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Inverse Square Law, Sunny 16 On Earth, Sunny 8 On Mars???

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JohnSil

JohnSil

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Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL

Lets talk about the Inverse Square Law(ISL). I think most photographers don't know what the ISL is and why it's important or how it can benefit them.

Remember the photo threat a month ago about lighting the shoe? Some thought it could be shot with one light. Most Studio shooters know that the light falls off. If the light is correct on the subject then it's impossible to be correct at the background because of the ISL.

Here's a chance for all of you light engineers to shine a light on this subject!

What is the ISL and how can we use it to benefit from this knowledge in our every day photography?

But here's a hint, if it's Sunny 16 anywhere on Earth, will it be Sunny 8 on Mars?

John
 
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL

Lets talk about the Inverse Square Law(ISL). I think most photographers don't know what the ISL is and why it's important or how it can benefit them.

Remember the photo threat a month ago about lighting the shoe? Some thought it could be shot with one light. Most Studio shooters know that the light falls off. If the light is correct on the subject then it's impossible to be correct at the background because of the ISL.

Here's a chance for all of you light engineers to shine a light on this subject!

What is the ISL and how can we use it to benefit from this knowledge in our every day photography?

But here's a hint, if it's Sunny 16 anywhere on Earth, will it be Sunny 8 on Mars?

John
Click to expand...
I don't know about mars but the distance does not enter in the equation, it depends on the luminance of Mars.

Edit: it depends on the distance between the sun and mars, sorry my bad. I was more referring to the fact that a subject with a given luminance will be seen with the same intensity whatever the distance is.
 
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I don’t know about Mars but when I take photos of the Moon from Earth I use fill flash with the onboard unit to help lighten the shadows on it’s craters. I learned this in my home on the planet Zarg.
 
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I did not know the average distance of mars from the sun. So I reverse engineered your sunny 16 versus sunny 8 guideline to find out. Then I Googled the actual answer and discovered your guideline has a 30% error in the average position of mars relative the the light source of the sun.

F/8 would represent an accommodation to match 1/4 the light intensity that calls for f/16. But it appears that the actual average position of mars from the sun would call for about 43% as much sunlight intensity reaching that planet. So it appears to me that f/8 on mars would be somewhat more brightly exposed that f/16 on earth.

Of course, the inverse square law only factors in the difference in the sun's light intensity due to distance from that source. Perhaps you also factored in differences in atmospheric density which might affect the light actually reaching the surface. You could be right if the atmosphere of mars blocks more light than does earth's.
 
Doug Haag said:
I did not know the average distance of mars from the sun. So I reverse engineered your sunny 16 versus sunny 8 guideline to find out. Then I Googled the actual answer and discovered your guideline has a 30% error in the average position of mars relative the the light source of the sun.

F/8 would represent an accommodation to match 1/4 the light intensity that calls for f/16. But it appears that the actual average position of mars from the sun would call for about 43% as much sunlight intensity reaching that planet. So it appears to me that f/8 on mars would be somewhat more brightly exposed that f/16 on earth.

Of course, the inverse square law only factors in the difference in the sun's light intensity due to distance from that source. Perhaps you also factored in differences in atmospheric density which might affect the light actually reaching the surface. You could be right if the atmosphere of mars blocks more light than does earth's.
Click to expand...
I just couldn't get this problem out of my head. So I did some calculations.

If the light intensity calling for one aperture on earth and a different one on mars is only affected by the two planets' different distances from the light source (the sun) I calculate that sunny 16 on earth would be sunny f/10.5 on mars.
 
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL
Click to expand...
Mars is 134 million miles from the Sun. The earth is 93 million.

Your gut should tell you that ratio is close to sqrt(2j so the inverse square law would put it right around one full stop, not two.
JohnSil said:
Lets talk about the Inverse Square Law(ISL). I think most photographers don't know what the ISL is and why it's important or how it can benefit them.

Remember the photo threat a month ago about lighting the shoe?
Click to expand...
You threatened to light someone's shoe?

Were they wearing it at the time?
 
Mars is easy, it's one of our closest neighbors. And like mentioned above, it's more like f/11 than f/8. There is pretty much no atmosphere so the contrast will be more extreme than on earth but not quite as bad as on the moon, which was handled relatively well with film 50 years ago.

What's more interesting is pluto. Pluto's orbit is rather eccentric so the distance to the sun can be between 30 and 49 astronomical units. (Those being 150 million km, the distance from the earth to the sun.)

So that means that on pluto the light is between 1/900th and 1/2400th of the light here on earth, or about 10 or 11 stops. So rather than f/16, ISO 100, 1/125 on earth, you'd have to use something like f/11, ISO 800 and 1/2.

The New Horizons cameras have apertures between f/8.7 and f/12.6, no info about ISO. Also note that for these planet exploring spacecraft it's common to have monochromatic sensors that are exposed with different color filters one at a time to get color images.

BTW, what I've always wondered about is how those space cameras do their focusing.

A while ago we had a disagreement about whether sunny 16 always applies regardless of how far above the horizon the sun is. My take, partially from living at 52 degrees north, is that this does make a difference.
 
Joseph S Wisniewski said:
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL
Click to expand...
Mars is 134 million miles from the Sun. The earth is 93 million.

Your gut should tell you that ratio is close to sqrt(2j so the inverse square law would put it right around one full stop, not two.
Click to expand...
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
 
I just use my iPhone on Mars and not bother with setting exposures manually.
 
