Exposure (2) ISO + Intro to Aperture

[RichardTaylor]

ISO shutter speed and aperture.

ISO is the sensitivity setting for the camera. The higher the ISO the more sensitive the camera is to light allowing you to;
(1) shoot with less light,
and/or
(2) Shoot with a faster shutter speed to reduce camera and subject motion,
and/or
(3) Shoot with a smaller aperture (higher F number) to give you deeper zone of sharpness in your photograph, ie Depth of Field (more to come on this).

The main downside with shooting at high ISO is that the pictures become noisy, ie "gritty", and may become soft if the camera applies noise reduction.

# 1
Here is an example of ISO 80 and ISO 3200 straight out of a point & shoot camera. (100% crops)



However whilst I prefer to use the lowest possible ISO, if need be I will use what ever ISO is needed to achieve a reasonable photograph.
I feel it is better to have a noisy image rather than an underexposed or blurred image. Here is an example at ISO 3200 on a DSLR and selective noise reduction, and sharpening, applied when I was post processing the RAW file (ie the camera did not apply any unwanted processing to my picture)

#2

Camera Canon EOS 40D
Exposure 0.005 sec (1/200)
Aperture f/2.0
Focal Length 135 mm
ISO Speed 3200
Exposure Bias 0 EV
Flash Off, Did not fire

---------------------------------------------------

Introduction to Aperture.

Beside controlling the amount of light through the lens the aperture also controls the zone of sharpness, depth of field (DOF) in the photograph. DOF is also dependant on shooting distance to the subject, camera type and lens focal length (eg wide angle, normal or telephoto).

The wider the aperture (smaller F numbers) the less DOF.
The smaller the aperture (large F numbers) the more DOF.

#3 An example of shallow DOF. Notice only the man's head is sharp.

Camera Canon EOS 40D
Exposure 0.001 sec (1/1000)
Aperture f/2.0
Focal Length 135 mm
ISO Speed 400
Exposure Bias 0 EV
Flash Off, Did not fire
Subject Distance 5.8 m

#4 An example of a lot of DOF.

Camera Canon EOS 5D
Exposure 0.008 sec (1/125)
Aperture f/10
Focal Length 24 mm
ISO Speed 100
Exposure Bias 0 EV

More to come on aperture.

-------------------------------
The main thing to remember it is a "balancing act".

ISO, shutter speed and aperture all work together and normally if you change one you change the other.
--------------------------------------

This series

# 1 Introduction to exposure
Exposure (1) A balancing act

#3 Aperture.
Exposure (3): Aperture

#4 Shutter Speed.
Exposure 4: Shutter speed.

#5 Putting it all together
Exposure 5: Putting it all together

Future posts in this series will include more detail on;
White balance
Exposure compensation

Thanks for looking.
Feel free to ask questions and feedback would be appreciated.

Richard

[Krusty79]

Well, you're getting a lot of views, but no one seems to want to comment. Since I mainly shoot landscapes, I use 100 ISO to minimize grain. If you shoot at a high ISO, can you offset much of the noise with a program like Topaz or Noise Ninja?

[RichardTaylor]

Thanks.

Yes you can. I use Topaz Denoise, but only when needed.
However it does so by blurring the image. The more noise reduction you apply the more the image becomes blurred. You can select where you want the noise reduction and the amount by using layer masks when PPing.

[Eastree]

The issue with noise removal software is to be careful; it can seriously reduce sharpness in the image. At least the general advice I've read is to be careful not to denoise enough to be unable to recover details.