# Why are exposure times so long if light travels so fast?



## snapsnap1973 (Jan 3, 2015)

How come the camera needs say even 1 second to capture light if light travels at 186,000 miles a second?  Also, I'm having trouble understanding WHY if the shutter is open longer (say 4 seconds) why there would be motion blur.

For example, say for the first second the scene is recorded by the sensor and then the 2nd second a bird flys by.  How do those 2 events get recorded into one image and WHAT determines WHAT gets recorded at what time?

For example, say there was a red house behind the bird, but before the bird flew by in the 2nd second (of 4 seconds) the entire red house was recorded somewhere (where?) and then the bird flys in front of the red house.  What time frame in those 4 seconds determines if the bird blocks out part of the red house as a blur maybe?

I mean say for the first second there's NO BIRD and then it flys by in the 2nd second and then he's gone in the 3rd second and 4th second of exposure.  Does the bird appear in the final picture as a blur?

This is kind of confusing.

I'm especially though having trouble with the fact that the shutter being open a little longer would allow more light in.  If light travels so quickly why wouldn't it all end up at the sensor in a fraction of a second and just be recorded?

How would allowing more light in over a period of time alter the picture?

Say, I draw my blinds in the morning.  The light just shoots in and lights up the room instantaneously and everything is visible just as it is.  It doesn't become MORE visible in a matter of seconds unless of course the sun gets higher or a cloud moves out of the way, etc.

This is got me a little irritated thinking about it.


----------



## KmH (Jan 3, 2015)

Because of the inverse square law.
The longer a shutter is open, the more chance moving objects will be blurred in a photo because the camera is not also moving.

Motion blur can be mitigated by using a technique known as panning. Panning allows the main subject to be in focus but the background is blurred.


----------



## Vtec44 (Jan 3, 2015)

Read up on exposure triangle (ISO, shutter speed, aperture) and try to understand the function of each in relation to exposure, flash, and motion.

The speed of light has nothing to do with how much of that light can be captured by the camera sensor.   If I'm in a dark room completely closed with no windows, speed of light has no effect on the brightness of that room until I have a window, and open it, to let more light into the room.


----------



## 480sparky (Jan 3, 2015)

It don't matter HOW fast light travels.  It's a matter of how MUCH light the camera receives.

Motion blur occurs because the subject MOVES across the field of view in relation to the camera.


----------



## bratkinson (Jan 3, 2015)

480sparky said:


> It don't matter HOW fast light travels.  It's a matter of how MUCH light the camera receives.


^^^^^^^^
That!

I think of exposure like filling a swimming pool...The diameter of a soda straw, garden hose, fire hose are like the aperture of a lens.  How long the water runs is shutter speed.  The water pressure used...dribble to city water main pressure(GPM) is how slow or fast the sensor reacts to the light (sort of).  Needless to say, using a soda straw at 500 PSI will shoot a stream a good distance (if it doesn't burst), but it will still take nearly forever to fill the pool. Whereas a fire hose at 500PSI will fill it in an hour or so.


----------



## JustJazzie (Jan 3, 2015)

Think of your sensor as a "cup" the longer the faucet stays open, the more "water" (light) reaches the vessel. close the faucet and no more water (light) enters.

You need a certian amount of light (correct exposure) to "fill" your sensor . Too much light and it "over flows" (turns white) Too little light and it's not "full" (underexposed or black frame results)

Your aperture is how "open" your "faucet" is. Your shutter speed is the amount of time you allow light to "fill" the "cup" (sensor). Your Iso is how large of a "cup" you need to fill.

Probably a terrible analogy, but it works.


----------



## Designer (Jan 3, 2015)

The camera sensor starts adding up all the light "chunks" (photons) that fall upon it for as long as the shutter is open.  If the shutter is open for a longer time, more of those photons are accumulated, giving you a brighter exposure.

Not all sensors can grab photons at the same rate.  Some sensors are more sensitive than others, and you can shift the sensitivity of your sensor by increasing the ISO number.


----------



## qleak (Jan 3, 2015)

Woo hoo that's quite a few questions:



snapsnap1973 said:


> How come the camera needs say even 1 second to capture light if light travels at 186,000 miles a second?


Photographs are on a recording medium. It's usually either a sensor or film. The photons (light) carry energy. It takes a certain amount of energy to produce a picture.



snapsnap1973 said:


> Also, I'm having trouble understanding WHY if the shutter is open longer (say 4 seconds) why there would be motion blur?



When a subject is moving, the light can be transmitted to different parts of the sensor or film. If enough energy from the same place hits on different parts of the sensor the result will be blur or multiple images depending on if the light is constant or not.



snapsnap1973 said:


> For example, say for the first second the scene is recorded by the sensor and then the 2nd second a bird flys by.  How do those 2 events get recorded into one image and WHAT determines WHAT gets recorded at what time?





snapsnap1973 said:


> For example, say there was a red house behind the bird, but before the bird flew by in the 2nd second (of 4 seconds) the entire red house was recorded somewhere (where?) and then the bird flys in front of the red house.  What time frame in those 4 seconds determines if the bird blocks out part of the red house as a blur maybe?


