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Which roofs are better for their 3D view?

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Old Wednesday 16th May 2018, 17:38   #51
dries1
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Thanks Bill, I have to support that statement. This morning I took the SE 8X32 and a Leica 8X42 HD and viewed some branches in my back yard the distance is ~ 60 feet away. While there is some obvious spatial 3-D with the Leica with branches 6 inches to a foot apart at that distance, other thin branches closer together 2-3 inches, blend in with view. With the SE I am able to easily distinguish the 3-D view with these small diameter branches 2 inches apart. I have always appreciated this feature of the porro design, and I can spot small critters in the bush easier than any roof. One of my friends who is a hunter uses Docter 8X56 and 10X56 porros, he says the same thing regarding porros, many of his friends switched to roofs simply for the lighter weight and smaller dimensions, not for the better view.

Andy W.
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Old Wednesday 16th May 2018, 18:07   #52
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Hello Andy,

Roof prism binoculars were never about a better view; they were popular for compactness and weight. With the possible exception of close focussing, there is no reason for a Porro to be optically inferior to a roof. Until the advent of phase coating, the roof prism binoculars were optically inferior, in contrast and in resolution.

Happy bird watching,
Arthur
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Old Wednesday 16th May 2018, 18:17   #53
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Originally Posted by dries1 View Post
Thanks Bill, I have to support that statement. This morning I took the SE 8X32 and a Leica 8X42 HD and viewed some branches in my back yard the distance is ~ 60 feet away. While there is some obvious spatial 3-D with the Leica with branches 6 inches to a foot apart at that distance, other thin branches closer together 2-3 inches, blend in with view. With the SE I am able to easily distinguish the 3-D view with these small diameter branches 2 inches apart. I have always appreciated this feature of the porro design, and I can spot small critters in the bush easier than any roof. One of my friends who is a hunter uses Docter 8X56 and 10X56 porros, he says the same thing regarding porros, many of his friends switched to roofs simply for the lighter weight and smaller dimensions, not for the better view.

Andy W.
Thank, Andy:

I’m totally onboard with your observations. However, just remember others may not be; the best shrink in the world is at a loss when trying to reason what is going on between someone’s ears. I once saw an “idiot savant” tested for his ability to be given ANY DATE of ANY YEAR of ANY CENTURY and without hesitation tell you what day of the week it was—based on our calendar—with 100% accuracy. We are only beginning to understand man’s potential.

To err is human; to really foul things up requires a computer.

Bill
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Old Wednesday 16th May 2018, 18:18   #54
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Hello Andy,

Roof prism binoculars were never about a better view; they were popular for compactness and weight. With the possible exception of close focussing, there is no reason for a Porro to be optically inferior to a roof. Until the advent of phase coating, the roof prism binoculars were optically inferior, in contrast and in resolution.

Happy bird watching,
Arthur
AMEN!

Bill
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Old Wednesday 16th May 2018, 19:26   #55
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Arthur,

Once again you always clear things up for me. Thanks.

Andy W.
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Old Wednesday 16th May 2018, 20:34   #56
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With a 6 yard baseline and 28x magnification, the baseline is about 90 times an average IPD.
Here the objective spacing has more contribution than the magnification.
Of course these naval rangefinders have very large components from both the objective spacing and magnification.

Another interesting variant is the long distance rangefinder that uses the curvature of the earth as the means of distance measure.
The operating height of the instrument is known. The target ship is identified and the size and height above sea level is known, so it is fairly simple to work out the distance by how high above the horizon the control station of the target ship seems to be.

Using, say 8x binoculars, a Porroprism binocular with the wider objective spacing compared to a roof prism binocular will give twice as much stereo effect.
Of course this is significant.
But both bring things 8x closer and this magnification has more effect than the two times due to the wider Porroprism objective spacing.
Hand held the magnification contribution might be reduced to about 5x because of hand tremor.
With the Porroprism binocular still having a 2x advantage over the roof prism binocular.

