Question on the inverse square law

[WayneF]

The close reflected paths are more added light onto the subject than the direct path inverse square law considers. In practice, its not a big problem, since it is relatively small, and TTL metering will meter the sum, and off course when we adjust compensation by eye, that takes care of it too. Any addition actually helps the other problems, like TTL BL flash being reduced by the ambient, or the D-lens focus distance being reported wrong in zooms.

It was always easy to start a wild debate about why the camera distance is not a factor of exposure, it has been debated since we had enough communication to debate it. But it is obviously not debatable that is it true, so it's really enough to just know its true.

 

[Revet]

No, exposure does not matter where the camera is (OK, technically if avoiding macro distances, other factors kick in there).

It is one of the hardest subjects to explain, so beginners sources never do. It is enough to know that the camera distance does not affect exposure.

Yes, inverse square law always exists, but our use of it is about light sources, traveling from there to us.

The camera view is a different situation, seeing an illuminated surface out there, and the area it sees is much reduced when it is close, by exactly the same inverse square law relationship, which exactly cancels out, so that camera distance is not a factor of exposure. Yes, twice closer is 4x brighter, but the camera then sees 1/2 size area (1/4 area), so the surface brightness per unit area says constant. See Camera distance does not affect exposure if you dare.

Same reason that f/4 is the same f/4, regardless of the focal length or actual corresponding aperture diameter.
So same reason that zooming in tight with a long telephoto lens does not change the brightness of the exposure.

Regarding your result, try again paying close attention to the details. Move the subject or the camera, it only matters how far the flash has to travel. But all else must be the same.




But for example, the sun gives us Sunny 16 exposures of the mountain, no matter how far the camera is from it.

Got brave this morning and read the explanation in the hyperlink. Very well stated and perfectly understandable presentation. I saw a really good figure once in a Digital Photography School E book showing what happens to the density of photon's with distance. If you imagine an image of a mountain in that figure, it is pretty easy to see that the number of photons remains the same within a far or closer up shot of the mountain. This work's great for the particle theory of light, what about the wave theory!!!!! LOL

 

[WayneF]

And what about if the flash is on the camera?

 

[Revet]

Thank you all for the comments. I think we sufficiently beat this subject to death. Time to move on!!

 

[Revet]

And what about if the flash is on the camera?

Lost me here Wayne. I thought we were discussing how a mountain has the same illumination on our sensor when we are close or far. How does a flash on or off a camera fit in here?? Please bear in mind that I haven't had my morning coffee yet so I might be missing the obvious here!!

 

[WayneF]

Lost me here Wayne. I thought we were discussing how a mountain has the same illumination on our sensor when we are close or far. How does a flash on or off a camera fit in here?? Please bear in mind that I haven't had my morning coffee yet so I might be missing the obvious here!!

Sorry, just a poor attempt at a weak joke. Camera distance is not a factor of exposure, unless the flash is on the camera.