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Tero wrote:

If I ever get a good chance to check out Nikon Premier SE 8x32, I might be interested in porros again.

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A couple of weeks ago I ran across a new pair of Nikon EII 8x30 porros on the bottom shelf of a camera store for $295. The views were certainly a WOW! I almost purchased them. However, in many ways, they duplicate my Swift Audubon Ed 8.5x44 porros. So I passed them up.

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Bob
38° Kentucky, USA

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But, some of us do not like the porro effect! I will take the brightness, but the wide spacing does some funny thing to my brain. After staring at close by objects less than 50 ft away for minutes, porros give me a focusing problem. My eyes don't seem to relax and I keep trying to focus and keep the object in view and clear. Perhaps I am overly sensitive to alignment problems, but I never have this problem with roofs or reverse porros.

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Tero wrote:

I really can't explain the problem I had, but I imagine it is lumped under eye strain.

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EdZ wrote:

The affect could become particularly annoying at closer distances, since the angles of convergence to the objects in the view would be larger.

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I know what Tero and EdZ mean about eye strain while using porros during close up observing.

. . .

A few minutes ago, I began to observe three large dragonflies doing some kind of air dance in my yard. I observed the dragonfly dance, first with the Swift Audubon 820Ed 8.5x44 porros, and then with the Leopold Katmai 6x32 roofs, alternating the views every two minutes for over 30 minutes of total observing.

The dragonfly dance was very erratic--the dragonflies stayed within a 200-foot area, however, their dance had no definite course within this area, flying as high as 20 feet on one pass and dropping instantly to two feet for a few yards, and then back up to 15 feet; all the while weaving in several yards closer to me and then out many more yards further away. When I observed the dance with the porros, I noticed the definite three-dimensional imaging discussed earlier in this thread. However, while observing the dance with the roofs--which had just as much depth of field--I noticed the 3D effect was not pronounced.

After a few rounds of exchanging the roofs and the porros, the porros began to give me eye strain and a queazy feeling in my stomach. Every time I switched to the roofs, I could feel the eye strain and queaziness subside.

The only cause for this discomfort, that I could determine, was the enhanced 3D effect of the porros. Moving the porros rapidly to follow the dragonfly dance across the 3D background began to fatigue me; while the roofs easily kept up with the dragonfly dance and produced more pleasurable observing.

. . .

Thoughts anyone?

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Bob
38° Kentucky, USA



Edited by BobinKy (08/25/07 06:14 PM)

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EdZ:

My brain is old and wrinkled. I do not understand what you are telling me. Can you be a bit more specific?

Thanks.

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EdZ wrote:

Have you determined how much discomfort might be due to field curvature ?

Have you determined how much might be due to pincushion or lack of, and the consequent rolling ball effect ?

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Ok--I am trying to understand the terms above in red. So I googled the term "binocular" with each of these terms. I was able to learn something about them in the following online reports.

Abrahams, Peter (2006). Binoculars for Astronomy. Published by The Rose City Astronomers. Retrieved Sunday, August 26, 2007, from http://www.rca-omsi.org/binos.htm

Harrington, Phil (n.d.) How To Test Binoculars. Published by the Upstate NY & PA Public Education Astronomy Resource Site. Retrieved Sunday, August 26, 2007, from http://www.upstateastro.org/stars/binotest.html

Merlitz, Holger (n.d.). Review: Kronos BPO 10x50 vs. Kronos BP 12x40 vs. Baigish BPOc 10x42. Homepage of Holger Merlitz. Retrieved August 26, 2007, from http://www.holgermerlitz.de/kronos10x50.html

Merlitz, Holger (n.d.). The globe effect (rolling-ball effect) and its relation to pincushion distortion. Homepage of Holger Merlitz. Retrieved August 26, 2007, from http://www.holgermerlitz.de/globe.pdf

So, I grabbed the two binoculars in question--Swift Audubon 820ED 8.5x44 porro and Leupold Katmai 6x32 roof--and headed for my patio on this sunny afternoon. There were no dragonflies around, at least none of the large dancing dragonflies that I saw the day before. But I was fortunate to locate four Cabbage White butterflies fluttering about the mint in my garden.

I repeated the observation from yesterday, as much as possible. However, this time I was on the lookout for optical distortions, such as field curvature, pincushion, and rolling-ball effects.

And like yesterday with the dragonfly dance, I noticed the discomfort increased when I observed the fluttering butterflies up close with the Swift Audubon porros and subsided when I observed the same fluttering butterflies at the same distance with the Leupold Katmai roofs.

Employing the fence post test recommended by Phil Harrington, I noticed both binoculars demonstrated some field curvature, of the positive, or pincushion type (vertical lines of the fence post bending outward at the top and bottom, convex). However, from what I read in all of the above reports, a small amount of field curvature is good, since it compensates for the rolling-ball effect--the image seeming to roll over the surface of a ball, appearing a little larger in the center and seeming to shrink when shifted close to the edge. In fact Holger Merlitz indicated in his review of the military binoculars that pincushion distortion is beneficial for surveillance applications, where an area needs to be kept under observation.

So I rule out field curvature, pincushion distortion, and the rolling-ball effect as the cause of the discomfort.

Besides the 3D or stereoscopic vision differences, I noticed two other differences between the binoculars when following the flutter of the Cabbage White butterflies:

(1) depth of field was less with the porros, meaning the trees in the background were more out of focus, than with the roofs; and

(2) the 8.5x magnification of the porros made the out-of-focus trees appear larger, than with the 6x magnification of the roofs.

So, is the discomfort I feel while following the erratic flight of dragonflies and butterflies due to the porro's

(a) enhanced stereoscopic vision (3D or porro effect),

(b) more shallow depth of field,

(c) greater magnification, or

(d) something else entirely?

Whatever--the discomfort comes when I use the Swift Audubon porros to follow up at a close distance the erratic flight of insects (and presumably birds), and the discomfort subsides when I switch instruments and observe with the Leupold Katmai roofs.

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Bob
38° Kentucky, USA



Edited by BobinKy (08/26/07 05:59 PM)

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I held the binocular up to the light and backed away from the eyepieces and the exit pupils (5.3mm) were perfectly round. Since this is a "compact", in 6x32mm, you don't get the square exit pupils typical of BK-7 prisms associated with full size binoculars.

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