If the bird is flying and the amount of energy transmitted by the light off the bird is low enough it will not appear at all. If a strobe light fires as the bird flys across you may get multiple sharp birds. If you shine a flashlight on the bird as it flies across it will be blur.



snapsnap1973 said:


> I mean say for the first second there's NO BIRD and then it flys by in the 2nd second and then he's gone in the 3rd second and 4th second of exposure.  Does the bird appear in the final picture as a blur?



It depends.




snapsnap1973 said:


> I'm especially though having trouble with the fact that the shutter being open a little longer would allow more light in.  If light travels so quickly why wouldn't it all end up at the sensor in a fraction of a second and just be recorded?



Speed doesn't mean there is more of it. Think about a motorway, 10 cars can travel down the road at 50mph or 1 car at 50mph. The 10 cars will have more energy than the 1 car. So the important thing for exposure is the amount of light reaching the camera, not the speed of it.



snapsnap1973 said:


> How would allowing more light in over a period of time alter the picture?


It's like taking several smaller pictures and adding them together. Here's how this has been done:
Faking an ND Filter for Long Exposure Photography - DIY Photography


----------



## photoguy99 (Jan 3, 2015)

Light flows in on to whatever. It is then for the most part absorbed. Some reflects , usually to be absorbed by something else.

The more intense the light, the more is absorbed, so light never 'piles up'.

Your sensor absorbs light just like anything else. If there's not much light falling on it, it's not absorbing much. If there's more it is.

Imagine you're drawing a picture by pouring ink, very carefully, on a sheet of blotter paper. If you have a microscopic pitcher of ink, it'll take a while. If you have a great big bucket, your image will appear pretty fast.

The important difference between light and ink here is that the light will eventually... evaporate? Vanish? It goes away after a while, unlike ink.


----------



## Trever1t (Jan 3, 2015)

Yes, if you have a 4 second exposure (and it's proper for the conditions) and bird was in the frame for one second...it WOULD BE a blurr...if we even saw it.


----------



## sashbar (Jan 3, 2015)

Light is a flow of tiny "packets" called photons and exhibits properties of both waves and particles hence it's wave-particle duality. A sensor needs to collect a certain amount of photons for the analogue signal to reach a certain strength. In low light where the number of emitted and absorbed photons is small, it takes time. It does not matter how fast are photons, what matters is the cumulative energy collected by a sensor i.e. the number of photons.


----------



## Designer (Jan 3, 2015)

In case anyone is interested in how light theory is changing, I found this:

new theory of light


----------



## snapsnap1973 (Jan 3, 2015)

Ok thanks all that helped a little bit, BUT I'm still having some trouble understaning something.

Say, we've got a scene (hipothetically) with NOTHING moving in it and no more or less light entering it, it's stagnant.  How would it make a difference in the final picture if I left the shutter open for 1/1000 of a second or 30 seconds??

I mean why the heck would a sensor need a whole 30 seconds to capture an image??  I really don't get it.  I mean if I wanna take a picture of a blue mailbox, why would I want to leave the shutter open for 30 seconds instead of just snapping the same exact image in 1/1000 of a second?

Also, during a whole 30 seconds, what's going on with the camera's sensor?  What info is being saved and where?  Is that entire 30 seconds getting written to a file on the SD Card and isn't the stuff that happened in the first 10 seconds being overwritten anyway?

For example, what if I press the shutter and it's set to 30 seonds and a lightning bolt strikes in the first second.  What happens to that lightning bolt image?  If it's not recorded in the final image then what's the point of having the shutter open for a whole 30 seconds?

This is confusing.  I can't find any info on the web to read up on it either.  All the article just repeat the whole birds eye view of the process, so that it all remains a mystery, but I really want to understand it.

I understand ISO and APERTURE that I can grasp, but I just don't get the shutter speed thing and how with todays fast sensors 30 seconds would do something that couldn't be done in a fraction of a second.

UPDATE**  Darned after posting this I found this article.  Looks like someone was just as confused as I was:
Digital camera sensors and long exposures - Electrical Engineering Stack Exchange

sorry


----------



## TCampbell (Jan 3, 2015)

Image sensors have something called "wells" which collect light.  You can think of each of these as if it's a tiny little bucket.  The bucket collects "photons" of light... but you can think of these like drops of water.

If I have a bucket which can hold precisely 100 drops of water (at which point it would be "full"), then a bucket which hasn't collected any drops while the shutter is open will render as "black" and a bucket which received the full 100 drops would render as "white".  A bucket which receives somewhere between 1 to 99 drops would be rendered as some shade of gray.

But note my bucket has a limit... if I try to collect 101 drops in a bucket, I can't do it... at 100 drops my bucket is "full" and the 101st drop will spill over.  This means it is not possible for my "bucket" to sense whether there were 101 drops... vs. 200 drops...vs. 2000 drops because 100 is the limit.  That's all it can register.  This limit is referred to as the "well depth".

Suppose I have a camera that has a well-depth that allows it to collect 1000 drops of water... instead of 100.  That sensor has greater "dynamic range".  It can detect more gradients between black and white.  It is more difficult to over-flow the wells on that sensor.

The drops of water (photons) are all received at the speed of light.  But some areas are more saturated with photons than other areas.  Think of dark areas as having very few photons (like it's barely even sprinkling).  Think of bright areas as having many photons (it's a torrential downpour of "rain drops".)

