FAR SIDE OF THE MOON

[bknight]

I speak spanish.
For anyone wondering, Ill traduce what he said the best I can:
Your drawing is simplistic and wrong: the moon is at a distance 30 times the diameter of the earth, while in the drawing, is just 10 times... and you will notice that the farther away the moon is from the earth in this drawing, a bigger proportion of the earth is covered by the moon, because of that reason the moon would never be seen of less size when it is on the first plane.
If you are an Apollo astronaut and you see the earth from the known face, you drive the imaginary rover capable of carry you on to the farside of the moon. Once you are in the opposite side of the moon from where you landed, you get inside a rocket and you fly away in a straight line... you would never see the earth, because it will be covered for ever by the moon. The same happens with the satellite, a real transit of the moon infront of the earth must necessarily show the moon much more bigger than the earth.
It has been registered some transits of the moon with planets like jupiter, you cannot make jupiter be seen with a bigger size when jupiter is obviously much bigger than the moon, the same example applies in the Earth-Moon scenario.

Using your translation and I'm not sure this is fair, but tarkus this is exactly backwards as the view from the Mars image proves.

[sts60]

Tarkus, the problem isn't your English; it's quite serviceable.  The problem is your complete failure to grasp elementary trigonometry, and as has been already pointed out, your confusing of basic aspects such as focus and focal length.

But your biggest problem is your stubborn refusal to learn anything.  You literally have no idea what you're talking about, and yet you keep dismissing actual experts when they try to help you.  Even more distressing, understanding this doesn't require real expertise; you can observe the same principle in everyday life, and the math involved is grade-school stuff.

[smartcooky]

Make a small effort, go and read something about astrophotography ... you'll find out the use of a symbol on some cameras, looks good:



You can not do these tricks when you look at planets or very distant objects, when you focus to infinity no way to make background objects look larger. To understand what ought to read or practice ... either stop beating around the bush and admit that your argument is wrong.

I have been doing astrophotography on and off for about 40 years. I am also a photographer by trade and have my own darkroom and digital printing business.

You are making the fundamental error of confusing focal distance with focal length.

Focal distance is the distance from the lens to the object being observed.  Its IN FRONT of the lens.

Focal length is the distance from the lens back to the focal point or plane. Its BEHIND the lens.

The ∞ symbol is used to set the "depth of field" on a camera; that is the range over which everything in the field of view is "in focus". By setting the ∞ symbol opposite the f-stop (f) figure, you can read the depth of field off the other f-stop figure



In this example the ∞ symbol is dialled to a point opposite f16 on one side of the centre mark. You then look at the distance number opposite the  f16 on the other side of the centre mark, and this will tell you that when the camera lens is set to f16, everything from ∞ to just under 0.4m (1.2 ft) away from the lens will be "in focus" i.e. sharp.

Having read through what I have just written, I think I might understand your confusion. The ∞ symbol on a camera is not used for anything other than to get close up objects in a field to appear in focus along with far away objects. NOTE: that is close up physically, NOT relatively. DEPTH OF FIELD will not work at astronomcal distances because those distance are too large, but this has NOTHING to do with the relative sizes of objects in the field.

[Cat Not Included]

The entire "moon will always block the Earth" argument could be readily tested with some cheap supplies (two Styrofoam spheres, one approximately four times the size of the other) and two wooden dowels), a basic camera, and probably less than 20 minutes of effort.

Set up the spheres side by side with the center at the same height, start the camera right next to the small sphere, and move the camera away. See how the image changes.

[JayUtah]

The entire "moon will always block the Earth" argument could be readily tested...

Agreed, but tarkus simply sidesteps all those invitations to stage his own demonstrations by asserting than nothing we can do on Earth proves anything about astronomical objects and distances.  It's a cargo-cult appeal to magic.

[Cat Not Included]

The entire "moon will always block the Earth" argument could be readily tested...

Agreed, but tarkus simply sidesteps all those invitations to stage his own demonstrations by asserting than nothing we can do on Earth proves anything about astronomical objects and distances.  It's a cargo-cult appeal to magic.

Yep.
One of Tarkus' premises seems to be that if you make the numbers big, the fundamental nature of math changes.

[JayUtah]

I think he's confused by our use of "focal length" and field of view, which he assumes means focus distance.  That's why he referred to the infinity symbol as a lens setting.  Astronomical photography can be done via normal lenses with the focus setting at infinity, and it appears tarkus (wrongly) believes that things we point to that are affected by focal length (i.e., the effects of foreshortened foreground/background relationships) cannot thereby be manipulated with an infinity focus distance.  As many have noted, he's conflating similarly named but dissimilar concepts in optics.

