http://www.forrestrace.com/china-focal/
Will somebody help me on this physics problem? EXTREMELY challenging?
I had 4 problems for hw and i did three of them and i cannot figure out this last one. it is so hard. anybody who can work this is a genius.
Imagine you are an astronaut on the moon photographing the earth with your Hasselblad camera whos f/2.8 lens has an 80-mm focal length. Is it possible (even in principle) for you to see the Great Wall of China (width 7.6m) on the photograph? If not, then what is the size of the smallest object that can be seen?
Please someone show me the steps and how to work this. I have been working on this for the past 2 hours and have gotten nowhere. Please help. Thanks!
The width of the image on the film is
Wf = [W/D]* f = [7.6/384E6]*.08 = 1.583E-9 m = 1.583E-6 mm
I doubt the film grain would be fine enough to register any image of this dimension, but you might check into it…….
It has been reported that the great wall can be seen from space, but these reports have assumed an urban legend status, as this paragraph from Wikipedia debunks:
The Great Wall is a maximum 9.1 m (30 ft) wide and is about the same color as the soil surrounding it. Based on the optics of resolving power (distance versus the width of the iris: a few millimetres for the human eye, metres for large telescopes) only an object of reasonable contrast to its surroundings 70 miles or more in diameter (1 arc-minute) would be visible to the unaided eye from the moon, whose average distance from Earth is 384,393 km (238,857 miles). The apparent width of the Great Wall from the moon is the same as that of a human hair viewed from 2 miles away. To see the wall from the moon would require spatial resolution 17,000 times better than normal (20/20) vision.[11] Unsurprisingly, no lunar astronaut has ever claimed seeing the Great Wall from the moon.
A more controversial question is whether the Wall is visible from low earth orbit, i.e., an altitude of as little as 100 miles (160 km). NASA claims that it is barely visible, and only under nearly perfect conditions; it is no more conspicuous than many other man-made objects.[12] Other authors have argued that due to limitations of the optics of the eye and the spacing of photoreceptors on the retina, it is impossible to see the wall with the naked eye, even from low orbit, and would require visual acuity of 20/3 (7.7 times better than normal).[11]
MVRDV China Comic & Animation Museum (Animation by Wieland & Gouwens)
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