When you meter an exposure, you are trying to determine what settings to use so that the sensor will become "about half full" of light in those "buckets".  This way... you have lots of wiggle room for dark areas (where you get hardly any drops of water) and bright areas (where you get lots of drops of water) and you can do this without clipping or over-flowing the limits of the "bucket".

"Wells" and "well depth" are usually not listed as specs on a typical camera.  Cameras used for astro-imaging usually will list this information.  But all digital cameras have the concept whether the manufacturer lists it or not.


----------



## sashbar (Jan 3, 2015)

snapsnap1973 said:


> Ok thanks all that helped a little bit, BUT I'm still having some trouble understaning something.
> 
> Say, we've got a scene (hipothetically) with NOTHING moving in it and no more or less light entering it, it's stagnant.  How would it make a difference in the final picture if I left the shutter open for 1/1000 of a second or 30 seconds??
> 
> ...



The sensor is collecting photons emitting from the blue box for the whole 30 second.  You are completely wrong thinking that it takes the initial moment to capture an image. Imagine a water running from a tap.  You need to hold a cup for a certain time to fill it with water. You do not fill the cup in the first 1/1000 of a second. The stronger the flow, the less time you need. It is exactly the same with light - we just have photons instead of water molecules. The brighter is the scene the stronger is the flow of photons and the less time you need to "fill the sensor".  If you shoot in the dark, just imagine the tab that is just dripping. That is how long you will hold the cup, and that is how slow will be your shutter speed.
Now, imagine a tap that is moving around while you hold the cup. The water is being splashed all over the sink, your shirt, your trousers etc. Do you feel your trousers are wet? That is where the blur comes from.


----------



## 480sparky (Jan 3, 2015)

snapsnap1973 said:


> .........
> Say, we've got a scene (hipothetically) with NOTHING moving in it and no more or less light entering it, it's stagnant.  How would it make a difference in the final picture if I left the shutter open for 1/1000 of a second or 30 seconds??.......




Take a 5-gallon bucket and put a hose in it.  Turn the water on.  How long did it take to fill the bucket?

Now, take the same 5-gallon bucket and stand at the bottom of Niagara Falls.  Fills up a lot faster, didn't it?


Niagara Falls has a LOT MORE water traversing the same space as your dinky little hose did.  It may be moving at the same speed, it's just there MORE OF IT.


In a dark scene, there's not many photons (drop of water) striking the sensor (your 5-gallon bucket), so it takes* more time* to fill up those photo-wells.  That's the same as your hose.  In a bright scene, there a _lot more_ photons headed toward the camera, so the photo-wells get filled up *faster*.  That's Niagara Falls.


----------



## qleak (Jan 3, 2015)

snapsnap1973 said:


> Say, we've got a scene (hipothetically) with NOTHING moving in it and no more or less light entering it, it's stagnant.  How would it make a difference in the final picture if I left the shutter open for 1/1000 of a second or 30 seconds??



No light. No picture it doesn't matter the exposure time. Photographers have used this to their benefit for years. Filming lightning or fireworks on a dark night you can open the shutter, wait for the flash, then close the shutter.



snapsnap1973 said:


> I mean why the heck would a sensor need a whole 30 seconds to capture an image??


You need to learn a bit about the exposure triangle. This is all about tradeoffs and choices on the part of the photographer and artistic vision. Things look different under different shutter speeds.



snapsnap1973 said:


> I really don't get it.  I mean if I wanna take a picture of a blue mailbox, why would I want to leave the shutter open for 30 seconds instead of just snapping the same exact image in 1/1000 of a second?



Again artistic vision an choices on the part of the photographer. It will not be the same image. Maybe there is so much noise when the ISO is raised image quality suffers. Maybe the photographer wants to stop down the lens more to get a greater depth of field. These choices become even more interesting when you think about moving subjects especially moving water.



snapsnap1973 said:


> Also, during a whole 30 seconds, what's going on with the camera's sensor?  What info is being saved and where?  Is that entire 30 seconds getting written to a file on the SD Card and isn't the stuff that happened in the first 10 seconds being overwritten anyway?


No. To oversimplify: Pretend there is a turnstile on each pixel and it counts the number of photons entering. 0=black depending on the camera something like 16384=white. It's adding, not taking separate images.
Adjusting the ISO adjusts the levels for black and white.  There is rarely pure darkness on the earth unless you go spelunking.



snapsnap1973 said:


> For example, what if I press the shutter and it's set to 30 seonds and a lightning bolt strikes in the first second.  What happens to that lightning bolt image?  If it's not recorded in the final image then what's the point of having the shutter open for a whole 30 seconds?


Good example. It depends on how much extra ambient light is reaching the sensor. If it's dark, you will only get the lightning, assuming that you have sufficient sensitivity 



snapsnap1973 said:


> This is confusing.  I can't find any info on the web to read up on it either.  All the article just repeat the whole birds eye view of the process, so that it all remains a mystery, but I really want to understand it.


Maybe a video.


----------



## snapsnap1973 (Jan 3, 2015)

sashbar said:


> You do not fill the cup in the first 1/1000 of a second.


 
Ok, but then how do people take great pictures at 1/1000 or greater speeds?  Is it simply that the light is more abundant so they don't need as long?