[Abaddon]

I think he's confused by our use of "focal length" and field of view, which he assumes means focus distance.  That's why he referred to the infinity symbol as a lens setting.  Astronomical photography can be done via normal lenses with the focus setting at infinity, and it appears tarkus (wrongly) believes that things we point to that are affected by focal length (i.e., the effects of foreshortened foreground/background relationships) cannot thereby be manipulated with an infinity focus distance.  As many have noted, he's conflating similarly named but dissimilar concepts in optics.

I think it is much more simple. Tarkus thinks that local "up" is universal and all cameras must perforce have the same orientation wherever they are in space. Sure, you can rotate your camera on the ground, but in space that is verbotten for reasons which he declines to specify.

[nomuse]

Meh.

Unless my brain has gone to porridge what with these hot days we've been having, lens length is only material in how wide the field of view is. It matters for "Earth should look bigger" (that is, take up more of the frame in some photograph in question) but not for any comparison of visual diameters. Aka "The Moon should look bigger than the Earth."

For that question, it is only about location, location, location. Camera matters not. It's all in the geometry.

Which is why I must repeat; from the distance of Earth, Jupiter's larger moons are clearly incapable of covering Jupiter. So, Tarkus, will you admit that there exists a distance -- one smaller than infinity -- at which the Moon will be visually smaller than the Earth?

[JayUtah]

Unless my brain has gone to porridge what with these hot days we've been having, lens length is only material in how wide the field of view is. It matters for "Earth should look bigger" (that is, take up more of the frame in some photograph in question) but not for any comparison of visual diameters. Aka "The Moon should look bigger than the Earth."

It's the combination of camera position and focal length.  The dolly zoom manipulates both, usually with the goal of maintaining the foreground object at the same size in the frame.  This results in a shift in the perception of distance between foreground and background elements, best described as expanding or compressing the apparent depth in the scene.

[nomuse]

Yah, but does not the dolly zoom trick require, well, the dolly?

If Tarkus is directly comparing apparent diameter of Moon and Earth without consideration of the frame, that is purely a matter of the distance the photograph was made from.

[Jason Thompson]

do not forget that Moon is about 400,000 km away and it looks like a small sphere of only about 2 degrees from the moon Earth

Correct, Earth appears 2 degrees across from the Moon, 400,000 km away. So how big will Earth appear to be from double that distance?

[onebigmonkey]

Here's a Stellarium animation I did for elsewhere on the interwebz:



Tarkus, is this astronomy software lying to me?

[Paul]

Meh.

Unless my brain has gone to porridge what with these hot days we've been having, lens length is only material in how wide the field of view is. It matters for "Earth should look bigger" (that is, take up more of the frame in some photograph in question) but not for any comparison of visual diameters. Aka "The Moon should look bigger than the Earth."

For that question, it is only about location, location, location. Camera matters not. It's all in the geometry.

Hi nomuse, yes you are right, if we are just considering relative sizes then cameras and focal lengths and focal points are not relevant.  You just need to compare Moon/Earth size ratios and relative distances to observer as I did in a couple of earlier posts and others have done in diagrams and photos.

To confirm 'in the field' the effect of focal length on relative size I went out this morning and shot the following:

70mm focal length, with the 'Moon' (small ruler) one metre from the 'Earth' (the big ruler).  The camera is positioned 6 metres further on from the 'Moon'. The relative distances match the Earth/Moon/DSCOVR positions



Using 10cm on the small ruler for the Moon diameter and 40cm on the big ruler for the Earth (sizes chosen to keep things simple) and after resizing and cropping to an image width of 1000 pixels we get:
Moon (168px) / Earth (498px) = Moon/Earth ratio of 0.337 = 33.7%.

Now at 100mm focal length (all objects and the camera unmoved):


Moon (152px) / Earth (454px) = Moon/Earth ratio of 0.335 = 33.5%.

200mm:


Moon (162px) / Earth (484px) = Moon/Earth ratio of 0.335 = 33.5%.

And finally 300mm:


Moon (236px) / Earth (710px) = Moon/Earth ratio of 0.332 = 33.2%.

Conclusion 1: So allowing for lens distortion through the zoom range, and margin of error from measuring the pixel lengths, the Moon and Earth ratio has remained constant regardless of focal length.

Now the effect of moving the camera forwards. We already have the 6m ratio at around 33% regardless of focal length.
So with camera at 3m from the Moon (at 70mm focal length):



Moon (171px) / Earth (423px) = Moon/Earth ratio of 0.404 = 40.4%.
So Moon has increased in size relative to Earth by moving nearer.

And with camera at 1m from the Moon (70mm):



Moon (353px) / Earth (473px) = Moon/Earth ratio of 0.746 = 74.6%.
The Moon has again increased substantially relative to the Earth.

Conclusion 2: Changing the relative distances between objects and observer changes the relative size of the objects.

[nomuse]

Which adds one more to my list of hoax beliefs that can be overturned with a straight-edge.