Drones the size of cars??

[roger1440]

Drones the size of cars?? How does a person estimate the size of a drone when there is nothing to use as a point of reference? If I saw a drone near a person I can estimate the size of the drone based on the size of the person. The only thing that would throw me off would be if the person was unusually tall or short. But if the drone was the only thing in the sky there would be no way to tell the size. How big is this thing in the picture? Can you tell what it is?

 

[jonnyH]

@roger1440

Grains of salt on MDF? So very small, a few tenths of a millimetre?

 

[FatPhil]

With the filename tiny_salt.jpg, I'm guessing it's salt and it's tiny.

 

[MonkeeSage]

Looks like micrometers

With the filename tiny_salt.jpg, I'm guessing it's salt and it's tiny.

 

[Ann K]

@roger1440
This is a problem we run into a lot. Witnesses to an object or event estimate the size or the distance or the speed, but if they do not know those for certain, all bets are off as to their accuracy. If speed is estimated to be outside the known limitations of physics, we look for mistakes before we try to rewrite physics. If it's an unfamiliar object, a nearby butterfly or beetle can be (and has been) mistaken for a distant UFO. We've had long discussions about, for example, whether pilots can be called "trained observers". I think the consensus is that yes, they are when identifying aircraft (which they're trained on) but are no more likely to be correct than the average man in the street if dealing with an unknown object.

 

[roger1440]

Looks like micrometers

With the filename tiny_salt.jpg, I'm guessing it's salt and it's tiny.

That was put there deliberately to throw people off. Much like flying saucers disguised as drones.

 

[LeastWeasel]

@roger1440
This is a problem we run into a lot. Witnesses to an object or event estimate the size or the distance or the speed, but if they do not know those for certain, all bets are off as to their accuracy. If speed is estimated to be outside the known limitations of physics, we look for mistakes before we try to rewrite physics. If it's an unfamiliar object, a nearby butterfly or beetle can be (and has been) mistaken for a distant UFO. We've had long discussions about, for example, whether pilots can be called "trained observers". I think the consensus is that yes, they are when identifying aircraft (which they're trained on) but are no more likely to be correct than the average man in the street if dealing with an unknown object.

Exactly - when former MD governor says "drones flying over his house" and shows video of distant lights in the sky.

 

[captancourgette]

chunks of ice on your crotch

 

[roger1440]

An example of lens compression. Lens compression is when the background elements of a picture appear larger then what they actually are. The higher the focal length of a lens the greater the lens compression. Lens compression is more appropriately referred to as perspective distortion. It is not a defect in the lens.

The first picture is taken with a lens set at 23mm. The camera sensor is one foot from the left bottle, two feet from the middle bottle and three feet from the right bottle. The second picture was taken with a lens set at 230mm. The camera is backed up to recompose the picture to get the left bottle the same size as the left bottle in the first picture. Nothing on the table was moved. Note how the middle bottle and the right bottle appear to be larger.

I use lens compression to my advantage with my food photography. I'm working with a small fold up table. By using a lens with a long focal length the edges of the table will be out of view of the camera. Working with lens compression can also be used as a nifty trick for cityscapes. I can take a portrait of someone with the Manhattan skyline behind them. The skyscrapers behind the person can be large or small, depending on the focal length of the lens.

What does this have to do with the size of drones? A lot. Just by changing the focal length of a lens can change perceived size of a drone. Example: Let's say the Ginger bottle was a person. The Paprika bottle or the Tarragon bottle was a drone. Just by switching the lens the drone would now appear larger or smaller.

Last night I read a post from a Facebook Group. A woman mentioned she viewed a drone through binoculars. She said the drone was very large.

 

[Mendel]

The camera is backed up

That is the true cause of "lens compression" (also called perspective compression). Take a picture with the 23mm lens from that position and crop/enlarge it, it'll look the same proportion-wise as the uncropped 230mm picture from the same position.

If you view the picture from the proper distance that replicates the camera FOV, it won't appear "compressed"—the phenomenon is caused because our viewing angle much exceeds the camera FOV when the picture was taken. (We have had a similar, opposite problem with a wide-angle picture before.)

 

[roger1440]

That is the cause of "lens compression" (also called perspective compression). Take a pucture with the 23mm lens from that position and crop it, it'll look the same proportion-wise as the uncropped 230mm picture from the same position.

Yes, I know.

 

[FatPhil]

The first picture is taken with a lens set at 23mm. The camera sensor is one foot from the left bottle, two feet from the middle bottle and three feet from the right bottle. The second picture was taken with a lens set at 230mm. The camera is backed up to recompose the picture to get the left bottle the same size as the left bottle in the first picture. Nothing on the table was moved. Note how the middle bottle and the right bottle appear to be larger.
...
What does this have to do with the size of drones? A lot. Just by changing the focal length of a lens can change perceived size of a drone. Example: Let's say the Ginger bottle was a person. The Paprika bottle or the Tarragon bottle was a drone. Just by switching the lens the drone would now appear larger or smaller.

"just by switching the lens" is contradicted by "The camera is backed up to recompose the picture".

 

[roger1440]

(We have had a similar, opposite problem with a wide-angle picture before.)