If a sensor takes 30 seconds though to capture all the light it needs from an image in my opinion it must be pretty darned slow.  I just can't understand anything digital or electronic needing longer than a fraction of a second to gathering all the "info" it would need for making an image from light, but I guess I'm off base somewhere here.

How come when we look at a scene we humans capture all the light within a split second to percieve the scene, but a modern digital camera may require 30 seconds to gather that info?  I don't get this.

P.S.  When would I need to use an shutter speed longer than a second in real life?


----------



## qleak (Jan 3, 2015)

snapsnap1973 said:


> Ok, but then how do people take great pictures at 1/1000 or greater speeds?  Is it simply that the light is more abundant so they don't need as long?



Artistic vision. Sometimes things look cooler under slow shutter speeds. Some crazy people, myself included, strap filters to reduce light on our cameras to take slow shutter speed shots ( from a tripod ) when the light is bright.




snapsnap1973 said:


> If a sensor takes 30 seconds though to capture all the light it needs from an image in my opinion it must be pretty darned slow.  I just can't understand anything digital or electronic needing longer than a fraction of a second to gathering all the "info" it would need for making an image from light, but I guess I'm off base somewhere here.



Star trails? Here's a 267 second exposure.











snapsnap1973 said:


> How come when we look at a scene we humans capture all the light within a split second to percieve the scene, but a modern digital camera may require 30 seconds to gather that info?  I don't get this.
> 
> P.S.  When would I need to use an shutter speed longer than a second in real life?



Human perception is not how your camera captures. Human vision has higher dynamic range and is interpreted by your brain.


----------



## Designer (Jan 3, 2015)

It's not necessarily a slow sensor, maybe there just isn't a lot of light (say at night, for instance).  

Sensors are not eyes.


----------



## 480sparky (Jan 3, 2015)

snapsnap1973 said:


> Ok, but then how do people take great pictures at 1/1000 or greater speeds?  Is it simply that the light is more abundant so they don't need as long?
> 
> If a sensor takes 30 seconds though to capture all the light it needs from an image in my opinion it must be pretty darned slow.  I just can't understand anything digital or electronic needing longer than a fraction of a second to gathering all the "info" it would need for making an image from light, but I guess I'm off base somewhere here.
> 
> ...




Why does it take your entire lifetime to earn all that money?

Why can't I just get paid $5,000,000 on my first paycheck and be done with it?


----------



## Vtec44 (Jan 3, 2015)

snapsnap1973 said:


> How come when we look at a scene we humans capture all the light within a split second to percieve the scene, but a modern digital camera may require 30 seconds to gather that info?  I don't get this.



I have never been able to look up into the night sky and see the Milky Way galaxy in a split second.  It doesn't work even after staring at the sky for 30 seconds.


----------



## Designer (Jan 3, 2015)

I have.


----------



## sashbar (Jan 3, 2015)

snapsnap1973 said:


> sashbar said:
> 
> 
> > You do not fill the cup in the first 1/1000 of a second.
> ...



Imagine a tap that came off and the water is pouring out of the pipe at a very high pressure. How long does it takes to fill the cup ?

Look, it is all very easy, just use your common sense.


----------



## Vtec44 (Jan 3, 2015)

Designer said:


> I have.



Your eyes must have been designed by Sony with a super sensitive sensor


----------



## photoguy99 (Jan 3, 2015)

Designer said:


> In case anyone is interested in how light theory is changing, I found this:
> 
> new theory of light




That web page has basically every single earmark of Kook on it.


----------



## DrDave (Jan 3, 2015)

Some very informative and funny info here.


----------



## qleak (Jan 3, 2015)

Vtec44 said:


> Designer said:
> 
> 
> > I have.
> ...



Light pollution is probably pretty bad in So Cal right? In some less populated areas you can see quite a bit with the naked eye.


----------



## Designer (Jan 3, 2015)

Vtec44 said:


> Designer said:
> 
> 
> > I have.
> ...


It depends on how dark the sky is.


----------



## Vtec44 (Jan 3, 2015)

So Cal is not always 75 degrees, warm beach, and fake boobs.   We have huge national forests that are completely untouched.  My home studio is a short 15 mins drive to  San Bernardino National forest.  I go deer hunting there every year, 2am in the morning pitch black sitting on my tree standk, looking up to the beautiful sky with no major towns within 30 miles.  I've never been able to see the Milky Way the way that my camera does.  Maybe my eye sight is not as good as some of you...


----------



## TCampbell (Jan 3, 2015)

Vtec44 said:


> So Cal is not always 75 degrees, warm beach, and fake boobs.   We have huge national forests that are completely untouched.  My home studio is a short 15 mins drive to  San Bernardino National forest.  I go deer hunting there every year, 2am in the morning pitch black sitting on my tree standk, looking up to the beautiful sky with no major towns within 30 miles.  I've never been able to see the Milky Way the way that my camera does.



The San Bernadino Natl Forest has Bortle 5-6 skies (if you use the color zones then it's mostly an "orange" zone and "yellow" zone.

I've been sailing up the North Channel of Lake Huron... these are Bortle 7-8 skies ("black" zone).  It makes a HUGE difference!  

