What does 'expanded ISO' mean, and how does it affect image quality?
Asked 10/19/2010
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2 answers
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Some cameras list a standard ISO range and then additional settings such as "expanded ISO," "H," "Hi1/Hi2," or low expanded values like ISO 50. For example, the Canon EOS 7D lists ISO 6400 as standard and ISO 12800 as expandable, while some Nikon models label settings above the normal range as Hi modes.
What makes an ISO setting "expanded" rather than part of the normal range? Does it require enabling a menu option, or is it simply a manufacturer warning about image quality?
How are expanded high and low ISO settings typically implemented, and what are the practical effects on noise, dynamic range, color, and highlight clipping? Is it generally better to use these settings in-camera or shoot RAW and apply the equivalent exposure adjustment later?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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There are two reasons why an ISO is not made part of the 'normal' range:
It is considered a non-trivial drop in quality and you do not want users complaining about its performance. In other words, if the quality difference between ISO 12800 and 6400 is stronger than the one from 3200 to 6400. Note that there may be more changes than simply more noise, colors can be affected as well.
The camera meters and exposes for the said ISO, say 12800, but the results do not strictly comply with the ISO standard. When that happens, you will notice that the ISO is NOT stored in the EXIF of the image. This usually happens because of a drop in dynamic-range at the expanded setting.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
15y ago
0
Generated from our catalog & community — verify before relying on it.
"Expanded ISO" usually means the setting is outside the camera’s normal, manufacturer-recommended range. It doesn’t require extra hardware; often you just enable it in a menu.
Why it’s labeled separately:
- Image quality drops more noticeably than within the standard range.
- It may not meet the maker’s normal ISO-performance or ISO-standard expectations.
- Some expanded settings are done digitally rather than by true analog gain.
Expanded high ISO:
- Often similar to underexposing and brightening later.
- Typically brings more visible noise, reduced dynamic range, and possible color degradation.
- Because of that, many photographers prefer to shoot RAW at the highest normal ISO and adjust in post if needed.
Expanded low ISO (like ISO 50):
- Usually not the sensor becoming "less sensitive."
- Often achieved by overexposing relative to the camera’s native/base ISO and then pulling brightness down.
- This can reduce highlight headroom and cause clipping sooner, so it’s usually not better for image quality.
Bottom line: expanded ISOs are best treated as emergency or convenience settings, not optimal-quality settings. Use them when you need a certain shutter speed/aperture in-camera, but expect compromises.
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