When is high ISO useful, and does it improve camera performance?
Asked 5/27/2011
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I’m learning photography and want to understand when using a high ISO is actually helpful. My camera only goes up to ISO 800, while some newer cameras advertise very high maximum ISO values like 64,000. In what situations is high ISO useful, and can it be used creatively for any special effect? Also, does a higher maximum ISO indicate better real-world performance?
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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ISO is very useful as it helps overcome read noise by amplifying a weak analogue signal prior to digitization (which adds a more or less constant amount of noise) thus giving a better signal to noise ratio.
That's all raising the ISO does, amplify the signal. It does not make the picture noisier because it only amplifies what's already there.
See this example. The ISO100 shot was significantly underexposed and suffers from really bad read noise. The same amount of light enters the camera in the second shot, but due to ISO the signal is amplified before readout, thus read noise is a smaller percentage of the signal and overall signal to noise ratio is better:
To using a high ISO actually helps to reduce noise when you have a limited amount of light (and you can't get any more by opening the aperture or shutter for longer).
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
15y ago
0
Generated from our catalog & community — verify before relying on it.
High ISO is useful when you need a faster shutter speed or can’t add more light by opening the aperture, slowing the shutter, or using flash. Common examples are low-light shooting, indoor events, journalism, and freezing fast action.
Raising ISO doesn’t make the sensor collect more light; it amplifies the captured signal. In low light, that amplification can help reduce the impact of read noise compared with badly underexposing at a lower ISO and brightening later. The tradeoff is that very high ISO usually gives less image quality overall than capturing more light would.
A higher maximum ISO can be helpful, but it doesn’t automatically mean better image quality. What matters is whether the camera produces acceptable results at those settings. Some cameras handle ISO 800 very well; others remain usable much higher.
For creative effect, high ISO can introduce visible grain/noise, though many photographers don’t find color noise attractive and prefer to add any grain effect later in post-processing.
So yes, high ISO is genuinely useful—mainly as a practical tool to get the shot when light or shutter-speed limits leave no better option.
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