On a moonless night with Bortle 7-8 skies... the Milky Way jumps off the sky at you and looks like a photograph.  Your eyes absolutely see what you see in those long exposure photos.  Your eyes must be dark-adapted (if you've switched on a lightbulb in the last 30 minutes... you're going to have to wait a while before your eyes adjust.)  Eyes can mostly dark-adapt in about 20 minutes... but it takes closer to 40 minutes to be fully dark-adapted.  Switching on a light for just a moment destroys the dark-adaption and you have to wait again.


----------



## runnah (Jan 3, 2015)

Like they say at an Appalachian key party, it's all relative.


----------



## Vtec44 (Jan 3, 2015)

I guess I'll have to take your words for it... since I haven't been able to see it in person


----------



## 480sparky (Jan 3, 2015)

TCampbell said:


> The San Bernadino Natl Forest has Bortle 5-6 skies (if you use the color zones then it's mostly an "orange" zone and "yellow" zone.
> 
> I've been sailing up the North Channel of Lake Huron... these are Bortle 7-8 skies ("black" zone).  It makes a HUGE difference!
> 
> On a moonless night with Bortle 7-8 skies... the Milky Way jumps off the sky at you and looks like a photograph.  Your eyes absolutely see what you see in those long exposure photos.  Your eyes must be dark-adapted (if you've switched on a lightbulb in the last 30 minutes... you're going to have to wait a while before your eyes adjust.)  Eyes can mostly dark-adapt in about 20 minutes... but it takes closer to 40 minutes to be fully dark-adapted.  Switching on a light for just a moment destroys the dark-adaption and you have to wait again.



Methinks you have your scale backwards.


----------



## qleak (Jan 3, 2015)

480sparky said:


> Methinks you have your scale backwards.



He's referring to naked eye limiting magnitude (the NELM column):

Bortle scale - Wikipedia, the free encyclopedia


----------



## 480sparky (Jan 3, 2015)

qleak said:


> 480sparky said:
> 
> 
> > Methinks you have your scale backwards.
> ...



Which is 'reversed' compared to the (referred-to) Bortle scale.


----------



## Designer (Jan 3, 2015)

Not to be-labor the freakin' point, but we lived about 15 miles from any sizable town, and aside from our own freakin' yard light, there was no freakin' light.  just look up and see the freakin' Milky Way.


----------



## photoguy99 (Jan 3, 2015)

Nerd.


----------



## Trever1t (Jan 3, 2015)

best thread this month. gotta be some good hooch, that's all I'm sayin'


----------



## Designer (Jan 3, 2015)

three glasses of wine with supper


----------



## Designer (Jan 3, 2015)

I'd better not post the one I had written.


----------



## DrDave (Jan 3, 2015)

...Time for a beer.


----------



## Designer (Jan 3, 2015)

DrDave said:


> ...Time for a beer.


Right.  

I had a beer before supper.


----------



## Light Guru (Jan 3, 2015)

snapsnap1973 said:


> Say, we've got a scene (hipothetically) with NOTHING moving in it and no more or less light entering it, it's stagnant.  How would it make a difference in the final picture if I left the shutter open for 1/1000 of a second or 30 seconds??
> 
> I mean why the heck would a sensor need a whole 30 seconds to capture an image??  I really don't get it.



Again it had NOTHING to do with how fast light moves, it has EVERYTHING to do with how much light there is.


----------



## Bebulamar (Jan 3, 2015)

SnapSnap you must be a genius! I have never heard anyone posing your question so you have my vote for being creative. But sorry I think your question is a challenge to us and not one of a wondering mind so there is no answer for you.


----------



## tecboy (Jan 3, 2015)

Who cares? Just go outside and take good pictures.  That's all that matter.


----------



## Vtec44 (Jan 3, 2015)

tecboy said:


> Who cares? Just go outside and take good pictures.  That's all that matter.



...and make sure to get paid for it.  Else, it's going to be expensive.


----------



## Trever1t (Jan 3, 2015)

stick a fork in it, turn it over, it's done!


----------



## snapsnap1973 (Jan 4, 2015)

Ok, so if the sensor is collecting photons from the blue mailbox for 30 seconds what will be the end result in final image form from say a 1000 of a second exposure.  Just a brighter picture?

Would someone need to use a 30 seconds exposure normally in broad daylight, for example?  What would be the end result if I was at say 100 ISO and took a picture at 30 seconds shutter speed on a beautiful sunny day outside?  My guess that the picture would be very "white" .  Am I off base?

So are underexposed pixels black and over exposed white in a final image?  Everything in between is a color other than black or white?

How am I doing?   Am I a pro photographer yet?   LOL


----------



## 480sparky (Jan 4, 2015)

snapsnap1973 said:


> .........Would someone need to use a 30 seconds exposure normally in broad daylight, for example?  .......



Yes.  Commonly done to get that silky-smooth effect when shooting moving water such as waterfalls.


----------



## Vtec44 (Jan 4, 2015)

I've done long exposure in bright day light before... with a 10 stops ND filter


----------



## snapsnap1973 (Jan 4, 2015)

I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.

For example, a person running across the image and then the final image has him or her in 4 different places at once (as various blurs of course).  I don't get how that can happen really.  It's boggling my mind!


----------



## 480sparky (Jan 4, 2015)

snapsnap1973 said:


> I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.......!



Put some wet paint on your finger, press said finger against a canvas, then move your finger around.

