Here is what I think I know.... The lower the ISO the better the photo quality...The higher the ISO the grainer the photo. Is this correct?
Now time for school.
What is the relationship between ISO, shutter speed, and apature?
Posted by Rod Barbee on January 4, 2008 at 2:42 PM
You're essentially correct on the ISO. For an explanation of how it all works together, take a peak at this Back to Basics series I've been working on.
Posted by Doug Andrews on January 4, 2008 at 2:47 PM
Yes to your first question.
As to your second question. Maybe if you think of ISO, shutter speed, and aperture in terms of water coming out of a spigot. The proper exposure would be analogous to filling a glass of water. Aperture would be analogous to how much the spigot is opened, shutter speed to how long the spigot is open, and ISO to a filter on the spigot removing impurities or in photo terms, noise. Just cracking the spigot open (smaller aperture opening) means you have to leave it open longer (slow shutter speed) to completely fill you glass of water. Opening it all the way (wide aperture) means it only needs to be open for a short time (fast shutter speed) to fill the glass. The better the filter is at removing impurities/noise (lower ISO), the longer you'll have to leave the water running (slower shutter speed) as a finer filter slows down the water flow more than a more porous one that lets through more impurities/noise. Hope I haven't confused you with this.
Posted by David Bostedo on January 4, 2008 at 4:36 PM
The lower ISO rule is generally true Kevin. Some cameras, however, don't see a benefit from going too low, and actually lose some ability to capture a large dynamic range. For instance, Canon pro series are best at ISO 100, even though you could shoot at ISO 50. (ISO 100 might have more noise, but it's so low as to be unnoticable.)
Rod - One thing that you might want to note (and I apoligize if you have it in there) is that you are treating ISO separately from aperture and shutter speed. I wonder if this is a holdover from the inconvenience of changing ISO with film? Anyway, I think of exposure as being controlled by three things : ISO, shutter speed, and aperture. They can all be modified together to create proper exposure. I don't know that most "new" shooters, or digital shooters, think of ISO as all that separate, since it's so easily changable. (Of course, that's just how I think of it - I'm sure there are myriad ways...)
Posted by Basil Greber on January 4, 2008 at 5:28 PM
Yes to your first question. As I always do when my girlfriend asks this, I refuse to answer your second question. Try it. You learn much more by trying than by reading answers. Just MHO.
David makes an excellent point. I am guilty of rarely changing the ISO simply because my habits were established BD (before digital). I have finally managed to stop pressing the shutter release twice (no need for in-camera dupes now), but I often overlook an opportunity to crank up the ISO. There are cases where you might do better by accepting more grain/noise to gain sharpness. A recent case of this I can recall is a fog image where I had the point & shoot on fool-auto mode and it maxed out the ISO, but the result was quite ok. If I were using a dSLR I would almost certainly have been shooting at ISO 200 (on a tripod), but this case subject movement (dang humans) probably would have ruined the shot.
As to the relationship of f-stop, shutter speed and ISO, there are better 'splainers out there than me. Just remember, life is just a series of compromises.
Pete D.
Posted by Dan Borzynski on January 4, 2008 at 6:04 PM
Three things determine correct exposure: shutter speed, aperature size and ISO. Before digital, ISO was known as the film speed. ISO/film speed essentially measures the sensitivity of the recording medium, whether it is film, digital sensor or even photographic paper.
Under clear blue skies, midsummer, little pollution and in an obscure location in Great Britain, the following is a correct exposure combination when pointed at the blue sky:
ISO or film speed: 100
Shutter speed: 1/100 sec (or 1/125 which is probably what your camera gives)
aperature: f16
Why the Great Britain comment? I have this vague recollection that the standard was actually developed somewhere out in the british countryside. Actually, it really doesn't matter too much since almost any point in populated areas of North America and Europe will (or at least should) give the same result. Due to things like pollution, light clouds, and not pointing the camera in exactly the right way, it may well give a different result, but that is the theory...
Okay, so what happens if you want to shoot at 1/500 of a second? To get a proper exposure, you need to do one of two things. First, since the shutter is open for less less, you need to get more light to the recording medium. 1/125 sec to 1/500 second is two stops:
1/125 -> 1/250 -> 1/500
So open up the aperature two stops:
f16 -> f11 -> f8
So the new exposure is 1/500 sec at f8 with ISO at 100.
Or what you could do is increase the sensitivity of the recording medium. We started at ISO 100, or with 100 speed film. We need two more stops of sensitivity.
ISO 100 -> ISO 200 -> ISO 400 (as the numbers increase, sensitivity increases like stops)
So the new exposure is
1/500 second, f16, ISO 400
Or we could do one of each: Open up on stop in aperature and one in sensitivity
ISO 1600, ISO 800, ISO 400, ISO 200, ISO 100, ISO 50, ISO 25
As you go from left to right on all three of these, you will need to add more stops of light in some form to get a proper exposure.
