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Ultravid comparison? (1 Viewer)
- Thread starter phyllosc
- Start date
Leif said:
Leif,
I wonder if it has to do with individual IPD. My normal IPD is 57mm so I can easily adjust downward on the SE. Perhaps those with higher IPD's have less latitude and are, therefore, happier with roofs.
This is just one more bit of anecdotal evidence to support the notion that individual preferences reign supreme.
John
elkcub
Silicon Valley, California
kabsetz said:
Kimmo,
My compliments on an excellent explanation. I also like your novel idea about consumer preferences based on in-store evaluations, and the future challenge of optics that converge.
My take on everyone's comments is that the eyes converge so as to maintain corresponding foreground object images on each retina. The wider apart the binoc's optical axes are to start with, the farther out convergence must be initiated. Without physically moving the oculars closer, the convergence limit should be roughly half the exit pupil diameter (i.e., as a tangent function of the eye's rotation angle). At closer focusing distances, if the oculars are then brought together somewhere around half the exit pupil diameter, the eye could essentially look cross-axis to the maximum extent (based on my limited optical knowledge). In practice the max cross-angle is probably not realized for several reasons, but 3±e mm does seem reasonable considering typical exit pupil sizes.
Other factors aside, if this were true it would follow that: (1) larger exit pupils should aid close focusing, (2) reverse porros should be easier to close-focus than standard porros (or roofs). Folks with narrow IPDs should be able to focus closer than those with wide IPDs. When the close focus of the optics is nearer than these convergence limits allow — only one eye could be used effectively.
-elk
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Elk, you are quite right. Viewing close is easiest with reverse porros, although for purely geometrical reasons the advantage of reverse porros over roofs is not as large as that of roofs over traditional porros. Large exit pupils would help in the sense that they would slightly lessen the need/benefit of adjusting your IPD for close ranges. On the other hand, large exit pupil in a roof prism design puts limitations on the minimum IPD attainable, and in a traditional porro would not offset the handicap brought by the wider spacing of the optical axes. A reverse porro could be made with large exit pupils, but I do not know of one. The closest thing that comes to mind is the B&L Elite 8x50 with its underslung prism assemblies, a binocular that I have never seen or held.
Kimmo
Kimmo
