Wednesday, April 21, 2010

Exposure: Light, Aperture, Shutter Speed, and ISO - Part 3 - ISO

In the previous articles, we talked about aperture (f/stops) and shutter speed. We're now going to finish the basics of exposure by talking about ISO.

What we're really talking about is the sensor in the digital camera. It's make up of millions of microscopic pixels crowded into a couple of square centimeters of space, if that.



ISO (at least in a photography context) is the measurement of how sensitive the sensor is to light. The higher the number, the more sensitive.

And happily, that measurement actually goes in the right direction, as opposed to the confusing f/stops and shutter speeds that we talked about in the previous articles. The ISO actually increases with the sensor's sensitivity. You'll see digital cameras starting with an ISO as low as 50 and increasing from there.

50
100
200
400
800
1600
3200
6400
12800
25,600
51,200
102,400

As with f/stops and shutter speeds, the doubling of the number indicates one full f/stop change in the exposure. So going from ISO 400 to 800 would be the equivalent of increasing the exposure by one f/stop - just like going from f/8 to f/5.6

In other words, by lowering the f/stop, we let more light through the aperture. Or, we can simply double the sensitivity of the sensor by raising the ISO.

There are some problems though. As you increase the ISO and raise the sensitivity of the sensor, you get more "noise." Think of it as grain or visual static.

This image was taken at an ISO of 200

Image2

This was taken at 6400

Image1

Notice that the second one shows more noise, particularly in the center along the edge of the tape. If you want to see it even more clearly, click through the pictures and look at the larger versions on Flickr.
Is Everybody Happy?!?!
What causes noise? There are some technical explanations, but allow me to use a metaphor. When you raise the ISO of a sensor, you're making all of those individual little pixels work harder to capture the light. Just like any crowded group of workers, they're bumping into each other more, jostling, yelling, getting into fights, etc. In other words, as they work harder, they make more noise. As you make the sensor work harder by making it more sensitive to light, it makes more noise.

Noise means that you need to consider whether increasing the ISO and getting more noise is worth it for the picture you're trying to take. Happily with today's cameras, the manufacturers are getting better and better of controlling that noise problem.

So there you have it. There are basically three elements that control your exposure.

fstops700

The aperture controls the amount of light passed through the lens. It's measured in f/stops which increase as the amount of light let through is decreased.

The shutter opens to allow the light from the aperture to pass to the sensor. It controls the exposure by only letting the light in for a specific amount of time. It's measured in fractions of a second.

And the sensor's sensitivity to light is measured by its ISO. As the ISO goes up, the sensor becomes more sensitive.

Correctly balancing these three elements leads to the right exposure for your picture.

By the way, ISO is the short name of the for the International Organization for Standardization, in case you're vaguely interested.



Jim Frazier

Take one of my photography classes!
http://www.jimfrazier.com/photography-classes/index.htm

COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.












Monday, April 19, 2010

Three Pictures

UP 4437 Westbound
UP 4437 Westbound
Rochelle Railroad Park www.rochellerailroadpark.org/
Rochelle, Illinois
April 2010

Japanese Tree Lilac
Japanese Tree Lilac
Syringa reticulata
Cantigny Park, Wheaton, Illinois
April 2010


Cantigny Park, Wheaton, Illinois
April 2010

Take one of my photography classes!
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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Friday, April 16, 2010

Sunset Through The Window

Sunset Through The Window

I drove past this building (the old Challenge plant) and noticed that the sunset was shining right through the building from one window to the other window. I had to stop. That's a phenomenon you just don't see very often.

Batavia, Illinois
April 2010

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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Tuesday, April 13, 2010

Exposure: Light, Aperture, Shutter Speed, and ISO - Part 1 - Aperture

In the next couple of posts, I'm going to try to explain how light, aperture, shutter and ISO combine to give you the right exposure for your pictures.

Here's how the system works:

fstops700

Light comes into your lens, reflected from the surface of your subject.

Your lens focuses the light.

Inside the lens is a diaphragm.

diaphragm
Picture by Mohylek (Creative Commons License)

The diaphragm is adjustable allowing you to control the aperture that the light passes through. Can you see that the aperture is bigger in the top picture? That means that more light is passing through the diaphragm on its way to the sensor.