Starting with your base exposure, if you change one of the numbers above by n stops, you need to change the other two by a total of n stops. In the above example, I changed the shutter speed by 2 stops less light, so I had to add two stops of light by getting it from the aperature (first example), ISO or film speed (second example), or by one of each (third example).
A large ISO like 800 allows you to have a faster shutter speed like 1/500 or smaller aperature like f16.
A small ISO like 100 means a slower shutter speed like 1/125 second or larger aperature like f8.
(all other things being equal)
ISO is a measurement of a film's sensitivity to light. In digital cameras the film is replaced by the sensor but the light sensitivity is the same. For example, set your digital camera to ISO 400 is the same as having ISO 400 film in a camera. The numbers follow a pattern. ISO 200 needs only half the amount of light to form an image than ISO 100. ISO 400 needs only half the amount of light than ISO 200. So, for example, if your camera is set at ISO 100, f.8, 1/125 and you want to increase your shutter speed from 1/125 to 1/250 without changing the aperture then you set the ISO to 200. Increase the shutter speed to 1/500 you'd set the ISO to 400.
Thanks for all the input.... here is what got me thinking about this.
The other day I went out with my new Sigma 50/500 and a 2x which should give me 1000mm. I was shooting birds from my car. I was primarily going after Hawks on phone poles, Great Blue Herons in ditches and ducks in flooded fields.
I had the car OFF..... and every shot I took had to be sent to the trash can. Every single one was either extrememly soft or just out of focus.... I had the lens mount resting on the door to cut down on camera shake.... I think the ISO on my D80 is currently set to 100.
IF I set the ISO to either 200 or maybe 400 would that in turn increase the shutter speed and help with the quality of the photos. I know that at that focal length any slight movement has a outcome on the photos so I think I need to get a higher shutter speed. I had some excellent shots.... if they would have been in focus.
Posted by David Bostedo on January 4, 2008 at 8:02 PM
Kevin - Every one stop increase in ISO (100->200, 200->400, etc) will let you increase the shutter speed by one stop, which doubles the shutter speed. This assumes the aperture stays the same. Or you could open the aperture, keeping the ISO the same; Or you could do both.
So if you look at the images you took, and check the shutter speed, you can get an idea of what shutter speed would have been possible. For instance, if your image is at these settings :
ISO 100, f/5.6, 1/100s
you could get the same exposure at
ISO 200, f/5.6, 1/200s
or
ISO 400, f/5.6, 1/400s
or
ISO 200, f/4.0, 1/400s
or
ISO 400, f/4.0, 1/800s
They will all give approximately the same exposure, but with slightly different noise characteristics and depth of field.
Given that you were shooting at 1000mm, though, you might be seeing camera shake.If the lens isn't stabilized, you're going to need shutter speeds 1/1000 or faster to get many sharp shots handheld. With some support, like your car window, you could go quite a bit slower. Better still would be a bean bag, or some sort of tripod/monopod support.
Posted by Kent Staubus on January 4, 2008 at 8:27 PM
I don't see any way you are going to get usuable shots putting a teleconverter on a big zoom lens like a Sigma 50-500mm. There are three reasons:
1) Image quality from the lens just isn't there to start with
2) At an effective aperature of >f11 it's going to be too dark to even focus
3) Even using a solid first class tripod & ballhead you aren't going to freeze out all the tiny vibrations.
Hate to be the one to tell you, but you wasted your $$ buying the 2x. No way it's going to work on that lens.
As for ISO, I routinely shoot my D80 at ISO 800. I've never had a magazine turn down a photo because of that. Many of my photos this time of year are taken at night, and I will even use ISO 1600 when I have to.
Discussion
12 repliesNow time for school.
What is the relationship between ISO, shutter speed, and apature?
As to your second question. Maybe if you think of ISO, shutter speed, and aperture in terms of water coming out of a spigot. The proper exposure would be analogous to filling a glass of water. Aperture would be analogous to how much the spigot is opened, shutter speed to how long the spigot is open, and ISO to a filter on the spigot removing impurities or in photo terms, noise. Just cracking the spigot open (smaller aperture opening) means you have to leave it open longer (slow shutter speed) to completely fill you glass of water. Opening it all the way (wide aperture) means it only needs to be open for a short time (fast shutter speed) to fill the glass. The better the filter is at removing impurities/noise (lower ISO), the longer you'll have to leave the water running (slower shutter speed) as a finer filter slows down the water flow more than a more porous one that lets through more impurities/noise. Hope I haven't confused you with this.
Rod - One thing that you might want to note (and I apoligize if you have it in there) is that you are treating ISO separately from aperture and shutter speed. I wonder if this is a holdover from the inconvenience of changing ISO with film? Anyway, I think of exposure as being controlled by three things : ISO, shutter speed, and aperture. They can all be modified together to create proper exposure. I don't know that most "new" shooters, or digital shooters, think of ISO as all that separate, since it's so easily changable. (Of course, that's just how I think of it - I'm sure there are myriad ways...)