Shot with the Sigma 10-20mm lens set at 10mm

 

[Mendel]

Shot with the Sigma 10-20mm lens set at 10mm

creating more perceived depth and size difference for the tomatoes

 

[Jack Mallory]

How big is this thing in the picture?

If I had to guess?

 

[roger1440]

"just by switching the lens" is contradicted by "The camera is backed up to recompose the picture".

Yeah, I should have left out the word "just". I wrote this for a few Facebook Photography Groups I belong to long before the epidemic of the New Jersey drone migration. I had another post explaining the math behind it but can't find it.

 

[roger1440]

Maybe I should have gone into more detail with the math behind it. If I were to take a picture of a man and woman standing side by side who were the same height and equal distance from the camera they would appear to be the same height from the camera's perspective. In this example a 50mm lens is being used. The man and woman are 10 ft. from the camera. A second picture is taken using the same lens. This time the woman backs up 10 ft. The man is still 10 ft. from the camera but now the woman is 20 ft. from the camera. The woman now appears to be half the height of the man from the camera's perspective because she is double the distance from the camera compared to the man. A third picture is taken. This time a 100mm lens will be used. In order to get the man the same size as he was in the second picture the camera is backed up 10 ft. The man is now 20 ft. from the camera and the woman is 30 ft. from the camera. The man is now 2/3 the distance from the camera compared to the woman. From the camera's perspective the woman is now 2/3 the height of the man. Compared to the second picture she grew. She grew not because of the focal length of the lens. She grew because of the distance she was from the camera compared to the distance the man was from the camera. In the second picture she is twice the distance from the camera compared to the man. In the third picture she is only 1.5 times the distance from the camera compared to the man. Think of it as a ratio.

 

[Mendel]

She grew not because of the focal length of the lens. She grew because of the distance she was from the camera compared to the distance the man was from the camera.

Yes. Which is why I like to call this perspective compression.

 

[roger1440]

Yes. Which is why I like to call this perspective compression.

The point I'm making if someone views these drones with a telephoto lens or binoculars they may appear larger than they are. Here is an example. A person sees a drone over there neighbor's house. This person gets there binoculars to get a better view. The drone now appears larger, maybe the size of a car or SUV. In reality it's just your garden variety plane in the distance. This change in perspective goes by several names.

 

[jarlrmai]

There's no such thing as lens compression it's all down to distance to subject.

 

[roger1440]

There's no such thing as lens compression it's all down to distance to subject.

I explained in detail what I mean. If you can explain it better, please do and post it.

 

[jarlrmai]

Take an image at 200mm then don't move the camera, change the lens to 24mm then crop the 24mm image to the same FOV as the 200mm the 2 images will look the same just one will be lower res. The way objects look in a photo has to do with perspective from the distance the camera is away, not the focal length of the lens.

https://mastinlabs.com/blogs/photoism/the-truth-about-lens-compression

 

[Mendel]

The point I'm making if someone views these drones with a telephoto lens or binoculars they may appear larger than they are. Here is an example. A person sees a drone over there neighbor's house. This person gets there binoculars to get a better view. The drone now appears larger, maybe the size of a car or SUV. In reality it's just your garden variety plane in the distance. This change in perspective goes by several names.

You explained perspective compression as a relation: "She grew because of the distance she was from the camera compared to the distance the man was from the camera." When you see the object by itself, there is no comparison. Your claim then boils down to "objects seem larger when viewed through binoculars", and they would seem smaller when you reverse them. Most people realize this.

The problem we are facing here is that people misjudge the distance, because they have been primed to see a drone at a few hundred feet when they actually see an aircraft at a few miles, and thus they inevitably misjudge the size.

 

[roger1440]

When you see the object by itself, there is no comparison.

I know. That was my starting point. I read this article over four years ago. Took me a while to find it. https://www.theguardian.com/austral...-of-crowded-beaches-may-not-be-what-they-seem

 

[Mendel]

I know. That was my starting point. I read this article over four years ago. Took me a while to find it. https://www.theguardian.com/austral...-of-crowded-beaches-may-not-be-what-they-seem

See also https://www.metabunk.org/threads/covid-19-coronavirus-current-events.11085/page-10#post-238748

 

[roger1440]

 

[jarlrmai]

Again the reality of why things are is important here, it's a rule of thumb for new photographers to say use a long lens for this effect, because it's implied that they will always fill the frame.

But for a this kind of forum it's really important to know that it's not the focal length that causes it, it's the distance from the subject, the long focal length just allows the frame to be filled with the subject that distance.

 

[Trailblazer]

Again the reality of why things are is important here, it's a rule of thumb for new photographers to say use a long lens for this effect, because it's implied that they will always fill the frame.

But for a this kind of forum it's really important to know that it's not the focal length that causes it, it's the distance from the subject, the long focal length just allows the frame to be filled with the subject that distance.

Yes: the reason for the "perspective compression" is not the lens, it is the ratio of distances between objects. (This is essentially what you are saying, @jarlrmai)

In the example of the spice jars, with a wide angle lens the camera is the same distance from Jar 1 as Jar 2 is from Jar 1.

