Wogpotter, your definition of parallax is the distance between two images on a single plane in an optical axis. I've never heard of that.
My definition is the popular one; the displacement or difference in the apparent position of an object relative to another viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. This is the one I used teaching meter reading when the needle's an eighth of an inch or so above the scales. Or when teaching optical sterescopic rangefinder operation for long range gunfire.
These are two different things. With mine, if the angle's zero, there is no parallax. With yours, there's always parallax because the images are separated by some distance on the optical axis even though the angular difference is zero.
So, unless we use the same system of measurement and/or definition, we'll have two different perspectives.
My definition is the popular one; the displacement or difference in the apparent position of an object relative to another viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. This is the one I used teaching meter reading when the needle's an eighth of an inch or so above the scales. Or when teaching optical sterescopic rangefinder operation for long range gunfire.
These are two different things. With mine, if the angle's zero, there is no parallax. With yours, there's always parallax because the images are separated by some distance on the optical axis even though the angular difference is zero.
So, unless we use the same system of measurement and/or definition, we'll have two different perspectives.