Re: Seeing the curvature of the Earth directly
« Reply #40 on: February 11, 2019, 07:15:00 PM »
String with balloons attached may also make a string curve upward though. A solid metal that doesn't bend easy would be fine imo.

But a glober might not believe that the metal bars are straight. A tight string has to be very close to straight, and if it curves, its a simple matter to know which way it's curving.

Without the balloons, a some of your fellow flat earthers might say that it was just sagging and the apparent upward bulge of the horizon was just by comparison to the sagging string, which is why the balloons are important - *if* there was any measurable sag, it would be up, not down, so it makes the experiment rather bulletproof.

However we could always try the straight metal edges, and if that showed a curve then some are going doubt it, and then we can try with a tight string, and if that still shows a curve then we can try the tight string with the balloons and well then the horizon can't be curved.

One advantage of the string is that if it will be a lot easier to set up a perfectly straight 10 ft string up in the mountains as compared to trying to hike up a 10 ft metal  bar and keeping it straight.  And the reason it's important for it to be long is so you can have it go all the way across your field of view while still being some distance from the camera so that it can be in focus as well as the horizon being in focus. If the bar is too close to the camera, either it or the horizon will be blurry and it'll blur the issue.

Another advantage of the string is that it won't block the view above or blow itself like the metal bar will.

As you can tell, I'm very excited to get up in the mountains with some string and balloons, but at the moment we got record snows here and I need chains just to get to the grocery store so there's no mountain trips for me for a while.

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Offline Tom Bishop

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Re: Seeing the curvature of the Earth directly
« Reply #41 on: February 11, 2019, 09:15:02 PM »
So about barrel distortion, it curves straight lines around the center of the picture.

In reality, you would probably see a combination of curve plus barrel disortion, so the photo with the horizon above center would show more curve and the other would show less curve or straight, or a negative curve, but not as much of a curve as the above-center horizon photo.

One thing you can do is take a photo of a grid and analyse that. On my iPhone SE the lines about 109 pixels above and below the centre of the frame were straight, and the ones after that began to curve. That gives me a 218 pixel 'sweet spot', and the horizon occupies only about 10% of that.

Here's a compressed image of the grid:



And here's a picture of the horizon I took, with the mathematical prediction overlayed:



Next time I'm going to photograph the horizon with some straight metal bars placed just above and just below it, which I figure is the best demonstration that barrel distortion isn't causing the curve.

Cheers. :)

All cameras are affected by some amount of barrel distortion. An absurd test.



Compressed with your methods, compressing the width to 500 and stretching the height to 3000:



I guess the earth must be concave?  ::)
« Last Edit: February 11, 2019, 09:29:13 PM by Tom Bishop »

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Re: Seeing the curvature of the Earth directly
« Reply #42 on: February 11, 2019, 11:51:46 PM »
All cameras are affected by some amount of barrel distortion. An absurd test.

Yes, all lenses suffer some level of barrel distortion. However, when you go above 50mm the distortion levels get smaller and smaller to almost nil.

As well, you can pop into something like photoshop and specifically correct barrel distortion. Some cameras these days even let you correct for a specific lens in-camera.

And there are all kinds of tutorials and software around to 'de-fisheye' GoPro footage in Post.

Re: Seeing the curvature of the Earth directly
« Reply #43 on: February 12, 2019, 05:33:00 AM »
What camera was that photo taken with, Tom? Was the horizon centred in the frame? How does its distortion look when tested with a grid?

My suspicion is that you didn't take this photo, and that you purposefully chose one with a horizon located well below the centre of the frame, which we all know will significantly distort.

That aside, how about you go and do the test yourself? Do you have a camera? Can you find a place to photograph the horizon from above 400 feet?

If so, take the photo with the horizon perfectly centred, then do the vertical stretch and see what it shows. Then take a photo of a grid, such as this one, and do the same thing, to see how your camera is distorting.

Then compare the two images and also compare your stretched photo with the mathematical prediction for both flat earth and globe earth models.

