Should I open another thread for my other question?
How do the distortions discussed describe what happens to the view when the users actual IPD is less than the minimum closure of the hinge?
My IPD is 53mm (under the 5th percentile by one chart I saw).
Most bins only go down to 55mm or 56mm.
In fact, I purchased Zeiss Conquest HD 10x42 and 8x32 because they seem to be the only brand at that quality level (Beta?) whose stated IPD goes down to 54mm.
I can choose to either center one eye, which becomes dominant in my viewing, and maybe negates much of the advantages of using a BI-nocular; or try to equalize the off-centering (which seems to be harder to utilize without eyestrain & vignetting).
I can also back my eyes away further, which reduces my FOV but seems to help when at close focus (my birdfeeder is ~20-25 feet away from the window). Which is odd, since isn't the binocular doing the all xxx accomodation xxx EDIT - I meant to say CONVERGENCE - at any focal distance? Should not my pupils be at "infinity" gazing into the ocular, no matter what the binocular focal distance is ? Does having a too-small IPD cause at least one eye to converge & suffer eyestrain?
EDIT: my opthalmologist & his glasses fitter were unable to answer my question "for binoculars, are my pupils at a distance of Close IPD, Intermediate, or Far." * The fitter measured me at her arm's distance, for "office" strength Transitions lenses. I am slightly nearsighted. She said the rule of thumb is to add 1.5mm per eye to determine Far IPD.
* American and British usage of these terms differs.
EDIT - getting more terminology from a previous topic, esp. re some effects Porros have at close range.
see birdforum.net/threads/is-3-d-more-natural-in-porros-or-roofs.425235/page-2
Great pictures, especially the enhanced hearing one 👍
www.birdforum.net
Omid Post# 24
...The exact technical answer to your question is that both models provide diminished stereoscopic effect for far objects. In other words, binoculars deliver L and R images whose stereoscopic parallax does not match the dioptric distance of the images seen through the eyepieces. As a result, binoculars create vergence-accommodation conflict in the human eye.
L-R Parallax: amplified M-times and further multiplied by the ratio of objective IPD to eyepiece IPD if applicable
Accommodation demand: amplified MxM-times then a constant value (depending on focus knob position) is added to it or subtracted from it.
Resolving the conflict between accommodation (eye focus) and parallax (eye convergence) requires that the objectives are separated M-times larger than the observer's IPD. A stereoscopic viewing condition in which parallax and focus are consistent is called "Ortho-stereoscopy". It is discussed very rarely in texts. There is a brief review in Le Grand (Form and Space Vision, 1967) on page 312 just before he ends his book on page 313. The formula there is consistent with my own calculation that ortho-stereoscopy in binoculars requires M-times larger IPD on the objective end. For a 10X binocular, this require approximately 65cm separation between the objectives (obviously not practical).