Both distances are 1ft, so with the wide angle lens jar 2 is 2x further away than Jar 1 and therefore appears half as tall (ratio 1:2).

Using a longer lens necessitates putting more distance between the camera and the first jar, to make the first jar appear the same size in the frame.

With the telephoto lens, the camera might be 10ft from Jar 1, but Jar 2 is still only 1ft from Jar 1.

That means Jar 1 is now 10ft away and Jar 2 is now 11ft away. With the telephoto lens, jar 2 is 1.1x further away and will therefore now appear 10/11ths as tall as Jar 1 (ratio 1:1.1).

So it is not the lens "distorting things" - it is simply that telephoto lenses are usually used to take photos of things that are further from the camera, so the distances between the things themselves will be smaller, relatively speaking.

 

[Trailblazer]

There are really two separate issues at play here.

First if all, just looking at something through binoculars or a telephoto lens will make it look bigger, because the lens physically magnifies the image.

But second, looking through a telescope or a long lens at a distant object when there are also other more nearby objects within the frame can give a distorted impression of size.

The classic example is telephoto shots of the moon. Here is an extreme example, which is a screenshot from a video.

Using lens compression to capture a giant moon is nothing new, but photographer Daniel López has taken things to a whole level. He set up an ultra-telephoto lens about 10 miles (16km) away from a volcano and captured this mind-blowing 2-minute video that shows a moonset in real-time.

López shot the footage near Mount Teide in the Canary Islands off the coast of Africa. He used a giant telescopic lens, Canon teleconverters, and a Sony a6300 camera.
Source: https://petapixel.com/2018/06/05/this-is-what-a-moonset-looks-like-with-an-ultra-telephoto-lens/

So here, the moon is 230,000 miles away and the people on top of the volcano are 10 miles away.

Ratio is 10 miles to 230,000 miles = 1:23,000.

Whereas in a photo like this with a wide-angle lens, the person might be (at a guess) only six feet away, but the moon is still 230,000 miles away.

Ratio is now 6 feet to 230,000 miles = 1:202,400,000

So the moon will appear 202,400,000 / 23,000 = 8,800 times bigger in the telephoto image than in the wide-angle image, relative to the people. Obviously in this case the people are also smaller in the frame, so the moon size itself will be proportionally slightly less enormous, but if you blew it up even more so the people were as tall as the person in the portrait, that's how much bigger it would be.

 

[Mendel]

But second, looking through a telescope or a long lens at a distant object when there are also other more nearby objects within the frame can give a distorted impression of size.

... continues to give an example where the telephoto gives a better impression of its size...

 

[Trailblazer]

... continues to give an example where the telephoto gives a better impression of its size...

Good point... perhaps a better description would be "distorted compared to our normal impression of how something looks"? I mean, we know the moon is big, but we also know that it is visually a small thing in the sky.

Similarly, we know planes are big (compared to, say, a house or a person), but we also know that usually when we see them in the sky they look small. But with a telephoto lens and something on the ground to compare them to, that is not necessarily so...

(Photo source)


To be honest though I think with most of these "drone sightings" we have the opposite problem: people are seeing large planes a long way away and thinking they are small drones nearby.

 

[FatPhil]

There's no such thing as lens compression it's all down to distance to subject.

I'd go further and say it's down to *relative* distances to both the object whose size is under question and a reference object you're trying to make a comparison to. So the spice jar example was 1:2:3 (big difference) vs. 10:11:12 (bugger all difference) if I've remembered the numbers correctly.
If there is no reference object, almost no evaluation is possible, and you're tricking yourself if you think you can estimate the size. There may be other clues that you think help you, but if you don't know the depth of field, or whether the tiny salty cameraman was using a tilt-shift lens to deliberately fool you, you're just guessing. (For those not familiar with tilt/shift, a special lens is used that modifies the focal plane and makes real world objects/situations look like cute little model villages, it's very effective an illlusion even if you know it's being done.)

Also note that you need 2 known distances to perform a size comparison. We don't even have this in the drone case.

 

[Ann K]

I'd go further and say it's down to *relative* distances to both the object whose size is under question and a reference object you're trying to make a comparison to.

Every artist knows that. Every person knows that, when dealing with comparisons of familiar objects. Nobody is going to look at a view like this and think "Wow, that tree is as big as the mountain!" It's the unfamiliarity (in their minds) of the object, made more "mysterious" by the darkness and lack of comparisons.

 

[roger1440]

Every artist knows that. Every person knows that, when dealing with comparisons of familiar objects. Nobody is going to look at a view like this and think "Wow, that tree is as big as the mountain!" It's the unfamiliarity (in their minds) of the object, made more "mysterious" by the darkness and lack of comparisons.
View attachment 74799

But what happens when we use unfamiliar objects and unknown distance between objects? This picture is from the movie "Attack of the 50 Ft. Woman" (1993). No CGI or paintings were used. It's just simple forced perspective. If we were to replace the woman with a small drone we end up with a 50 foot drone. If we play around with some of the numbers we could end up with a drone the size of a car or SUV.
Source: https://www.youtube.com/watch?v=HOsoT-jrHcQ