Chosun Juan
Given to Fly
I hope Omid will be paying tuition fee$ to the member$ here ! :brains:Omid and Tenex set up the question, and Henry hits it out of the park.
Well done, and thank you.
-Bill
Chosun :gh:
I hope Omid will be paying tuition fee$ to the member$ here ! :brains:Omid and Tenex set up the question, and Henry hits it out of the park.
Well done, and thank you.
-Bill
....but life is cruel so gradually you will lose accommodation as you eye's lens stiffens and by the time you're 30 or 40 you will definitely want a focusing mechanism on your binoculars.
The reason DOF appears shallow in binoculars and scopes is because ...
Old 20x50 Porros can be a problem, but not much for me. I find them very useful as night as much fainter stars are visible than in a 10x50.
B.
Hi Henry,
Thank you for your explanation. It is an interesting perspective and might be the correct reason why binoculars provide a shallow depth of field. However, we have not fully solved the mystery yet. What I like to understand is that why a healthy human eye can not focus on individual objects located at various distances while looking through binoculars? I am not saying why those objects don't all appear sharp. I am asking why it is not possible to look at individual image points and see them in sharp focus?
To use a camera analogy, the COTAX AX camera with a 50mm f/1.4 lens mentioned above can focus on any point in a scene (say from 1m to infinity). If the aperture is at f/1.4, other points slightly before or after the object on which the camera has focused will appear blurry. But it is possible to focus on any desired distance.
Why can't human eye -when positioned behind an eyepiece- do the same? Why can't we focus on various objects in front of our binoculars and see a shallow-depth-of-field view of only the object we are concentrating on?
-Omid
Yes, Henry's post answered this question. The eye has only a limited range of accommodation, which is more than adequate for the entire range of distance with unaided vision (which after all it evolved for!) but cannot handle the proportionally greater amount of defocus that comes from typical magnifications of 8x or more. And this only gets worse with age.What I like to understand is that why a healthy human eye can not focus on individual objects located at various distances while looking through binoculars? I am not saying why those objects don't all appear sharp. I am asking why it is not possible to look at individual image points and see them in sharp focus?
Yes, Henry's post answered this question. The eye has only a limited range of accommodation, which is more than adequate for the entire range of distance with unaided vision (which after all it evolved for!) but cannot handle the proportionally greater amount of defocus that comes from typical magnifications of 8x or more. And this only gets worse with age.
...Autofocus in cameras is now so precise, I think that autofocus binoculars should be looked at again...
Omid, This depiction of L.A. is far more realistic...
https://www.youtube.com/watch?v=N-BmxK-0Jts&list=PLFv4y-PVQCXAzzp181XIut2hCBb5wGwIC
-Bill
Omid, This depiction of L.A. is far more realistic...
https://www.youtube.com/watch?v=N-BmxK-0Jts&list=PLFv4y-PVQCXAzzp181XIut2hCBb5wGwIC
-Bill
Ha ha ha!! At 2:50 in the video it says go to Marina del Ray and park at the Coffee Bean!! That's walking distance from where I live
Should? According to what? We don't get to make up the laws of optics, or facts of biology. But if you still want to try, you could invite Rico to enjoy the afternoon at your café, and see who can project an image farthest...If a healthy eye can focus from 20cm to infinity; the same eye with a 10X binocular in front of it should be able to focus from 2m to infinity.
Should? According to what? We don't get to make up the laws of optics, or facts of biology.
Sure enough... so now instead of imagining how the eye "should" be able to focus anyway, you have to first envision what it means for an object to be out of focus (because something at another distance is in focus). The rays from this object are converging in front of or behind the retina instead of nicely on it, and the question is by how much, and whether the lens can distort enough to bring that focus onto the retina instead. Normally it can. (A diagram might help, like those at this DOF tutorial at Cambridge in Color.)According to the definition of an afocal system. An afocal system manipulates angles of rays by a simple multiplication factor M as I have shown in the attached drawing.
Sure enough... so now instead of imagining how the eye "should" be able to focus anyway, you have to first envision what it means for an object to be out of focus (because something at another distance is in focus). The rays from this object are converging in front of or behind the retina instead of nicely on it, and the question is by how much, and whether the lens can distort enough to bring that focus onto the retina instead. Normally it can. (A diagram might help, like those at this DOF tutorial at Cambridge in Color.)
Now put a 10x binocular in front of the eye: all the angles get multiplied accordingly, so the difference between the angles subtended by the two objects also does. The distance by which that convergence misses the retina increases dramatically, along with the diameter of the "circle of confusion" for that object. Now it's way out of focus, not just more than before but more of a blur than anything encountered in unaided vision. Can the eye lens distort enough now to correct even for that? No, it can no longer shift focus to this object without adjusting other lens(es) in the system.