Which roofs are better for their 3D view? (1 Viewer)

Binastro · May 16, 2018

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.

elkcub · May 16, 2018

The physics is well known. See HERE.

Just to keep it simple, and avoid BB stacking habits:

@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? :brains:

Ed

elkcub · May 17, 2018

But when it comes to simulating zero-gravity, the flight path is approximated by a parabola.

b3rd · May 17, 2018

Binastro said:
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?

Hauksen · May 17, 2018

Hi,

Binastro said:
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

Binastro · May 17, 2018

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.

WJC · May 17, 2018

b3rd said:
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? :cat:

Just a thought,

Bill

Binastro · May 17, 2018

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.

elkcub · May 17, 2018

Hauksen said:
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

Binastro · May 17, 2018

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.

elkcub · May 18, 2018

Binastro said:
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

Binastro · May 18, 2018

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.

Which roofs are better for their 3D view? (1 Viewer)

More options

Binastro

Well-known member

elkcub

Silicon Valley, California

elkcub

Silicon Valley, California

Attachments

b3rd

Reg1stered User

Hauksen

Forum member

Binastro

Well-known member

WJC

Well-known member

Binastro

Well-known member

elkcub

Silicon Valley, California

Attachments

Binastro

Well-known member

elkcub

Silicon Valley, California

Binastro

Well-known member

Similar threads

Users who are viewing this thread