The technology of ISO settings on digital cameras replicates the rated speeds of the films of yesteryear. In very general terms, ISO is the sensitivity to light of the sensor in the same way that film speeds were more or less sensitive to light. But there are differences between film and digital sensors; specifically, as the sensitivity setting increases on a digital camera, the output of the sensor is also amplified. This was referred to as grain when we used high-speed films. So, although you have the option of increasing the ISO sensitivity at any point in shooting, the tradeoff in increased amplification or the accumulation of an excessive charge on the pixels is an increase in digital noise. And the result of digital noise is an overall loss of resolution and image quality.
Partly because the 5D Mark II has relatively large pixels on the sensor and because Canon has done a fine job of implementing advanced internal noise-reduction processing, the 5D Mark II stands out as the top performer even at high-sensitivity settings, particularly at exposure times of 30 seconds or less.
In this smart mode borrowed from point-and-shoots, Auto ISO controls the sensitivity of your sensor depending on the Shooting mode you ‘re in. In Full or Creative Auto, P, Tv, or Av, the camera selects between a 100-3200 ISO range. Switch to M, B, or add a Speedlite, and Auto ISO locks in at 400. Auto ISO is shown as an A on the LCD panel when selected and is located at the bottom of the scale by rotating the Main dial counterclockwise after pressing the ISO selection button.
ISO range and Custom Function options
The 5D Mark II offers a wide ISO range, including Auto and settings from 100 to 6400 in 1/3-stop increments or 1/2-stop increments, set by using the options in C.Fn I-01. The ISO range can be expanded to include ISO 50 (shown as L), 12800 (shown as H1), and an incredible 25600 (shown as H2) by setting C.Fn I-03 to On. Be aware that ISO 50 reduces the dynamic range in the highlights by approximately 1 stop, which makes this sensitivity less useful in high contrast light. ISO 50 can be useful in a studio setting by providing flexibility in aperture choice.
With the 5D Mark II, Canon offers an option to reduce or eliminate noise in long exposures.
Using the long-exposure noise-reduction option, available by using C.Fn II-01, noise is totally or virtually eliminated by processing in-camera that ‘s very capable but takes almost as long as the exposure to complete.
Setting the ISO and extended range ISO
To change the ISO setting on the 5D Mark II, follow these steps:
1. Press the ISO selection button above the LCD panel. The current ISO setting appears on the LCD panel and in the viewfinder.
2. Turn the Quick Control dial clockwise to set a higher sensitivity or counterclockwise to set a lower sensitivity. The camera displays the ISO settings as you turn the dial. If you have ISO expansion turned on by using C.Fn II-01, then ISO 50 is shown as L, ISO 12800 is shown as H1, and 25600 is shown as H2. The ISO option you select remains in effect until you change it again.
To turn on ISO expansion, follow these steps:
1. Press the Menu button and then tilt the Multi-controller until the Custom Function (orange) menu appears.
2. Press the Set button. The Custom Function screen appears, and the Custom Function number control in the top-right corner of the screen is activated.
3. Turn the Quick Control dial to set the C.Fn I number to 03 and then press the Set button. The ISO expansion control is activated.
4. Turn the Quick Control dial clockwise to select option 1: On and then press the Set button. ISO expansion remains turned on until you change it.