Last edited by Binastro : Wednesday 16th May 2018 at 20:48.
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Old Wednesday 16th May 2018, 20:51   #57
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With a 6 yard baseline and 28x magnification, the baseline is about 90 times an average IPD.
Here the objective spacing has more contribution than the magnification.
Of course these naval rangefinders have very large components from both the objective spacing and magnification.

Another interesting variant is the long distance rangefinder that uses the curvature of the earth as the means of distance measure.
The operating height of the instrument is known. The target ship is identified and the size and height above sea level is known, so it is fairly simple to work out the distance by how high above the horizon the control station of the target ship seems to be.

Using, say 8x binoculars, a Porroprism binocular with the wider objective spacing compared to a roof prism binocular will give twice as much stereo effect.
Of course this is significant.
But both bring things 8x closer and this magnification has more effect than the two times due to the wider Porroprism objective spacing.
Hand held the magnification contribution might be reduced to about 5x because of hand tremor.
With the Porroprism binocular still having a 2x advantage over the roof prism binocular.
Hi, Binastro:

“Height of the Eye” is, without a doubt, a very important concept for most of the world’s navies to understand. However, based on what you have just said, it would appear those navies have spent BILLIONS of dollars, pounds, marks, yen, etc. designing, building, repairing, and maintaining superfluous gear. Am I wrong?

A person with a hi res, 48-inch TV—sitting 6 feet from it—will have a much nicer view than his friend who pays $11.50 for a small bag of popcorn and a small soft drink and gets to sit near the back of a theater to watch the same movie. Yet, people are still doing it.

Wherein does the truth lie? Some say, “There’s no accounting for taste.” They all should.

Bill
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Old Wednesday 16th May 2018, 21:02   #58
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I would think that a coincident or stereo rangefinder is more accurate than the rangefinders using the earth's curvature.
The height above the horizon varies with the weather, anomalous refraction and mirages. But these horizon rangefinders were used.
Vertical heights are affected by mirages, but horizontal distances very little.

For gunnery the coincident or stereo rangefinder would be superior.
But I think Bismarck had radar controlled guns.

Nowadays laser rangefinders are far more accurate, as probably is modern radar.

As for T.V. at home compared to a cinema. The cinema is much more immersive and impressive.
I remember watching Top Gun, I think, in a cinema and the climbing F14 Tomcats were spectacular.
At home nothing seems to happen as the aircraft climb. Most disappointing on T.V.
I am not sure I ever went to an outdoor cinema as happens in the U.S.

I saw recently a Panasonic 77 inch T.V. advertised at about £10,000. I think a cinema visit is the better option.

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Old Wednesday 16th May 2018, 21:16   #59
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But I think Bismarck had radar controlled guns.
Yes, but YOURS were better!

I think, as an aside, it is nice to point out that Bismarck, Tirpitz, Yamato, and Musashi all learned—the hard way—that the days of conflicts between large, expensive battlewagons were over. Three of the four mentioned were sunk by airpower—after spending much of their lives in hiding—and although the Bismark was sunk after a barrage of projectiles and torpedoes it was slowed and made to go in circles because of a torpedo from a Swordfish ... biplane jammed the rudder!

Bill

PS Yes, Bismarck WAS scuttled. BUT, it wasn't going to make it to Brest, anyway. In his 1960 hit, Sink the Bismarck, Johnny Horton sang, "the FIRST shell hit the bismarck, they knew she couldn't last." Well, that's taking poetic license to the max! There were 2,700 projectiles, 8 inches or above, fired at the beast.
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Old Wednesday 16th May 2018, 21:23   #60
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At this point, we might enjoy a side trip down memory lane, circa 2006.
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Old Wednesday 16th May 2018, 21:46   #61
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What was a great surprise to me was to be informed recently by a world class satellite expert the following.

The so called parabolic flights to simulate weightless conditions, in I think strengthened Boeing 727s, cannot be parabolas. They must be ellipses.

