Quote:
Originally Posted by Atmos
Basically, point light sources radiate in all directions and not just directly at anything in particular. Because they radiate in all directions, a larger aperture is able to capture more of that "all directions". If I wasn't at work I would draw a diagram on my white board, could do that when I get home :-)
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That makes sense, thanks mate.
Quote:
Originally Posted by Stefan Buda
Looks like you guys missed the recent and excellent post on this topic by Ray:
http://www.iceinspace.com.au/forum/s...d.php?t=136008
I said post rather than thread because there is no need to read past the first post.
It should have been nailed to the top but it hasn't even been pinned.. |
Nope, I got that, but that doesn't answer my original question about how aperture relates to more light instead of different light. Cheers for the link though, it was a good thread.
Quote:
Originally Posted by Shiraz
"F-ratio makes no difference to sensitivity for a given aperture IF THE PIXEL SIZE IS ADJUSTED TO COMPENSATE FOR THE CHANGE IN FOCAL LENGTH".
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Spot on Ray. He's technically correct, but his presentation is a bit misleading. I actually got that part and my main question didn't really relate to his article all that much, it's just what I was thinking about at the time. I think I should have omitted that from my post as it's largely unrelated to my main question and has served only to confuse people.
Quote:
Originally Posted by Shiraz
re the way a lens works, please forgive me if I have misunderstood your question, but here goes. If you hold up your hand and look at it, you get almost no information on where the light that you see came from - it could have been from many different sources in the room, but you can't tell anything much about those sources by looking at the light reflected from your hand. A similar scrambled pattern of light falls all over the aperture of a lens or mirror, but the lens or mirror has the ability to unscramble that light pattern and develop a map of the angles that the light came from and how bright it is - that is the image that you detect. Light from a point source falls all over the lens aperture and it is then transformed (unscrambled) by the lens back into a point in the focal plane. Light from an extended object also falls all over the aperture, but it is transformed into a 2D representation of the source object. If the aperture is bigger, more light from both point and extended sources gets into the system.
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The main thing I was confused about is why does a bigger aperture not mean light from different sources rather than more light from the same sources. To make that extreme, imagine I had a mirror the size of my thumbnail. Obviously it could only reflect light from a small area... but then if I sold my thumbnail-sized mirror and bought one the size of Queensland, it would reflect light from a much greater area simply due to its larger size, but (assuming all else is equal) the intensity of the reflected light would remain constant.
Now if the bigger aperture means that more light is focused into an area of the same size, I can see why the intensity, and resolution would increase... but how does this not also increase the "area" of light gathered, i.e. an increased FOV. Unless it does but because the recording medium was already fully illuminated (presumably), the extra FOV just bypasses it? In which case if you had a system where the sensor was not fully illuminated, keeping everything constant except the aperture would result in a sensor that is more fully illuminated with data that was previously not recorded...?