Anderson Video - Camera Focus

Professor Anderson
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<font color="#ffffff">It says, "While you are photographing a dog, it begins to move away. </font> <font color="#ffffff">What must you do to keep it in focus?"</font> <font color="#ffffff">Okay so let's go back to the camera.</font> <font color="#ffffff">The cameras just like an eyeball, right?</font> <font color="#ffffff">It's the same idea so let's draw a camera.</font> <font color="#ffffff">Here's the lens of the camera.</font> <font color="#ffffff">Here is the film plane or the CCD plane.</font> <font color="#ffffff">Okay, this is where your retina would be in your eyeball.</font> <font color="#ffffff">And it says we got a dog that we are photographing and it's in focus.</font> <font color="#ffffff">But then it's going to start to move away.</font> <font color="#ffffff">All right so we draw a dog.</font> <font color="#ffffff">Here's our dog.</font> <font color="#ffffff">Happy dog.</font> <font color="#ffffff">Okay, and we're taking a picture of this dog and he's in focus.</font> <font color="#ffffff">All right, so if I think about the rays coming off the dog when that dog is close, </font> <font color="#ffffff">how do I figure out where those rays are going to end up?</font> <font color="#ffffff">Well let's draw some focal points.</font> <font color="#ffffff">Let's say there is a focal point here.</font> <font color="#ffffff">And a focal point there.</font> <font color="#ffffff">And now this is just like our good old object.</font> <font color="#ffffff">So we're gonna erase the dog and just draw an arrow like we usually have.</font> <font color="#ffffff">Okay, and now let's see if we can figure out where it's all in focus.</font> <font color="#ffffff">Parallel rays go through the focus.</font> <font color="#ffffff">Rays through the focus go parallel.</font> <font color="#ffffff">Everything is in focus right here, at the film plane.</font> <font color="#ffffff">Good.</font> <font color="#ffffff">But now this thing is going to move further away.</font> <font color="#ffffff">Okay, and if it moves further away, we're gonna have to do something to keep it in focus.</font> <font color="#ffffff">So let's draw a picture again.</font> <font color="#ffffff">It looks like that.</font> <font color="#ffffff">But now parallel rays go through the focus.</font> <font color="#ffffff">Rays through the focus go parallel.</font> <font color="#ffffff">And look what happens.</font> <font color="#ffffff">The image should be in focus right there.</font> <font color="#ffffff">And yet our film plane is fixed.</font> <font color="#ffffff">Okay, we can't move where the film is, but we can move where the lens is.</font> <font color="#ffffff">So if I want to move that image to the film plane, which way should I move this lens?</font> <font color="#ffffff">Should I move it closer to the film or further away from the film?</font> <font color="#ffffff">I have to move it closer to the film.</font> <font color="#ffffff">If I move the lens to the right, the image is going to move to the right.</font> <font color="#ffffff">Everything is going to move to the right.</font> <font color="#ffffff">So I want to move the lens closer.</font> <font color="#ffffff">Okay, and let's see if that is the right answer.</font> <font color="#ffffff">It says, move the lens closer to the sensor, or the film sensor's CCD array</font> <font color="#ffffff">if it's like your digital SLR.</font> <font color="#ffffff">And it does say that that is the right answer.</font> <font color="#ffffff">Okay, so when things get further away, you want to move the lens closer to the film.</font> <font color="#ffffff">And, in fact, when they get out at infinity, the focal point should be at the film plane.</font> <font color="#ffffff">Okay.</font>
<font color="#ffffff">It says, "While you are photographing a dog, it begins to move away. </font> <font color="#ffffff">What must you do to keep it in focus?"</font> <font color="#ffffff">Okay so let's go back to the camera.</font> <font color="#ffffff">The cameras just like an eyeball, right?</font> <font color="#ffffff">It's the same idea so let's draw a camera.</font> <font color="#ffffff">Here's the lens of the camera.</font> <font color="#ffffff">Here is the film plane or the CCD plane.</font> <font color="#ffffff">Okay, this is where your retina would be in your eyeball.</font> <font color="#ffffff">And it says we got a dog that we are photographing and it's in focus.</font> <font color="#ffffff">But then it's going to start to move away.</font> <font color="#ffffff">All right so we draw a dog.</font> <font color="#ffffff">Here's our dog.</font> <font color="#ffffff">Happy dog.</font> <font color="#ffffff">Okay, and we're taking a picture of this dog and he's in focus.</font> <font color="#ffffff">All right, so if I think about the rays coming off the dog when that dog is close, </font> <font color="#ffffff">how do I figure out where those rays are going to end up?</font> <font color="#ffffff">Well let's draw some focal points.</font> <font color="#ffffff">Let's say there is a focal point here.</font> <font color="#ffffff">And a focal point there.</font> <font color="#ffffff">And now this is just like our good old object.</font> <font color="#ffffff">So we're gonna erase the dog and just draw an arrow like we usually have.</font> <font color="#ffffff">Okay, and now let's see if we can figure out where it's all in focus.</font> <font color="#ffffff">Parallel rays go through the focus.</font> <font color="#ffffff">Rays through the focus go parallel.</font> <font color="#ffffff">Everything is in focus right here, at the film plane.</font> <font color="#ffffff">Good.</font> <font color="#ffffff">But now this thing is going to move further away.</font> <font color="#ffffff">Okay, and if it moves further away, we're gonna have to do something to keep it in focus.</font> <font color="#ffffff">So let's draw a picture again.</font> <font color="#ffffff">It looks like that.</font> <font color="#ffffff">But now parallel rays go through the focus.</font> <font color="#ffffff">Rays through the focus go parallel.</font> <font color="#ffffff">And look what happens.</font> <font color="#ffffff">The image should be in focus right there.</font> <font color="#ffffff">And yet our film plane is fixed.</font> <font color="#ffffff">Okay, we can't move where the film is, but we can move where the lens is.</font> <font color="#ffffff">So if I want to move that image to the film plane, which way should I move this lens?</font> <font color="#ffffff">Should I move it closer to the film or further away from the film?</font> <font color="#ffffff">I have to move it closer to the film.</font> <font color="#ffffff">If I move the lens to the right, the image is going to move to the right.</font> <font color="#ffffff">Everything is going to move to the right.</font> <font color="#ffffff">So I want to move the lens closer.</font> <font color="#ffffff">Okay, and let's see if that is the right answer.</font> <font color="#ffffff">It says, move the lens closer to the sensor, or the film sensor's CCD array</font> <font color="#ffffff">if it's like your digital SLR.</font> <font color="#ffffff">And it does say that that is the right answer.</font> <font color="#ffffff">Okay, so when things get further away, you want to move the lens closer to the film.</font> <font color="#ffffff">And, in fact, when they get out at infinity, the focal point should be at the film plane.</font> <font color="#ffffff">Okay.</font>