Hi Brock,
Great to hear from you. This is just my observation as I've reviewed products (particularly Nikons) since I have been on board in the professional optics community. I can honestly say I have no idea as to how these products are engineered, but our roof prisms have more depth of focus then when I started. Nikon certainly answered the call with the EDG binoculars by including great depth of focus on all the roof prisms in the line. Again, not sure how its done, but just my observations.
All the best,
Mike
Thanks, Mike. As to how it's done, I gather from Henry's posts it's done with "smoke and mirrors."
We always read from Henry and others that DOF is a fixed number for any given binocular at a certain magnification. So in theory, at least, a Nikon 8x32 SE should have the same DOF as a Nikon 8x32 Premier (LXL). I actually measured the DOF between the two, and they were close but not exactly the same. However, in my observations in the field, they appear very different, with the SE showing "superior" depth perception compared to the LXL, which gives more of a 2-D representation.
Porros, by virtue of their dog-legged prism design with wider separated barrels usually give users a better sense of depth perception than the same configuration roof. But even among roofs of the same configuration, I've perceived differences in depth.
At least part of it has to do with focuser speed. The LXL's focuser turns from close focus to infinity in less than half a turn. This creates the impression of less depth since you're focusing through the range of focus at a faster speed than with slower focusing 8x32 roofs.
So sometimes you can peg an actual, quantifiable feature to the perception of depth, or as Frank likes to call it, "apparent depth of field." Other times, it's harder to peg down.
Prof. Edz over on Cloudy Nights contends that bins with field curvature create a better perception of depth, particularly if the edges aren't completely out of focus, because the inner image will be in focus and the outer image will be slightly out of focus and with a nudge you can bring it in focus. So you're eyes are focused on two different focal planes at the same time, giving the impression of greater depth.
Other people contend just the opposite, that binoculars with field flatteners give them a greater perception of depth because they can see both the centerfield and edges in focus at the same time. More field in focus = greater depth perception. That might be what you're experiencing with the EDG.
Exit pupil size vs. your entrance pupil size, lighting conditions, eye relief, the environment your observing - dense woods vs. open field, focus speed, and probably other factors play a part in differences in depth perception among binoculars.
Then there's the actual difference in depth of field created by different magnifications. A 12x bin will give you a "slice of life" at close range whereas a 7x bin will show noticeably more depth.
Whereas actual DOF is formulaic, the perception of depth is more fluid and user dependent. So I wouldn't dismiss your observations even if they didn't match mine, because perceptions vary from person to person.
However, if you have a large enough sample group, you might get a consensus. If you read a lot of reviews of a particular binocular, more often than not you'll find a consensus about the depth perception, with reviewers saying that one roof gives a greater perception of depth than another, which is probably associated with one or more of the factors listed above.
From my own observations, roof prism binoculars seem to be losing depth perception rather than gaining it, because increasingly more roofs are being made with fast focusers, which create the impression of shallower depth.
Brock
