I’m amazed the general user population hasn’t figured this out yet. Binoculars are a more complex optical instrument than a telescope simply because there are two optical paths with more optical surfaces that must by critically aligned.
edited 11-26-02
If images are not aligned, but you are starting with nice round exit pupils, you can tilt the prisms to merge the out-of-collimation images, but you might then be moving the prisms out of alignment.
True collimation is the aligning of all the optical elements along the binocular optical axis. No optical element should be tilted from the optical axis.
I must admit that I own binoculars that needed serious alignment and I achieved making these binoculars usable by turning the prism tilt screws to merge the images.
Tilting binocular prisms can have the dramatic affect of considerably reducing the amount of light through the binocular optics. The shape of the binocular exit pupil image can be observed to directly assess the amount of light being lost. Perfectly round exit pupil images should be observed for a binocular to pass 100% of the light. Binoculars that have tilted prisms will exhibit a pointed oval shape to the exit pupil image indicating a light loss thru the binocular.
Ignore, for sake of this discussion, the sometimes seen squared off edges in the exit pupil image caused by undersized prisms. Unless grossly undersized, this vignetting will not impart as significant a loss of light as might be induced by tilting the prisms.
Precise measurement of exit pupil images with a micrometer is required to calculate the amount of light loss induced by tilted prisms. The results of one example calculation are given here. A pair of 20x80 binoculars that should have a fully round exit pupil of 4mm was adjusted to acquire a merged image. The exit pupil measured still a full 4mm in one dimension, but only 3.2mm in the narrowed dimension. An accurate calculation of the area obscured by the tilted prism proves that nearly 26% of the area is lost.
Simplified A=pi r2, 80mm lenses, if passing 100% of the light would pass 80x80= 6400 sq. mm. of light. Reduced by 26%, the same lenses pass only 6400 x 74% = 4736 sq. mm of light. The square root of 4736 gives the resultant of the equivalent diameter objective lens as 68.8mm. Therefore, 80mm binoculars with tilted prisms resulting in an exit pupil image narrowed by 20% in one dimension are effectively reduced to the equivalent of 69mm binoculars.
If you have tilted the prisms in only one barrel of your binoculars and they exhibit these symptoms, try using the same eye to compare the images thru both barrels of your binoculars. The light loss should be readily apparent.
I have written more on this subject and I would encourage discussion. You may refer to this article for more information. edz
http://www.cloudynights.com/howtos2/binoc-collimatin.htm
edited 11-26-02
If images are not aligned, but you are starting with nice round exit pupils, you can tilt the prisms to merge the out-of-collimation images, but you might then be moving the prisms out of alignment.
True collimation is the aligning of all the optical elements along the binocular optical axis. No optical element should be tilted from the optical axis.
I must admit that I own binoculars that needed serious alignment and I achieved making these binoculars usable by turning the prism tilt screws to merge the images.
Tilting binocular prisms can have the dramatic affect of considerably reducing the amount of light through the binocular optics. The shape of the binocular exit pupil image can be observed to directly assess the amount of light being lost. Perfectly round exit pupil images should be observed for a binocular to pass 100% of the light. Binoculars that have tilted prisms will exhibit a pointed oval shape to the exit pupil image indicating a light loss thru the binocular.
Ignore, for sake of this discussion, the sometimes seen squared off edges in the exit pupil image caused by undersized prisms. Unless grossly undersized, this vignetting will not impart as significant a loss of light as might be induced by tilting the prisms.
Precise measurement of exit pupil images with a micrometer is required to calculate the amount of light loss induced by tilted prisms. The results of one example calculation are given here. A pair of 20x80 binoculars that should have a fully round exit pupil of 4mm was adjusted to acquire a merged image. The exit pupil measured still a full 4mm in one dimension, but only 3.2mm in the narrowed dimension. An accurate calculation of the area obscured by the tilted prism proves that nearly 26% of the area is lost.
Simplified A=pi r2, 80mm lenses, if passing 100% of the light would pass 80x80= 6400 sq. mm. of light. Reduced by 26%, the same lenses pass only 6400 x 74% = 4736 sq. mm of light. The square root of 4736 gives the resultant of the equivalent diameter objective lens as 68.8mm. Therefore, 80mm binoculars with tilted prisms resulting in an exit pupil image narrowed by 20% in one dimension are effectively reduced to the equivalent of 69mm binoculars.
If you have tilted the prisms in only one barrel of your binoculars and they exhibit these symptoms, try using the same eye to compare the images thru both barrels of your binoculars. The light loss should be readily apparent.
I have written more on this subject and I would encourage discussion. You may refer to this article for more information. edz
http://www.cloudynights.com/howtos2/binoc-collimatin.htm