The paint smears, doesn't it?  Because your finger moved over time.

A subject reflecting light toward a camera is the same thing.  The subject is your finger, the light is your paint and the camera is your canvas.


----------



## snapsnap1973 (Jan 4, 2015)

480sparky said:


> snapsnap1973 said:
> 
> 
> > I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.......!
> ...



Thanks, I think I might be getting it now!  

That helped!


----------



## wfooshee (Jan 5, 2015)

snapsnap1973 said:


> I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.
> 
> For example, a person running across the image and then the final image has him or her in 4 different places at once (as various blurs of course).  I don't get how that can happen really.  It's boggling my mind!



Define "instant." Your own example of a 30-second exposure is not exactly instantaneous, is it? The camera does not choose one particular instant of time during that 30 seconds and record that instant. It captures everything it sees during that time, so there is no "instant."

The sensor captures everything it sees in that time, but obviously not as motion.

Exercise to illustrate motion blur: extend your arm out to its full length in front of you, on a bright day, with your hand in front of a dark surface. A wall, the fridge, your car, the Black Forest, whatever. Enough contrast that your hand is brighter than what's behind it.

Raise your index finger like you're counting to ONE.

Now shake your hand back and forth sideways as rapidly as you can.

While it's moving, does your eye see your finger sharply defined, or do you see "through" a wide stretched-out distorted view of your finger.

If a camera takes a picture of that movement with a shutter speed of 1/8000 of a second, the camera will capture a sharp image of your hand and finger. If instead you run the shutter at 1/2 of a second, the camera will not be able to resolve the finger, but will have that streak of finger-color in the space your finger moved through. The camera looked at the scene long enough to see the motion, which it recorded as the blur you saw in the exercise above.


----------



## pgriz (Jan 5, 2015)

Here's a little exercise that can help you.  Set your mode to shutter priority.  Set your shutter speed to (say) 1/10 sec.  Now, take a picture of people walking in a plaza.  You'll might get the image of a person walking past you.  If the timing is right, you'll see the person's foot "frozen" on the ground, and an increasing blur as you look up the person.  That's because the foot hasn't moved in the 1/10 sec, whereas the rest of the body is moving.  The leg will be almost completely sharp at the ankle, and probably quite blurred by the hip.  This illustrates one of the various ways that using the shutter speed can improve your artistic vision.


----------



## wfooshee (Jan 5, 2015)

^^^^^ Hahaha! Something I actually did a couple of weeks ago at a local city park! 2 seconds exposure.


----------



## Forkie (Jan 6, 2015)

snapsnap1973 said:


> I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.
> 
> For example, a person running across the image and then the final image has him or her in 4 different places at once (as various blurs of course).  I don't get how that can happen really.  It's boggling my mind!




The camera only catches an "instant" if you set your shutter speed to an "instant".

Let's assume that an "instant" is 1/1000th of a second:

If you shoot a bird flying at 50 miles per hour at a shutter speed of 1/1000th of a second.  In the time it takes your shutter to open and close again the bird has only travelled 0.02 metres (or 2 centimetres):

50mph = 22.35 metres per second

22.35200 divided by 1000 = 0.022 (2 centimetres)  - you catch that 2 centimetres of movement with a shutter speed of 1/1000th of second.

2 centimetres is more or less imperceptible if the bird is any distance away due to the parallax effect (a WHOLE different topic!) so you get a solid, sharp image of a bird in flight.

*NOW:*

Try the same shot with a 5 second shutter speed:

50mph = 22.35200 metres per second x 5 seconds = 111.76 metres.

So, in the time it has taken your shutter to open and close again, the bird has travelled over a hundred metres.  Because your shutter was open for that whole 111 metres, it captures all the motion from the start of that 5 seconds to the end, and because you've captured a whole 5 seconds and not an "_instant_", you can see that full 111 movement across the sensor.


----------



## Braineack (Jan 6, 2015)

snapsnap1973 said:


> For example, a person running across the image and then the final image has him or her in 4 different places at once (as various blurs of course).  I don't get how that can happen really.  It's boggling my mind!



This is about as confusing as dipping your paint brush in paint, then dragging it across your canvas and wondering how a line was captured.


----------



## EIngerson (Jan 6, 2015)

bump


----------



## runnah (Jan 6, 2015)

EIngerson said:


> bump



@$$hole!


----------



## Light Guru (Jan 6, 2015)

snapsnap1973 said:


> I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.
> 
> For example, a person running across the image and then the final image has him or her in 4 different places at once (as various blurs of course).  I don't get how that can happen really.  It's boggling my mind!



The camera DOES NOT capture the final image in an instant.  It is gathering light the ENTIRE time the shutter is open.  If the shutter speed is 1/100sec  it is capturing light for 1/100sec if the shutter is open for 30 seconds it is capturing light for the entire 30 seconds.

As for your example the person is NOT in 4 different places at once the person was in ALL of the places from the start to the end of the blur.  You would only see the person in 4 places if they stopped and stood still in 4 different places through out the course of the exposure. 

Again the camera DOES NOT capture the final image in an instant.  It is gathering light the ENTIRE time the shutter is open. This is why its the amount of light NOT the speed of light that matters when exposing your image.