When we're talking about the size of that aperture, we use the term f/stop. The number is the ratio of the diameter of the aperture to the focal length of the lens. For example, if we had a lens that had a focal length of 100mm, and the aperture had a diameter of 50mm, then the ratio would be 1/2. The f/stop would be f/2.

If the f/stop was f/8 on that 100 mm lens, then the diameter of the aperture would be 1/8 of the focal length.

(By the way, "focal length" means the optical length of the lens. In the old days, you actually could measure a lens with a ruler and come pretty close to knowing its "focal length".)

So the confusing part is that, as the f/stops values go up, it means that the size of the aperture gets smaller and the amount of light getting through goes down.

diaphragm2
picture by Chris Buckley (Creative Commons License)

This sequence shows, in photographs, how an aperture that is decreasing in size results in less light getting through.

For mathematical reasons that are beyond me, the volume of light passed through is halved every time you go "up" one full f/stop. So, f/2.8 allows half of the light as f/2.0. We went "up" a full f/stop when we went from f/2.0 to f/2.8.

This chart shows how the amount of light is decreased as the f/stops increase in "full" f/stops.
progression1

This is known, by the way, as "stopping down." The f/stop numbers are going up, but you're reducing the amount of light passing through the lens.

To complete the confusion, if I'm going from f/2.8 to f/2.0, I'm doubling the amount of light that is passing through the lens. The f/stop numbers went down, but the amount of light went up. This is known as "opening up."

Here's the summary:

Aperture, which is measured by f/stops, controls the volume of light passing through your lens.

As the f/stop number increases, the aperture gets smaller and the volume of light is reduced.

As the f/stop number decreases, the aperture gets bigger and the volume of light is increased.

And the f/stop number is really a fraction showing the ratio of the aperture to the focal length of the lens.

That's really all you need to remember about aperture for now.

Next, we'll talk about shutter speeds.


Jim Frazier

Take one of my photography classes!
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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Monday, April 12, 2010

It came from outer space....

It came from outer space....

found in Wheatfield, Indiana
April 2010

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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Friday, April 9, 2010

Oh, dear. It's the paparazzi again. Now I know how George Clooney feels. ;-)

Oh, dear.  It's the paparazzi again.  Now I know how George Clooney feels.  ;-)

These guys from the local newspaper were taking pictures to illustrate a story about me that was supposed to run yesterday. It may run next week, but who knows. At least I got a shot of THEM.

Fabyan Forest Preserve
Geneva, Illinois
April 2010
frazier-jim-100401e-DSC_9944a-wb

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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Tuesday, April 6, 2010

Cantigny on Fire

Cantigny on Fire

The annual spring prairie burn at Cantigny Park, Wheaton, Illinois on April 1, 2010.
frazier-jim-100401c-DSC_9799a-wb

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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Fresh Magnolia

Fresh Magnolia

These babies had just come out. It seems to me that Magnolias practically bloom with brown edges, so I was thrilled to not only get really fresh ones, but also find a couple with beautiful centers.

Cantigny Park, Wheaton, Illinois
April 2, 2010
frazier-jim-100402d-DSC_0012b-wb

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COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See www.jimfrazier.com for more information.

Saturday, April 3, 2010

TEB Takes Five

TEB Takes Five

The Easter Bunny (or as we called him - "the") takes a short break from posing for pictures at Cantigny's "Breakfast with the Easter Bunny" and the Easter Egg Hunt.

I photographed 147 different groups of really cute kids (and some adults) between 9am and 12:30 pm. It was a blast.

Some of the kids were terrified of the big white rodent, others couldn't get enough of him. There was one little girl that was literally trembling with excitement. She would stand away from him, then edge a little closer, then TEB would hug her. It was just adorable.

Lighting: SB600 through large umbrella high and camera right at 1/2 power. SB600 in Lastolite Ezybox directly in front of camera and below at 1/8 power. Both triggered by CLS. This configuration solved a problem I was having in previous events where one child would cast a shadow on another kid. The umbrella camera right was 46 inches, so it threw some big light, but the softbox filled in any problem shadows. It even dealt with a few kids (and dads) wearing hats. I love it when a plan comes together.

Cantigny Park, Wheaton, Illinois
April 3, 2010

frazier-jim-100403c-DSC_0359a-wb



COPYRIGHT 2010 by Jim Frazier All Rights Reserved. This may NOT be used for ANY reason without consent. See JimFrazier.com for more information.

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