. Regarding the fields of view mentioned above.
Although these can be measured accurately using the stars it is important to compare the magnifications. Some binoculars that are marked as seven times are actually 6.7 times or 6.5 times.
All that is necessary is to compare the various binoculars with each other at a distance using saying a brick wall. It is not really necessary to exactly check the magnification.
If a genuine 7×35 binocular has a field of 11.0° and another has a 12.0° field but is only actually 6.5 times then they both have more or less the same apparent field of view.
The problem is further complicated by the fact that magnifications change across the field in various amounts with differing eyepieces.
In addition if the two fields of view don't exactly overlap then the field size appears to be more than it actually is in each half of the binocular. It is actually larger.
I sometimes deliberately slightly change the IPD from the correct value to get a slightly wider field of view.
A further measure of the actual inaccuracy of field sizes is that a handheld binocular even at seven times magnification has a wider field of view than if it is tripod mounted.
This is because hand tremor increases the real field of view somewhat and the persistence of vision sees a larger field of view handheld.
So when quoting fields of view the above points need to be borne in mind. And there may be other points that other observers may think of.
Although these can be measured accurately using the stars it is important to compare the magnifications. Some binoculars that are marked as seven times are actually 6.7 times or 6.5 times.
All that is necessary is to compare the various binoculars with each other at a distance using saying a brick wall. It is not really necessary to exactly check the magnification.
If a genuine 7×35 binocular has a field of 11.0° and another has a 12.0° field but is only actually 6.5 times then they both have more or less the same apparent field of view.
The problem is further complicated by the fact that magnifications change across the field in various amounts with differing eyepieces.
In addition if the two fields of view don't exactly overlap then the field size appears to be more than it actually is in each half of the binocular. It is actually larger.
I sometimes deliberately slightly change the IPD from the correct value to get a slightly wider field of view.
A further measure of the actual inaccuracy of field sizes is that a handheld binocular even at seven times magnification has a wider field of view than if it is tripod mounted.
This is because hand tremor increases the real field of view somewhat and the persistence of vision sees a larger field of view handheld.
So when quoting fields of view the above points need to be borne in mind. And there may be other points that other observers may think of.