Why don't most digital cameras offer ISO settings below about 80 or 100?
Asked 2/25/2011
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Digital cameras often start at a minimum ISO around 80, 100, or 200. Since higher ISO is achieved by adding gain to the sensor signal, why can't cameras simply be made less sensitive to light and offer much lower ISO settings? What limits the minimum ISO on a digital sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
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If a manufacturer wanted to do that, they could.
That being said, all sensors have a native sensitivity, usually ISO 100, 160 or 200. Gain is used to achieve higher sensitivities by multiplying the base signal. This introduces more noise, so if the base ISO was lower, them you would need to use more gain to achieve higher sensitivities and you would get more noise.
To get lower ISOs without changing the base setting, you basically divide the base signal. This causes a reduction in dynamic range, which is why you rarely see ISOs less than 50. If the base ISO would be divided by a larger factor, then too much dynamic range would be lost.
Finally, there is not much reason to develop lower sensitivity sensors since it is easy to use an ND filter to reduce incoming light without affecting dynamic range. Several cameras from Canon, Nikon and Fuji have a 2 or 3 stops ND filter built-in for that effect. On a DSLR, you can buy ND filters with variable strength which makes things very flexible.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
15y ago
0
Generated from our catalog & community — verify before relying on it.
A camera sensor has a native or base sensitivity, often around ISO 100, 160, or 200. Higher ISO is created by amplifying that base signal, which adds noise. Lower-than-base ISO usually is not the sensor becoming truly less sensitive; it often means reducing or scaling down the recorded signal, which can reduce dynamic range.
Making a sensor genuinely lower in sensitivity is possible, but it usually means tradeoffs. One way is to make it less efficient at capturing light, which is generally undesirable. Another is increasing pixel well capacity so each pixel can hold more charge before clipping, but that is a sensor-design challenge rather than just a setting.
In practice, very low ISO is not offered much because it has limited benefit for most photographers, while lower-than-base settings can compromise image quality. When there is too much light, photographers typically use faster shutter speeds, smaller apertures, or ND filters to cut light before it reaches the sensor. That preserves image quality better than forcing an artificially low ISO.
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