krashzmom wrote:
gessman wrote:
krashzmom wrote:
wow! That really is a great sight. I haven't had time yet to study it but I will.. Thanks a bunch Gellman.
I don't know about the first site but I know even my curiosity won't make me open the 2nd one and I guess I qualify as a kind of wannabe so if you experts will tell me if they are real or not, I still don't know if I'll believe you.
quote=anotherview This interesting Web site helps... (
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It's just somebody being cute to get attention. It's okay.
quote=krashzmom quote=anotherview This interesti... (
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Ok, Gessman, I'll believe you. (still won't click on it though) :D
quote=gessman quote=krashzmom quote=anotherview... (
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It really is safe. I wouldn't play that kind of trick on you. There's a lot of good info to be gathered and it would be doing yourself a disservice if you failed to take advantage of it just because of the name. A lot is lost in the text version - you need the graphics version to fully appreciate and there are no porn pictures or language for that matter. Here's the text content of the first page. I'm going to remove this in a few minutes but just wanted to leave it on long enough for you to see. I don't want to cause a copyright flap so I'll remove it soon.
Aperture, ISO and Shutter Speed The Good Kind of Threesome
By chl in Howto, Quick Tips Monday December 24, 2007
Canon 24-70mmL, f/2.8, ISO 1600, 0.125s
I thought I would take a little time and whip up an article about some photography basics. Please, please note the use of the word basics in that last sentence. If youre been shooting for any appreciable length of time then youre probably not going to get too much out of this. But given that were smack in the middle of the present giving time of year, its likely that in a few days theres going to be a glut of new DSLR owners out there. What Im aiming for is the article I wish Id found when I first got my camera, to help explain the relationship between three critically important parameters: the ISO speed, aperture (or f-stop number), and shutter speed.
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To lead with, the easiest way I think to approach these three things is to understand physically what they mean inside your camera. So, here we go.
ISO speed: A measurement of how quickly your cameras sensor absorbs light.
Shutter speed: A measurement of how long your cameras shutter is open for when you take a shot.
Aperture: A measurement of how wide the shutter on your cameras lens opens up when you take a shot.
For completeness I should note that ISO speed is not specific to digital cameras with sensors. On film cameras, a particular roll of film will have a specific ISO speed that it is rated for. Fortunately for DSLR users like us, we can change the ISO speed without having to change film. All three of these parameters affect how light gets to your cameras sensor to create an image, so lets start looking at them in more detail.
ISO Speed
The ISO speed changes how quickly the sensor absorbs light. Lower numbers mean less quickly and higher numbers mean more quickly. Now, the thing to keep in mind is that at high ISO speeds, you will introduce some graininess into your image. Therefore, the basic rule of thumb is that you want to shoot at the lowest ISO speed that you can get away with given the environment you are in. For example, if you are outdoors in the middle of a sunny day, you can probably shoot at a very low ISO speed like 100 or 200. Conversely, if you are shooting indoors or at night (or both) you will probably need to shoot at a high ISO speed in order to properly expose your image.
Shutter Speed
This one is probably the easiest of the three to get your head around. Its exactly what it sounds like: the length of time that the shutter is open and light can get in through the lens to your sensor. Shutter speeds on Canon cameras are displayed as inverse numbers against one second. So, if your cameras shutter speed is set to 125, that means that the shutter will be open for 1/125th of a second. Therefore, higher numbers mean that the shutter is open for less time. The effect this has is on the sharpness of the image. If the shutter is open for a very short amount of time, then even if the thing you are shooting is moving you will be able to get a sharp image of it, because it wont have time to move around before the shutter closes again. The downside is that if the shutter is only open for a instant, then not a lot of light can get in to the sensor.
Aperture (or F-Number)
The third and final member of our roster here is the aperture. This is a measurement of how wide the shutter opens up when you take the shot. In terms of the F-Number, it can be a little bit confusing at first. Youll see lenses listed with specs that read like 35mm f/2″ which doesnt mean too much at first, so lets take a look at that. The 35mm part is the focal length of the lens, in this case fixed at 35 millimeters. Now, the f/2″ part means that the ratio of the focal length to the maximum width that the shutter can open up to is 2. Confused? Lets use some real numbers. This is saying that on this 35mm focal length lens, the maximum diameter that the shutter can open up to is 17.5mm. So, the smaller the F-number is, the wider the lens can open up relative to its focal length.
Understanding the effect this has on your image is a little more complex than with the others because two different effects come into play. The first is the depth of field in your shot. Ive personally always thought that the term depth of field is a bit, well, wrong for what its used to describe. In my opinion, a more accurate description would be plane of focus so Im going to run with that. Here we go. Imagine you are taking a picture, and that there is a magical plane of glass somewhere in front of you that is parallel to the front of your lens. Magical because it can pass through other objects, like the ones youre taking pictures of. Everything within the plane of glass will be in focus, and things that are in front of or behind the plane of glass will be blurred. Got that? Good. Now heres the neat trick: the wider your lens opens up when you take the shot (low F-number), the thinner that plane of glass becomes. Conversely, if your lens opens up only a teeny amount (high F-number), then the plane of glass becomes very very thick. So, a very high F-number means that probably everything in your shot will be in focus. A very low F-number means that only a thin plane will be in focus in your shot.
Still not quite making sense? Its a little hard to visualize at first. Fortunately, Ryans taken a great shot at a wide aperture that should help make things clearer.
Canon 100mm macro, f/4, ISO 400, 0.001s
As you can see, with a wide aperture, the caterpillar is in focus but the areas both in front of and behind it are a bit blurred out. This is often used to make objects in the foreground pop into sharp relief by blurring out the background, which is a standard portrait shooting technique shown here.
