Request for those going to Dallas this year

[John Dolva]

I think the location of subject and camera can be dervied by taking a birds eye view and using the photos to line up objects and projecting them back to the photographers location

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this is a simulation of a (slightly rotated) 3D uniform grid with one square appearing closer because the grayscale value is different viewed from diffent distances:

[John Dolva]

http://science.howst...question491.htm

Why does the moon look so much bigger when it is near the horizon?

Please copy/paste the following text to properly cite this HowStuffWorks article:

"Why does the moon look so much bigger when it is near the horizon?" 17 October 2000. HowStuffWorks.com. <http://science.howstuffworks.com/question491.htm> 09 November 2010.

This question has been pondered for hundreds if not thousands of years. This problem is commonly referred to as the moon illusion. Some have speculated that there is some effect that causes the atmosphere to act like a magnifying glass making the moon look bigger. It turns out that any distortion caused by the atmosphere would actually make the moon look a little smaller.

Most scientists agree that the reason the moon looks bigger is purely in our minds. Our mind interprets the things we see in interesting ways. For instance, if you look at any door frame you can see that it is rectangular. But if you were to sketch the outline of the door frame from the angle that you are looking at it, most likely you would sketch a trapezoid. Your mind adjusts the door so that you perceive it as a rectangle from whatever angle you look at it. That theory is called shape constancy.

http://static.howstuffworks.com/flash/question491-moon.swf

Drag the bottom picture of the man around and see how big he looks.

Take a look at the picture above. Both images of the person are the same size, but you perceive the one in back to be bigger. This is because your mind sees the hallway and decides that the back person is farther away that the front person, so your mind adjusts the size of the person to make up for the increased distance. This phenomenon is called size constancy.

Size constancy is happening all the time. If you look down the street and see a sports car about 50 feet away, and behind it, about 100 feet away is a big SUV, you know that the SUV is bigger, even though it produces a smaller image on your eye.

One theory about the moon illusion says that when the moon is near the horizon we perceive it to be farther away from us than when it is high in the sky. But since the moon is actually the same size, our minds make it look bigger when it is near the horizon to compensate for the increased distance.

One way that you can trick your mind out of the moon illusion is to bend over at the waist and look at the moon upside down through your legs.

An alternative explanation holds that the moon illusion is caused by the way our eyes focus on distant and close objects. When we focus on the horizon moon, we focus on the moon at a great distance. The overhead moon lacks visual cues that tell us how far away the moon is, so we focus on the moon as if it was a short distance away. See here for the details of this theory.

So, for now, the right answer is that there is no right answer. But the one thing people agree on is that the moon does not physically change its size or distance from Earth as it moves across the sky. It's all in our heads.

Here are some interesting links:

• ABC News article about moon illusion
• USA Today Astronomy Page
• Other Illusions
• Moon Will Appear Larger Than Normal
• Could I see a flashlight beam from Earth on the moon?

Edited November 9, 2010 by John Dolva

[Craig Lamson]

C'mon, Craig, I never claimed to have proven anything. I DEMONSTRATED why I believe the bags are not the same. Now you have countered this by saying that since we don't know EXACTLY how far the bag was from Montgomery and how far the cameras were from the bag we can never know for sure....

Do you even read the words you write? First, you will never be able to accuratly replicate the press photos, since you don't knwo thew distances involved and you can't measure from photo to photo...like you have incorrectly done... This has been proven time and time again but Pat Speer has decided the heck wiht established science and fact...he knows best. NOT!

This is malarkey. We know that, in order for a bag to appear 25% wider than its normal appearance against Montgomery, it would have to be significantly closer to the camera in comparison to Montgomery. You, as a photographer, are in a position to actually test this.

I DID test this PAt...as wall pat and stick Pat show. You rember them, dont you?

Let's start by agreeing on an outside parameter. Let's say, for example, that the bag was at most one foot from Montgomery. You can then set up something one foot in front of the other.

WHY? We would need to know the exact distance, to do what you suggest since the distance ratios are the obnly thig that matter. And we don't know the distance, and your one foot figure is simply a fabrication. So what is a number picked from thin air going to tell us about the press photo and your recreation?

We can then agree that the camera used by the press photographers had a 50mm lens.

Sheesh did you learn nothing at all throughout this exchange? FOCAL LENGTH MEANS NOTHING IN REGARDS TO PERSPECTIVE. A 50 mm lens, a 15mm lens, a 200mm lens a 500mm lens wil all produce the very same image perspective of a given scens provded the camera to subject DISTANCE remains the same. Did you get that...the lens does not produce perspective changes, its camera to subject DISTANCE.

You can then take pictures of these two objects--perhaps your rulers--starting at two feet from the closest object, and then working your way back, one foot at a time. Well, at what point will 4 inches on the closest ruler match 5 inches on the furthest ruler? I'm guessing it will be about 4 feet, far closer than at least two of the photos taken of Montgomery, in which the bag appears to be far wider than the bag in the archives.

Take a look at wall pat and stick pat. In one photo the camera was at 10 foot and stick pat was 3 inches away. The next photo has the camera at 7 foot and stick pat 13 inches away. The point HAS been proven, you just can't deal...honestly... with the answer. This is not rocket science Pat.

You, however, have been pretending that we just can't tell these things, and that 4 inches on the front ruler can appear to match 5 inches on the rear ruler, even from ten feet away or further. I've asked you to prove this. In your attempt to prove that an object can appear 25% wider than itself in two photos from ten feet or so, however, you turned the round light you were using to simulate the bag from the camera, to make it appear more narrow. You CHEATED.

I simply showed you one MORE way the size can change, I also gave you a number of OTHER examples using different methods. I'm really sorry that you can't understnad simpe demonstarions of principle. Thats is YOUR failing, not mine. BTW, I were you I would be quite hesitant to accuse someone of CHEATING considering the nature of your silly recreation compaired to the actual press photo. That was nothng but a fabrication. Pot meet Kettle.

You knew that the bag in my re-enactment, which appeared to be much narrower than the bag in the press photos, was NOT turned away from the camera, and yet you did it anyhow.

Sheeesh Pat, it had NOTHING to do with your recreation photo, or ANY other photo. It was a simple demonstration of how changes in position of an object in 3d space can effects it size in a 2d photograph. It was one of MANY such demonstrations I presented that all showed the same effects using different methods. It was designed to illustrate EXACTLY why your silly method of "measuring' objects in a photograph was faulty.

That you considered it an attempt to counter your fabricated recreation is just plain silly. I don't do "recreations' Pat, as I have stated many times over.

I take this as an acknowledgment that you are completely stumped as to how the bag could appear so wide in the press photos, and that you thereby concur with my analysis that the bags are not the same.

No you are the one who continue to be stumped. I know EXACTLY how it could look that way an have provided quite a few actual examples of how the process works. I use and observe this very process every working day. You on the other hand continue to fumble around ignorant of the simple principle of photograhic perspective. And now you want to drag others into your pit.....