ISO, maximum effective
last updated Sunday, June 28, 2015
Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos. Holding all else equal, cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
Read on for more background...
ISO is adjusted by a photographer to ensure a proper exposure: A higher ISO setting increases the sensitivity of a camera's sensor (better for dark scenes), while a lower ISO decreases its sensitivity (better for bright scenes).
Big differences in image quality as ISO climbs
For a number of technical reasons, photos taken at higher ISOs may exhibit more noise (graininess), blurring and/or loss of detail. These factors significantly degrade the quality of a photo. The maximum native (or normal) ISO is the point after which the manufacturer has decided the results would be unacceptable.
Some cameras are better than others
While a given ISO setting on different cameras will yield a similar scene brightness and exposure, the quality of photos taken at this ISO may be very different; some cameras are much better at maintaining good image quality at high ISOs. You can see an example of this difference in our Nikon D3200 vs D5500 image quality comparison page, where you'll notice that the D3200 has more noise in its images at ISO 3200.
Effective ISO attempts to level the playing field
The maximum effective ISO statistic was developed by DxO Mark to evaluate ISO performance equally. DxO set a baseline quality standard for photos and assigns a numeric score for the ISO that yields an equivalent noise and detail level across cameras. You can read more about their standard here.
Interpreting effective ISO
If Camera A and B have effective ISOs of 1600 and 3200, respectively, Camera A would need twice the light as Camera B to capture a photo with similar noise and detail. So if you're shooting in low light, Camera B would be the better choice.
You can still take great photos well above this number
It's important to note that you can still take excellent photos with cameras well above their maximum effective ISO if you're willing to accept more noise in your photos or if you don't intend to make large prints.