Canon 50mmL, f/2, ISO 1000, 0.013s
So the first of the two effects is related to which parts of your shot are in focus and which arent. The second again relates to light. The wider your lens opens up, the more light gets in to the sensor. So shooting with a wide open lens can help you in low-light situations. On the other hand, if you have tons of light, then you can shoot with much smaller apertures if you so choose.
Putting it Together
Now you should have a good understanding of what these three numbers are actually doing on your camera. Lets talk a little bit about how the three are interrelated. All three of them share a common trait, namely that they affect how light gets into your camera to produce an image. This is one of the reasons that youll read over and over that lighting is the most important thing in photography. Lets look at a few scenarios, starting with a situation in which you are doing social shooting in very low light. In this case, you will typically want to set your ISO speed very high at something like 1600, and youll want to open your lens up as wide as it will go (low F-number.) Then, you will set the shutter speed as fast as you can get away with while still getting a reasonable exposure. A good rule of thumb for the shutter speed is its the inverse of the focal length of your lens. Meaning, if youre shooting with a 50mm lens, try to have the shutter speed 1/50th of a second or faster. Practically, I get away with a slightly slower shutter speed than this rule dictates all the time, but its a good thing to keep in mind.
Canon 50mmL, f/1.2, ISO 1600, 0.025s
You definitely see the grain here due to the high ISO setting of 1600. Also, youll note that while the subjects left eye is right in focus, her hair over her right shoulder is a bit blurred. This is due to the very wide aperture of f/1.2. The shutter speed was 1/40th of a second, and fortunately she wasnt moving very much so I was able to get a sharp shot. This was despite the fact that there were only a few tea light candles to illuminate this frame.
Lets look at a more extreme kind of shot next. Low light, but where you want a low ISO to avoid the grain, and a reasonably small aperture so things are in focus. If thats the situation you are in, then in order to get enough light into the camera to get the image, you have to have a very, very slow shutter speed.
Canon 17-85mm, f/8, ISO 100, 25s
In the shot above, taken by Ryan, the ISO speed is very low at 100, and the aperture is at f/8. In order to get the exposure correct, the shutter was open for 25 seconds. Obviously, in order to do this effectively, you need to be using a tripod or some sort of stabilizing device to keep the camera still so that the image comes out sharp.
Lets look at one more thats not in such an extreme low-light situation.
Canon 24-70mmL, f/2.8, ISO 100, 0.001s
This photo was taken in the late afternoon when there was a reasonable amount of ambient light out. The ISO speed is set very low at 100 so the image isnt grainy. I have the aperture open quite wide at f/2.8, so Demians head is in focus but the background is nicely blurred out. The shutter speed was 1/1000th of a second in this shot, so I didnt have to worry about movement from Demian or the camera affecting the sharpness of the shot.
Do I really have to worry about all of this?
At this point hopefully you have a better understanding of why these three magic numbers are important for your photography. Nonetheless, you may also be there thinking Seriously? Do I have to worry about all of this stuff all the time? The answer in this day and age is no, you can make the camera do at least some of the work for you.
If youre just getting into your DSLR, youve probably noticed that it has a variety of different shooting modes. When I first started learning about all of this, my more experienced friends advised me to use Aperture Priority mode when taking pictures. I recommend that you do the same. In Aperture Priority mode on my Canon rig, you select an ISO speed and the aperture to use, and the camera will pick out the shutter speed for you. This is convenient because you dont have to constantly readjust the shutter speed as youre trying to get your shots. Theres also a Shutter Priority mode, which Ive barely ever used, and it does more or less the opposite. In that mode, you pick the ISO speed and the shutter speed, and the camera will select the aperture for you. I know that on some cameras like the new Nikon D300 there are modes that will also select ISO speeds for you, but I dont have a rig that has this functionality personally so I dont know too much about how to use it.
At any rate, shooting in Aperture Priority mode is a great way to start out since it lowers the number of things you need to concern yourself with. And you can always see what the camera is recommending for you in the viewfinder, or by looking at the EXIF data later on when youve processed the image. Ive personally been shooting in fully manual mode a great deal as of late, but thats mostly because I keep finding myself in very dark situations and Im generally insistent on getting a sufficiently fast shutter speed so that the shots are clear. That said, for normal daytime shooting, myself and many of my friends use Aperture Priority mode a great deal of the time.
In Conclusion
I hope this serves to clarify some of the jargon that you may be absorbing. Theres definitely a learning curve with photography, but once you get the basics down its an incredibly fun endeavor. If anybody has questions please ask them via comments and Ill do my best to answer them. Happy Holidays!
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ISO Relationships | Elementary Photography
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Amar
on Monday 24, 2007
hey! thank very much for this. you have been a great help. btw when this page was loading i looked in my address bar, i was shocked to see cameraporn.net i.e camera porn thought it was about pornography LOL
Jack
on Monday 24, 2007
Thank you. I just got an S95 and have been trying to figure out how to use it correctly. This article has saved me time and has been very informative. Cheers!
Mike
on Monday 24, 2007
Thanks. Like a previous poster I recently got a Canon S95 and was wondering about this after playing with full manual mode. With all my previous cameras I just used full Auto I love messing with the f-stop and playing with depth of field. Im going to play with the cameras aperture priority mode tomorrow!
GlennG
on Monday 24, 2007
Very Very Enlightening. I was wondering if I could attach a link on my site for this article. It was extremely helpful.
dave
on Monday 24, 2007
I realize this article is a few years old but
Amazing explanation of aperature, iso and shutter speed. Thanks so much for this!
I really like the pane of glass comparison for aperture.
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