----------



## pixmedic (Jan 6, 2015)

Light Guru said:


> snapsnap1973 said:
> 
> 
> > I'm still having trouble with understanding the "blur" thing, but I guess I'm gonna have to do some research.  I don't get how "movement" can be captured into a final image if a camera captures something at an instant in time.  Obviously a "blur" shows movement.
> ...


What would happen if you were traveling at the speed of light when you took the picture?


----------



## Light Guru (Jan 6, 2015)

pixmedic said:


> What would happen if you were traveling at the speed of light when you took the picture?



Depends on the shutter speed. If we could have a shutter speed fast enough your movement would be captured just like how we capture a runner in a photo now.


----------



## photoguy99 (Jan 6, 2015)

pixmedic said:


> Light Guru said:
> 
> 
> > snapsnap1973 said:
> ...



For starters your camera would be extremely heavy


----------



## pgriz (Jan 6, 2015)

pixmedic said:


> What would happen if you were traveling at the speed of light when you took the picture?



Well, assuming we could do the impossible (which is to accelerate matter to the speed of light), you'll find that "time" now stops,and any time-related attribute becomes meaningless.  This comes from the observation that time as perceived by the traveller who is accelerating to faster and faster speeds becomes slower and slower.  
See: Time Dilation - How time isn't the contant it seems to be for discussion of this phenomenon.


----------



## photoguy99 (Jan 6, 2015)

On the up side, shutter speed hardly matters as things outside your reference frame will be frozen still.

You better have great panning technique, though.


----------



## petrochemist (Jan 6, 2015)

pixmedic said:


> What would happen if you were traveling at the speed of light when you took the picture?


 
Speeds are all relative. From the point of view of a photon travelling towards you, you are travelling at the speed of light! 

Getting something with mass to approach something else with mass at the speed of light will require infinite energy. Getting close to the speed of light is theoretically possible but time gets complicated above ~0.98c.


----------



## 480sparky (Jan 6, 2015)

pixmedic said:


> What would happen if you were traveling at the speed of light when you took the picture?



Do you need to turn on your headlights for that?


----------



## DrDave (Jan 6, 2015)

At the speed of light, electromagnetic resonance would approach critical mass inversely proportional  to the photons resonating frequency which would then allow you to photograph infinity!


----------



## robbins.photo (Jan 6, 2015)

pixmedic said:


> What would happen if you were traveling at the speed of light when you took the picture?



It would depend entirely on whether your windows were rolled up, or down of course.

Physics!

Lol


----------



## Braineack (Jan 6, 2015)

sometimes i think scientists make up rules/law that explain things like the inability to travel at the speed of light, with long math formuals that no one really can understand just as a way to prove things we dont understand.


----------



## Fire (Jan 6, 2015)

Im amazed at how many responses there is! You guys rock!


----------



## snowbear (Jan 6, 2015)

Fire said:


> Im amazed at how many responses there is! You guys rock!


Boredom


----------



## TCampbell (Jan 7, 2015)

pgriz said:


> pixmedic said:
> 
> 
> > What would happen if you were traveling at the speed of light when you took the picture?
> ...




^^ This

It isn't just that it's just not possible to travel _faster_ than the speed of light.  We can't actually travel _at_ the speed of light.

If you could truly reach the speed of light, time would stop completely.   If you pick on a star in the Andromeda galaxy (nearly 3 million light years away... which means traveling "at the speed of light" it takes 3 million years for it's light to reach us) and take the point of view of a single photon of light... time has "stopped" for that photon.  The light from those distant stars is _simultaneously_ released from the star AND absorbed by your eye... at the _same time._  From that perspective of that photon, it's speed did not change... rather the distance in space compressed to nothing.  But keep in mind that's from the point of view of the "photon" of light.  To us, that journey took nearly 3 million years and space was not compressed.

Here's a pretty good video which explains both special and general relatively with some great examples.






And while it all seems impossible and crazy, there are not only experiments and observations to confirm it's accuracy, we take many every-day technologies for granted which RELY on this theory in order to work at all (if they didn't account for it, they wouldn't function...  GPS devices are a great example.)


----------



## 480sparky (Jan 7, 2015)

TCampbell said:


> .... The light from those distant stars is _simultaneously_ released from the star AND absorbed by your eye... at the _same time._  ..........



Which would suck.  Big time.

Because you'd end up seeing _everything_ in the entire universe........ _all at once_.  You'd end up blind.


----------



## robbins.photo (Jan 7, 2015)

480sparky said:


> TCampbell said:
> 
> 
> > .... The light from those distant stars is _simultaneously_ released from the star AND absorbed by your eye... at the _same time._  ..........
> ...



Which is why I prefer the Capt Kirk version of physics.  "Ok we're here.  Trot out the green alien babes!"

Lol


----------



## greybeard (Jan 7, 2015)

The way it works is an actual upside down image of your picture is projected onto the sensor of the camera.  Think of it like the image is being burned into the sensor.  The brighter the image, the shorter the amount of time needed to burn it in and the dimmer the image then the longer.