Pure zeteticism. What possible reason could there be not to do it?
« Last Edit: February 12, 2019, 04:16:04 PM by Max_Almond »
If you've proven yourself immune to logic and incapable of reasonable debate, please understand that I won't be paying you much heed (this means you, George Jetson, Baby Thork, Sandokhan, Tom Bishop, and Totallackey).

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #44 on: February 12, 2019, 02:22:51 PM »
I guess the earth must be concave?  ::)
Tom, the image you selected is clearly not suitable for the suggested experiment as the horizon is well below the center of the image.  This should be obvious, especially if barrel distortion is suspected as was evidenced from your first comment.  Or do you really not know how optics work?  It is also obvious you did some other manipulation to the image too, making your result suspect.

For this experiment to work effectively, the horizon line must pass through the center of the lens to eliminate the effects of barrel or pincushion distortion.
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Offline Bad Puppy

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Re: Seeing the curvature of the Earth directly
« Reply #45 on: February 12, 2019, 09:33:30 PM »
Here you go Tom.  Do a bit of light reading.

https://lenspire.zeiss.com/photo/en/article/curved-images-of-straight-lines-what-is-distortion

Congratulations.  You've just proved yourself to be completely unqualified to offer any credible analysis on photography.
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Offline Tom Bishop

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Re: Seeing the curvature of the Earth directly
« Reply #46 on: February 13, 2019, 03:32:11 AM »
I posted it as an example of distortion. Learn to read.

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #47 on: February 13, 2019, 04:24:08 AM »
I posted it as an example of distortion. Learn to read.
Wonderful!  Not really stated as claimed, but quite demonstrative nonetheless ... and unfortunately a bit off topic as a result.

Now it would be great if you did the experiment correctly.

I'm currently vacationing in southern Florida, so I'll endeavor to attempt it over the next few days.

For lenses I have at my disposal both a Pentax FA* 24mm F2 and a Pentax FA 50mm F1.4 which are considered to be above average for these focal lengths in barrel distortion (See links below).  However, I will be using an APS sized sensor camera body (Pentax K3 II) ensuring only the sweet-spot of each lens will be used to form the image.  Of course the horizon will be placed directly at the vertical center of the image where any such distortion should be eliminated.  I will use Photoshop to do the transformations.  I will make the raw jpeg images available to anyone who wishes them.

Tom?


https://www.opticallimits.com/pentax/121-pentax-smc-fa-24mm-f2-al-if-review--lab-test-report?start=1


https://www.opticallimits.com/pentax/126-pentax-smc-fa-50mm-f14-review--lab-test-report?start=1
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Quote from: Tom Bishop - Zetetic Council Member
The moon's orbital path has a diameter of 768,000 km. That is almost one million miles.

Re: Seeing the curvature of the Earth directly
« Reply #48 on: February 13, 2019, 06:05:30 AM »
That sounds very good. You could also take a photo of this grid, and make that available for us to analyse:

If you've proven yourself immune to logic and incapable of reasonable debate, please understand that I won't be paying you much heed (this means you, George Jetson, Baby Thork, Sandokhan, Tom Bishop, and Totallackey).

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #49 on: February 13, 2019, 12:54:37 PM »
Max, there are grid shots from the tests of these lenses at those links I provided.  Do you still want me to provide more?
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Quote from: Tom Bishop - Zetetic Council Member
The moon's orbital path has a diameter of 768,000 km. That is almost one million miles.

Re: Seeing the curvature of the Earth directly
« Reply #50 on: February 13, 2019, 02:25:03 PM »
Thanks. I've clicked on the links now. :)

The grid above might be better though, or one similar. The more lines, the easier it is to see where distortion is present, and where the lens is shooting true. Plus, it'll show us your actual personal lens, which is a bonus.

In the meantime, I've knocked up a little frame with some bits I found lying round:



The ties are to squeeze it together a little to get the two edges as straight and parallel as possible. I've a little more work to do on it but the results are pretty nice:



As we can see, the two edges close to the centre remain pretty much straight, while the ones above and below reveal significant pincushion distortion.

Locate the horizon in the very centre of the image, between the two straight edges, and we can show that it retains its shape, which is a curve.