Basil
As to the relationship of f-stop, shutter speed and ISO, there are better 'splainers out there than me. Just remember, life is just a series of compromises.
Pete D.
Under clear blue skies, midsummer, little pollution and in an obscure location in Great Britain, the following is a correct exposure combination when pointed at the blue sky:
ISO or film speed: 100
Shutter speed: 1/100 sec (or 1/125 which is probably what your camera gives)
aperature: f16
Why the Great Britain comment? I have this vague recollection that the standard was actually developed somewhere out in the british countryside. Actually, it really doesn't matter too much since almost any point in populated areas of North America and Europe will (or at least should) give the same result. Due to things like pollution, light clouds, and not pointing the camera in exactly the right way, it may well give a different result, but that is the theory...
Okay, so what happens if you want to shoot at 1/500 of a second? To get a proper exposure, you need to do one of two things. First, since the shutter is open for less less, you need to get more light to the recording medium. 1/125 sec to 1/500 second is two stops:
1/125 -> 1/250 -> 1/500
So open up the aperature two stops:
f16 -> f11 -> f8
So the new exposure is 1/500 sec at f8 with ISO at 100.
Or what you could do is increase the sensitivity of the recording medium. We started at ISO 100, or with 100 speed film. We need two more stops of sensitivity.
ISO 100 -> ISO 200 -> ISO 400 (as the numbers increase, sensitivity increases like stops)
So the new exposure is
1/500 second, f16, ISO 400
Or we could do one of each: Open up on stop in aperature and one in sensitivity
f16 -> f11
ISO 100 -> ISO 200
So the new exposure will be
1/500 sec, f11, ISO 200
It is best to think of things in stops:
1 sec, 1/2 sec, 1/4, 1/8, 1/15. 1/30, 1/60, 1/125. 1/250, 1/500, 1/1000, 1/2000
f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32
ISO 1600, ISO 800, ISO 400, ISO 200, ISO 100, ISO 50, ISO 25
As you go from left to right on all three of these, you will need to add more stops of light in some form to get a proper exposure.
Starting with your base exposure, if you change one of the numbers above by n stops, you need to change the other two by a total of n stops. In the above example, I changed the shutter speed by 2 stops less light, so I had to add two stops of light by getting it from the aperature (first example), ISO or film speed (second example), or by one of each (third example).
A large ISO like 800 allows you to have a faster shutter speed like 1/500 or smaller aperature like f16.
A small ISO like 100 means a slower shutter speed like 1/125 second or larger aperature like f8.
(all other things being equal)
I hope this helps.
Will
Edmonton, Alberta
Canada
The other day I went out with my new Sigma 50/500 and a 2x which should give me 1000mm. I was shooting birds from my car. I was primarily going after Hawks on phone poles, Great Blue Herons in ditches and ducks in flooded fields.
I had the car OFF..... and every shot I took had to be sent to the trash can. Every single one was either extrememly soft or just out of focus.... I had the lens mount resting on the door to cut down on camera shake.... I think the ISO on my D80 is currently set to 100.
IF I set the ISO to either 200 or maybe 400 would that in turn increase the shutter speed and help with the quality of the photos. I know that at that focal length any slight movement has a outcome on the photos so I think I need to get a higher shutter speed. I had some excellent shots.... if they would have been in focus.
So if you look at the images you took, and check the shutter speed, you can get an idea of what shutter speed would have been possible. For instance, if your image is at these settings :
ISO 100, f/5.6, 1/100s
you could get the same exposure at
ISO 200, f/5.6, 1/200s
or
ISO 400, f/5.6, 1/400s
or
ISO 200, f/4.0, 1/400s
or
ISO 400, f/4.0, 1/800s
They will all give approximately the same exposure, but with slightly different noise characteristics and depth of field.
Given that you were shooting at 1000mm, though, you might be seeing camera shake.If the lens isn't stabilized, you're going to need shutter speeds 1/1000 or faster to get many sharp shots handheld. With some support, like your car window, you could go quite a bit slower. Better still would be a bean bag, or some sort of tripod/monopod support.
1) Image quality from the lens just isn't there to start with
2) At an effective aperature of >f11 it's going to be too dark to even focus
3) Even using a solid first class tripod & ballhead you aren't going to freeze out all the tiny vibrations.
Hate to be the one to tell you, but you wasted your $$ buying the 2x. No way it's going to work on that lens.
As for ISO, I routinely shoot my D80 at ISO 800. I've never had a magazine turn down a photo because of that. Many of my photos this time of year are taken at night, and I will even use ISO 1600 when I have to.
Kent in SD
Great topic! You aren't the only one to get educated!