged image. This was done by tilting a prism.

This is a perfect example of a situation where adjusting prism tilt screws can merge images but not correct an out of alignment optical axis. If something other than the prism was initially responsible for the images being NOT merged, and it required a large tilt of the prism to get a merged image, a conditional alignment, the condition will manifest itself by showing an oval exit pupil.

There are a number of conditions that may produce a similar result. It is possible that too much adjustment was made to one of the four prisms. It is possible that the wrong barrel was selected for prism adjustment. It is possible that the condition I describe above is the cause and no matter what you do you will not get rid of the oval exit pupil.

There are too many possiblities to figure which may be the cause.

You may need professional help to determine the cause. If you adjusted the prisms and created this situation, try to follow every step you took back to where it was before you did anything. Then procede with care taking note of every move you make. If this condition exists in a NEW binocular, contact the vendor.

Here is an article with a full discussion of the topic.
“Collimating” Binoculars

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