Hi all,

I'm working on a 3D model f the Earth and Mon, with a few other objects. I run into what seems a difficult issue ... the size of the moon.

I my scene I have placed a scale Earth and scale moon placed a scale distant apart. The moon is WAY to small.

In my scale one unit is equal to 500km; my Earth's radius is 13 units (a tad large), the moon at 3.5 units is placed 700 units from Earth. When I place a camera in "Eath orbit" (about 360km altitude) and pint it at the moon, it is so small that it is hardly visible. I checked and rechecked my scale, and all seems correct. I've even lace a model of ISS in the scene as a sort of reference since I can find photographs of ISS and the Moon. With ISS properly scaled, and the camera positioned about 20km away from ISS, the Moon is virtually lost behind the station.

Now its not like I can't fix it, I can always increase the size of the mon, ad sice the animation I want to build doesn't require I go near the Moon, it shouldn't be hard to make it "look" good, but, I will know that my Moon is way to large (I have to make the moon larger than Earth for the "illusion" to work).

So I'm wondering if anyone can tell me what might be happening here, what am I doing wrong? I ean, I always thought that scale and perspective work, but as I can now see .. not always.

Thanks.

Originally posted by AnthraAndromda
my Earth's radius is 13 units (a tad large), the on at 3.5 units is placed 700 units from Earth.

Its probably correct. The moon is smaller than it "appears" to be.
Your value of the moon being 27 earth diameters away is much the same as what I get checking other sources, and it being only 0.27 the size of the earth also matches what I find.

... it is so small that it is hardly visible.

Again, much the same as what you get if you have a REAL camera on earth and take a photo of the moon.
Try it yourself. Without a telescope, it really is just a tiny dot.

I am not understanding where you got your scales. Just popping out the calculator real quick, and looking up the sizes and distances involved, what I got for a 500 Km scale is as follows:

Diameter of Earth = 25 units
Diameter of Moon = 7 units
Distance between E and M = 714 units

IMO you would do better to use a larger scale. I could be making a mistake here, but that is what I got anyway.

If your Earth is 15 units, then that multiplied by 0.38 should give a moon size of approx. 5.7 units. The distance between them would then be 25.6 of your Earth-diameters--that is, approx. 384 units.

Does that match your math?

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ETA: Oops... While I was doing my calculations, JiggyPotamus weighed in with a different answer. Do I need to check my calcs, Jiggy, or do you?

Oh, wait. Your earth is 13 units? Hold on....

Originally posted by JiggyPotamus
I am not understanding where you got your scales. Just popping out the calculator real quick, and looking up the sizes and distances involved, what I got for a 500 Km scale is as follows

Diameter of Earth = 25 units
Diameter of Moon = 7 units
Distance between E and M = 714 units

IMO you would do better to use a larger scale. I could be making a mistake here, but that is what I got anyway.

Actually your math agreen rather well with mine. I too looked up the sizes of these two bodies.

My Earth radius 13 units or diameter = 26 (as I said a bit large)
My moon radius is 3.55, so about a diameter of 7units.
My distance is 700 units (center to center) So they are a bit close.

Increasing the scale ... may yet happen, I've already done that once, when I add ISS and the Shuttle. Ma are they SMALL!

perspective(?) :
A 50mm lens gives a "normal" perspective to a 35mm film ( or "full frame" digital camera). The "normal lens" changes with the diagonal of the sensor or film size.A "wide angle" ( shorterthan 50mm) will make it look smaller in perspective. 80-mm is normal for medium format 150mm for a 4"x5";300mm iirc for an 8"x10" view camera.

Sorry. Wife called and I was sidetracked for a few minutes.

Anyway: If your Earth is 13 units, then that multiplied by 0.38 (Moon's size in relation to Earth), should give a moon size of approx. 5 units. The distance between them would then be 30 of your Earth-diameters--that is, approx. 390 units.

ETA: Well, the math is right; but I now notice you are using radii instead of diameters. Still.....

It's off topic some, but I have to say it. Claim the moon is normal size compared to the earth and the distortion is due to Nibiru.

i also think that all the pictures we see from the moon looking back at earth,seem strange.
because the earth looks the size of the moon..i would of thought that the earth would fill the field of view...
could be wrong,just my thoughts..
interesting thread.

It's all about the field-of-view of the camera. FOr example, a Canon 5D Mark II with a 105mm lense will have an FOV of ~19.5 degrees. The angular diameter of the Moon as seen from the Earth (and your model-moon seen from your model earth) is only half a degree, so the image of the Moon in a photo would be 1/39th the width of the picture frame. With a wide angle lense it would be even smaller. If you put a 200mm telephoto lense on that camera, the FOV would be 10 degrees, and the Moons image would be 1/20th the width of the frame.

Hope this helps.

Thank you, thank you, One and ALL!

You have helped to raise my level of knowledge and understanding of photography and cameras.

It appears that I did have my scale correct, but need to learn to control the camera options I have available.

46Ace, Saint, wmd; I don't know whether to find you and shake your hand (and buy ya a beer), or punch ya on the nose. Cause of you I get to "hit the books" , well okay, read the f*ing manual, and find out just how well cameras have been implemented in this software I have. Don't suppose any of you know anything about "Poser" do ya?

Well, I'm off to learn about adjusting FOV and other fun things.
Thanks again y'all

Okay, I wat to thank y'all again for the help in ubderstanding. Seems to me that IF the whle wrld could work at this kind and degree of cooperation, well...this would a far, far better place.

Anyway, here is a somewhat size reduced image of what I think I'm looking for...





Next I need to get my textures together, and lighting, but, your help has been awesome!

Oh, and for those who are a bit more casual to this thread ... there is nothing real in this image, only 3D models of real objects, and no, they aren't arranged in any configuration that might occur naturally (but, then; who knows".