Omid, post#210:
Position of the Virtual Image in Binoculars We all know that binoculars are Keplerian telescopes with an inverter (erector) prism added. Consider an ideal afocal telescope as shown in the attached diagram and ignore the erector prisms. Assume that the telescope's magnification power is 10X...
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Hi, I hope you agree with the technical literature that the astronomically used Kepler telescope is focused to infinity and the virtual image appears at infinity because the excellent rays of the ray optics are parallel - with a position of the real intermediate image in the focal plane of the eyepiece. With the focusing, for terrestrial, non-infinite observation distances, the eyepiece can be shifted so that the real intermediate image of the objective is also in the focal plane of the eyepiece. Consequently, I see no reason why the distances of virtual images and the corresponding accommodation of the eye lenses should change. The ideal viewing distance of a magnifying glass is, according to several literature references by teaching scientists, the focal plane. Because of me, individual observers may handle this differently, but without precise measurements (e.g. X-ray photography of binoculars adjusted by this observers knowing the focal lengths of objective and eyepiece), this will be a dispute about Emperor's beard.
With these considerations, I see no reason why my ray-optic constructions should be wrong. I would express the function of focusing better in the meantime: One shifts with it the focal plane of the eyepiece into the actual image distance of the objective (location of the real intermediate image > focal plane of the objective at non-infinite observation distance). With internal focusing, this is done by shifting additional internal lenses for objective or eyepiece. It depends only on a relative movement of eyepiece or objective focal plane.
From my ray-optical images, with some trigonometry, one can derive more accurate formulas for finite, terrestrially focused binoculars than are known from the astronomical Kepler telescope. I think this is where your calculation error lies for the distance of virtual images for finite observation distances.
post #211:
Position of the Virtual Image in Binoculars We all know that binoculars are Keplerian telescopes with an inverter (erector) prism added. Consider an ideal afocal telescope as shown in the attached diagram and ignore the erector prisms. Assume that the telescope's magnification power is 10X...
www.birdforum.net
The "Omid method " with my old analogue SLR camera (without film, without battery, only manual operation for cam and lens) does not and cannot work: Without calculating or using tables, 5 mm exit pupil corresponds to about f/11 for my cam lens (f=50mm; 1:1.8) with a depth of field of more than 3 m to infinity. So it seems more sensible to me to carry out the experiment at close range: No reliable results, the manual optical 3-field focus help of my non-autofocus lens hardly works with small EP of bins. In addition, you refocus close up and the virtual image shifts back towards infinity. So the observation distance doesn't matter. I have tried 3 m and 80 m distances. Besides, the whole shaky system (bins + SLR cam) is complex, I don't want to evaluate results.
From your description of Owen's method, I see that it is about the resting focus of the eye. Without binoculars, which could force one to deviate from the resting focus, e.g. infinite focusing of the eye, which according to my literature is also relaxed. Using this method as proof or evidence of intentional user modification of the virtual image of non-infinity binoculars is imho invalid.
So I prefer to leave it at what scientists write about the image perception and formation of magnifying glasses (= eye piece) and the astronomical Kepler telescope and apply that to finite-focus binoculars, unless I have a good reason to do otherwise. Do you know of a demonstrable reason?
Sorry, when I read your earlier posts, imho you are wrong several times or speculating regarding virtual image, its distance, necessary eye accomodation, ray optics from eye piece (Fig. 5 post #275 with wrong location of real intermediate image regarding focus plane of finite focused telescop eye pieces).
Best wishes. Jessie