I'll be trying it out soon, from the 1500 foot hill nearby.
« Last Edit: February 13, 2019, 05:31:49 PM by Max_Almond »
If you've proven yourself immune to logic and incapable of reasonable debate, please understand that I won't be paying you much heed (this means you, George Jetson, Baby Thork, Sandokhan, Tom Bishop, and Totallackey).

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #51 on: February 13, 2019, 07:54:07 PM »
Here are the grid images for the 24mm lens.  I'm vacationing so could only take a picture of my laptop screen, hence it was difficult to keep things perfectly aligned.  However, it is clear that the center is not affected by any barrel/pincushion distortion, although I got a little slant on it.

« Last Edit: February 13, 2019, 07:57:59 PM by BillO »
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Quote from: Tom Bishop - Zetetic Council Member
The moon's orbital path has a diameter of 768,000 km. That is almost one million miles.

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #52 on: February 13, 2019, 07:56:33 PM »
Here is the same for the 50mm lens.  A bit better.

If anyone wants the raw files, just PM me an email address I can send them to.
Here a quack, there a quack, everywhere a quack quack.

Quote from: Tom Bishop - Zetetic Council Member
The moon's orbital path has a diameter of 768,000 km. That is almost one million miles.

Re: Seeing the curvature of the Earth directly
« Reply #53 on: February 14, 2019, 05:25:28 AM »
<snip>
All cameras are affected by some amount of barrel distortion. An absurd test.

Hmm, what if we used a pinhole on the camera instead of a lens? Would that eliminate the barrel distortion?
(I'm talking about like a DSLR here with a removable lens.)

Re: Seeing the curvature of the Earth directly
« Reply #54 on: February 14, 2019, 05:37:53 AM »
However, it is clear that the center is not affected by any barrel/pincushion distortion, although I got a little slant on it.

Nice one Bill, thanks for posting those.

The slant is actually the hardest bit of it, for me. What looks level to the eye can be massively slanted when stretched/compressed.

When I take the picture with the (levelled) metal frame I'll measure from camera to each edge, and hope that sorts it out.

Hmm, what if we used a pinhole on the camera instead of a lens? Would that eliminate the barrel distortion?

Yes. But, at the same time, as long as Bill gets it near the middle of the frame it's clear his lens isn't going to make straight lines curved.

I wonder where he'll be in Florida that'll give him 400 feet or more elevation?
« Last Edit: February 14, 2019, 10:13:45 AM by Max_Almond »
If you've proven yourself immune to logic and incapable of reasonable debate, please understand that I won't be paying you much heed (this means you, George Jetson, Baby Thork, Sandokhan, Tom Bishop, and Totallackey).

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Offline BillO

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Re: Seeing the curvature of the Earth directly
« Reply #55 on: February 14, 2019, 06:51:47 PM »
I wonder where he'll be in Florida that'll give him 400 feet or more elevation?
Why do you need the elevation?

Edit:  Never mind - just had to kick my brain into gear.  Well, that presents a problem.  I guess I could go looking for a tall building I could get up on, but other than that, I am SOL.  I'm still hear for another 2 weeks so maybe I'll find a solution.
« Last Edit: February 14, 2019, 07:19:03 PM by BillO »
Here a quack, there a quack, everywhere a quack quack.

Quote from: Tom Bishop - Zetetic Council Member
The moon's orbital path has a diameter of 768,000 km. That is almost one million miles.

Re: Seeing the curvature of the Earth directly
« Reply #56 on: February 14, 2019, 08:44:21 PM »
You can use Walter Bislin's very excellent globe earth/flat earth simulator to see what the horizon would look like from a given altitude and field of view.

The attachments show what the horizon would look like for the two lenses from 328 feet. It's not a massive curve from that altitude, hence why even more is better.
« Last Edit: February 14, 2019, 09:43:57 PM by Max_Almond »
If you've proven yourself immune to logic and incapable of reasonable debate, please understand that I won't be paying you much heed (this means you, George Jetson, Baby Thork, Sandokhan, Tom Bishop, and Totallackey).