Furthermore, and negating my teaching on projectiles is that shells, bullets etc, travel in ellipses not parabolas. These are of course modified by air resistance.

Satellites do not travel in parabolas if you want to stay in orbit, they travel in ellipses, as do all these other projectiles under the influence of gravity.
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Old Wednesday 16th May 2018, 22:25   #62
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The physics is well known. See HERE.

Just to keep it simple, and avoid BB stacking habits:
Quote:
@MaxW. When solving physics problems, one always has to make assumptions and simplify things, otherwise, the problem may end up having infinite degrees of freedom becoming impossible to solve. In this particular situation, it may or may not be the case. If you neglect earth’s curvature, the flat earth is the sin of the angle formed by the starting point, the ending point, and the center of earth. For small angles the sin of an angle becomes equivalent to the arc length. – J. Manuel Dec 8 '17 at 20:22
Got that?

Ed
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Old Wednesday 16th May 2018, 23:20   #63
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But when it comes to simulating zero-gravity, the flight path is approximated by a parabola.
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Old Thursday 17th May 2018, 01:17   #64
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Furthermore, and negating my teaching on projectiles is that shells, bullets etc, travel in ellipses not parabolas. These are of course modified by air resistance.
It is approximated by a parabola. The approximation is the curvature of the earth is assumed to be 0 and the slight variation of the gravitational field is assumed to be constant.

An Newtonian dynamics is itself an approximation, neglecting relativistic effects. What does this have to do with optics?
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Old Thursday 17th May 2018, 06:08   #65
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Hi,

Quote:
Originally Posted by Binastro View Post
Using, say 8x binoculars, a Porroprism binocular with the wider objective spacing compared to a roof prism binocular will give twice as much stereo effect.
Of course this is significant.
But both bring things 8x closer and this magnification has more effect than the two times due to the wider Porroprism objective spacing.
Why does magnificaton incrase the stereoscopic effect? Maybe I'm confused by my stereophotography experience .... there, if you increase focal length, you need to increase objective spacing to preserve the stereoscopic relationship.

However, admittedly if you don't follow that practice, you still get stereoscopic pictures, but the "scale" will be off, with objects appearing overly large.

Regards,

Henning
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Old Thursday 17th May 2018, 15:02   #66
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Thanks Ed,
I enjoyed reading that.

b3rd.
What does this have to do with optics.
Not much, except that long held ideas may be wrong, and light rays can be bent by gravity I suppose.
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Old Thursday 17th May 2018, 16:01   #67
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It is approximated by a parabola. The approximation is the curvature of the earth is assumed to be 0 and the slight variation of the gravitational field is assumed to be constant.

An Newtonian dynamics is itself an approximation, neglecting relativistic effects. What does this have to do with optics?
Although this thread started with the same old-same old we have heard at birdathons and amateur astronomy gatherings for years, it advanced into one of the most informative and—for me—useful offerings I have enjoyed in my 13 years here. There can be no doubt there has been some diverging from a concrete path ... and, in the name of light-hearted camaraderie, I have certainly been part of that. However, I have long known that every OPTICAL concept cannot be adequately explained by sticking strictly to OPTICS. Often the explanation that gets remembered is the one that walked through the back door. Sometimes we just don’t know what we don’t know.

Binastro said: “Not much, except that long held ideas may be wrong, and light rays can be bent by gravity I suppose.”

I say: On a minute scale, isn’t this the mover and shaker behind DIFFRACTION?

Just a thought,

Bill
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Old Thursday 17th May 2018, 16:42   #68
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An 8x roof prism binocular with IPD spacing of objectives amplifies the two separate images that differ by a small angle by 8x.

At a distance, there may be no stereo image at all with the unaided eyes, but the binocular clearly shows a stereo image.

And yes the 8x binocular makes things look 8x bigger or 8x nearer.