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JohnSil said:
What is the ISL
Click to expand...
It's this: https://en.wikipedia.org/wiki/Inverse-square_law
JohnSil said:
and how can we use it to benefit from this knowledge in our every day photography?
Click to expand...
By understanding that the intensity (or illuminance or irradiance) of light or other linear waves radiating from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source, so an object (of the same size) twice as far away receives only one-quarter the energy (in the same time period).

And not being taken by surprise when it proves true.
JohnSil said:
But here's a hint, if it's Sunny 16 anywhere on Earth, will it be Sunny 8 on Mars?
Click to expand...
Apparently not. But I guess your hint is to indicate that when a light source is moved farther away its illuminating effect is reduced. Yep, it's true.
 
bobn2 said:
Joseph S Wisniewski said:
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL
Click to expand...
Mars is 134 million miles from the Sun. The earth is 93 million.

Your gut should tell you that ratio is close to sqrt(2j so the inverse square law would put it right around one full stop, not two.
Click to expand...
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
Click to expand...
The average scene reflectivity (albedo) on Mars is always the same as that on Mars.

But… if you're trying to talk about the scene difference between Mars and Earth, remember it's not about the average albedo, but about the scene reflectivity in certain "zones" or for certain subjects, so "sunny 11" on Mars should work like "sunny 16" on Earth if you're trying to shoot pictures of scenery, your friends, the natives, the painted boats on the canals, etc.

"Loony 11" works when you're taking pictures of the moon because the moon is really pretty dark, it’s albedo is only 12%, but we want to give the impression of a higher than normal albedo: we want it to look brighter than the dull grey of properly exposed. Toss in your friends, the grandstands at the racetrack, a few colorful moon-buggies, the moon burger stand, the Hard Rock Cafe - Tranquility, and you're right back up to "sunny 16".
 
bobn2 said:
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
Click to expand...
Actually, the "average scene reflectivity on Mars" is often "the same as that on Mars"... but possibly not the same as that on Earth...;-)

Of course, if a close up shot is too dark you can ask a Martian to hold your flash for you.
 
iljitsch said:
Mars is easy, it's one of our closest neighbors. And like mentioned above, it's more like f/11 than f/8. There is pretty much no atmosphere so the contrast will be more extreme than on earth but not quite as bad as on the moon, which was handled relatively well with film 50 years ago.

What's more interesting is pluto. Pluto's orbit is rather eccentric so the distance to the sun can be between 30 and 49 astronomical units. (Those being 150 million km, the distance from the earth to the sun.)

So that means that on pluto the light is between 1/900th and 1/2400th of the light here on earth, or about 10 or 11 stops. So rather than f/16, ISO 100, 1/125 on earth, you'd have to use something like f/11, ISO 800 and 1/2.

The New Horizons cameras have apertures between f/8.7 and f/12.6, no info about ISO. Also note that for these planet exploring spacecraft it's common to have monochromatic sensors that are exposed with different color filters one at a time to get color images.

BTW, what I've always wondered about is how those space cameras do their focusing.

A while ago we had a disagreement about whether sunny 16 always applies regardless of how far above the horizon the sun is. My take, partially from living at 52 degrees north, is that this does make a difference.
Click to expand...
New Horizons actually slewed the spacecraft to minimize motion blur during the photographic exposures of Pluto in relatively dim light. The data from instruments and photos were stored onboard and due to the vast distance and low data rate, it took about a year to transfer all of the data from the flyby back to earth.

Another fun fact is that New Horizons was the fastest ever launched spacecraft; after launching on its trajectory for a ten year trip to Pluto, it was going (relative to Earth), 58500kph or 36400mph.
 
Heritage Cameras said:
bobn2 said:
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
Click to expand...
Actually, the "average scene reflectivity on Mars" is often "the same as that on Mars"... but possibly not the same as that on Earth...;-)
Click to expand...
Thanks for the correction, it was needed.
Heritage Cameras said:
Of course, if a close up shot is too dark you can ask a Martian to hold your flash for you.
Click to expand...
You can have a really advanced lighting setup with seven strobes.
 
Dareshooter said:
I don’t know about Mars but when I take photos of the Moon from Earth I use fill flash with the onboard unit to help lighten the shadows on it’s craters. I learned this in my home on the planet Zarg.
Click to expand...
But surely if you take photos of the Earth from Mars the Sunny 16 rule still applies :? Or maybe because it's on Mars it has to be the Sunny 8.
 
bobn2 said:
Joseph S Wisniewski said:
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL
Click to expand...
Mars is 134 million miles from the Sun. The earth is 93 million.

Your gut should tell you that ratio is close to sqrt(2j so the inverse square law would put it right around one full stop, not two.
Click to expand...
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
Click to expand...
Not really since the Sunny-16 Rule is based on incidence light.

But i would shoot (slight over-exposure) @ f/8. I might even try ETTR to f/5.6 because it appears to be rather "flat"-teflectivity, ("red" w/out "white"-highlights to worry about).
 
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iljitsch said:
BTW, what I've always wondered about is how those space cameras do their focusing.
Click to expand...
Pretty much everything is at apparent local infinity.
 
PhotoTeach2 said:
bobn2 said:
Joseph S Wisniewski said:
JohnSil said:
Yes the crude math in my head tells me that if I shoot sunny 16 on Earth then it must be about sunny 8 on Mars! LoL
Click to expand...
Mars is 134 million miles from the Sun. The earth is 93 million.

Your gut should tell you that ratio is close to sqrt(2j so the inverse square law would put it right around one full stop, not two.
Click to expand...
It would depend also on the average scene reflectivity on Mars being the same as that on Mars, which is possibly not the case.
Click to expand...
Not really since the Sunny-16 Rule is based on incidence light.
Click to expand...
Think hard about what you just said.
 
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