----------



## runnah (Jan 7, 2015)




----------



## runnah (Jan 7, 2015)




----------



## runnah (Jan 7, 2015)




----------



## runnah (Jan 7, 2015)




----------



## deeky (Jan 8, 2015)

This has gotten quite amusing.  I think what everyone is trying to say is that you are WAAAAAAYYYY overthinking this.  Rather than reading online, pick up your friggin camera and go shoot something.  Put it in manual, change one setting at a time, and look at what the camera actually captures according to what you make it do.  Shoot the exact same shot only changing the shutter speed.  Then set a 2 second exposure and have someone walk through the shot.  You will quickly figure out what happens. 

By the way, the theory behind actually traveling the speed of light has made huge jumps since scientists began figuring in for hanging those fake bull balls from the back of their hypothetical vehicles.....


----------



## 480sparky (Jan 8, 2015)

If light travels so fast, why did I waste 16 minutes of my life reading this thread?


----------



## robbins.photo (Jan 8, 2015)

480sparky said:


> If light travels so fast, why did I waste 16 minutes of my life reading this thread?



Just imagine it from the perspective of the poor photon that is stuck in this thread for eternity.

Lol


----------



## Designer (Jan 8, 2015)

My photon left two days ago.


----------



## robbins.photo (Jan 8, 2015)

Designer said:


> My photon left two days ago.



Have you printed up flyers with a picture and posted them at the local gas station?  Would be a nice change of pace from the "Have you seen this cat" stuff I normally see when I stop for gas.


----------



## pgriz (Jan 8, 2015)

A couple of weeks ago, I practiced catching 2 million-year old photons, along with many of much more recent vintage.  Had to prime my rhodopsin chomophores tho.


----------



## 480sparky (Jan 8, 2015)

pgriz said:


> A couple of weeks ago, I practiced catching 2 million-year old photons,.........



How did you KNOW they were 2 million years old?  Did you card them?


----------



## pgriz (Jan 8, 2015)

Well, because they were all of the Andromedan family.  Those guys act old.   Sirian photons are mere toddlers, at 8-ish,  whereas the Pleiadians were at least 400 years old.


----------



## 480sparky (Jan 8, 2015)

You need to get out more often...........


----------



## robbins.photo (Jan 8, 2015)

pgriz said:


> Well, because they were all of the Andromedan family.  Those guys act old.   Sirian photons are mere toddlers, at 8-ish,  whereas the Pleiadians were at least 400 years old.



Waiter!  Check Please!


----------



## 480sparky (Jan 8, 2015)

Wait... what?  Andromedan, you say?  Did your blood turn to powder?


----------



## pgriz (Jan 8, 2015)

480sparky said:


> Wait... what?  Andromedan, you say?  Did your blood turn to powder?



No, but my eyes watered a bit.  However, that may have been due to the wind.  On the other hand, after your body has absorbed a 2-million year old photon, you do get nostalgic.


----------



## limr (Jan 8, 2015)

So, it would, like, not be cool to mention my 7-hour pinhole exposure and confuse the OP further, would it?


----------



## robbins.photo (Jan 8, 2015)

limr said:


> So, it would, like, not be cool to mention my 7-hour pinhole exposure and confuse the OP further, would it?



I think the OP's head exploded about a page and a half ago.. so, no harm no foul at this stage I think.  Lol


----------



## pgriz (Jan 8, 2015)

Ah why not.  But you may have to explain that you were operating your camera at f/320 or something like that.  Now the really cool experiment would be to set up a two pin-hole camera and see what light pattern emerges.  That would REALLY confuse the issue, what with the creation of interference patterns and so forth.


----------



## limr (Jan 8, 2015)

Oooh, two pinholes! 

*strokes imaginary beard in thought*


----------



## 480sparky (Jan 8, 2015)

limr said:


> Oooh, two pinholes!
> 
> *strokes imaginary beard in thought*



It ain't imaginary!


----------



## limr (Jan 8, 2015)

480sparky said:


> limr said:
> 
> 
> > Oooh, two pinholes!
> ...



Hey, it is after I shaved it off!


----------



## chuasam (Jan 11, 2015)

I can only think of one possible answer - Einstein was wrong and the Bird indeed travels faster than light.


----------



## Bebulamar (Jan 15, 2015)

Seriously since light is so fast we can assume it went from the subject to the sensor instantly. However, when it gets to the sensor it has to take time for the sensor get a good impression.


----------



## runnah (Jan 15, 2015)

Next person who brings this thread back will be punished.


----------



## bribrius (Jan 15, 2015)

well the sensor doesn't want to just jump all over the light ya know. it wants to take time, get to know the light, get acquainted before it lets the light in to be absorbed.  And it likes to go slow in increments. .


----------



## deeky (Jan 15, 2015)

bribrius said:


> well the sensor doesn't want to just jump all over the light ya know. it wants to take time, get to know the light, get acquainted before it lets the light in to be absorbed.  And it likes to go slow in increments. .



So what you are saying is that all images have a little Barry White embedded in the coding.....

Or maybe some Marvin Gaye.  Push your camera's little button and it starts singing "Let's....get it on."


----------



## bribrius (Jan 15, 2015)

deeky said:


> bribrius said:
> 
> 
> > well the sensor doesn't want to just jump all over the light ya know. it wants to take time, get to know the light, get acquainted before it lets the light in to be absorbed.  And it likes to go slow in increments. .
> ...


not all the time. just sometimes. slow. other times you put it on continuous and they like it hard and fast...


----------