P.S.
Completely off topic (:

Yesterday, the milkman delivered 4 bottles of milk.
Why is this noteworthy?
The bottles are clear glass old style bottles, not plastic bottles.

I haven't seen these for many years.
Maybe the environment will be a bit better.
And maybe birds won't eat plastic or have plastic rings round their necks.

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Old Thursday 17th May 2018, 20:40   #69
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Hi,

Why does magnification increase the stereoscopic effect? Maybe I'm confused by my stereophotography experience .... there, if you increase focal length, you need to increase objective spacing to preserve the stereoscopic relationship.

However, admittedly if you don't follow that practice, you still get stereoscopic pictures, but the "scale" will be off, with objects appearing overly large.

Regards,

Henning
Hi Henning,

Sorry to disagree with David, but in response to your question the evidence doesn't support the notion that magnification increases the stereoscopic effect, i.e., 3-D perception, either using one eye or two. In fact, it supports the opposite, i.e., that magnification reduces the 3D effect.

The first attached article addresses lens loupes and surgical microscopes. The second addresses, radial distance perception as a function of magnification and optical truncation. On pg. 181 there is a relevant discussion about extending the results to field telescopes (and presumably binoculars).

There's also interesting material relevant to scaling effects.

Ed
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Old Thursday 17th May 2018, 21:23   #70
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It depends on the distance of the objects one is looking at.

If I am in the street with the pigeons around my feet and out to say 3 metres then viewing them is best with unaided eyes or with glasses. This gives the maximum depth of field, and stereo. Binoculars are not much use here.

But looking at objects around 100m away, there will be no stereo effect between close planes with unaided eyes.
It is probably best there to use a 10x binocular, which will separate 3 planes at 90m, 100m and 110m, all in focus or nearly so.

At medium distance, say 30m or 40m, the 10x binocular will not be suitable because the depth of field is small.
A 7x binocular will have a greater depth of field and separate 3 planes all in focus or almost in focus.
The 10x binocular will only manage 2 planes in focus.
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Old Thursday 17th May 2018, 23:48   #71
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It depends on the distance of the objects one is looking at.

If I am in the street with the pigeons around my feet and out to say 3 metres then viewing them is best with unaided eyes or with glasses. This gives the maximum depth of field, and stereo. Binoculars are not much use here.

But looking at objects around 100m away, there will be no stereo effect between close planes with unaided eyes.
It is probably best there to use a 10x binocular, which will separate 3 planes at 90m, 100m and 110m, all in focus or nearly so.

At medium distance, say 30m or 40m, the 10x binocular will not be suitable because the depth of field is small.
A 7x binocular will have a greater depth of field and separate 3 planes all in focus or almost in focus.
The 10x binocular will only manage 2 planes in focus.
David,

Two monocular factors account for what you're saying: 1) retinal image size and 2) depth of field. Distant objects, such as airplanes, increase in retinal image size with telescope magnification (M), but this is accompanied by a decrease in depth-of-field by a factor of 1/M^2. Hence, the object sizes of the various airplanes and defocus gradients provide perceptual cues as to relative distance. The value of binoculars vs telescope at that distance isn't much, as a biocular would do just as well.

Ed
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Old Friday 18th May 2018, 07:23   #72
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Hi Ed.
I haven't read your links but a surgeon using magnifying binocular glasses at close range is quite different to using a binocular at 30m, 40m or 100m.

With say a 10x binocular I can see the stereo separation of several close planes at 100m. This is not monocular clues but actual stereo separation.
With a magnification of 1x, i.e unaided eyes plus glasses I see no stereo effect although I might infer which plane is nearest or furthest.

Close up one can have too much magnification and too much stereo.

Incidentally, I asked my dental surgeon about using a mirror and direct view when he is operating on teeth.
He says he can flip back and forth without even thinking about it.

I asked how long it took to learn this skill.
He jokingly said that he killed the first 3 patients but afterwards he was fine.

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