Dual Native ISO

Dual native ISO is a sensor design with two amplifier circuits, each with its own base ISO. The first base, often ISO 100 to 200, gives the widest dynamic range in bright light. The second base, often ISO 640, 800, or higher, switches on in dim light and lowers read noise again. Between the two the camera amplifies the first circuit, so noise rises until the second circuit takes over. It is also called dual gain or dual conversion gain.

Base ISO is the single lowest standard setting on any camera, where the sensor records its widest dynamic range. Dual native ISO describes a sensor that has two such settings instead of one. The first is the ordinary base ISO. The second is a higher value where a separate circuit takes over and read noise drops back down. Every camera has a base ISO; only cameras with two gain circuits have a second one.

It depends on the sensor. Common values are ISO 640, 800, 1250, 1600, and 2500, and some video cameras place it as high as ISO 12800 in a log profile. Manufacturers usually publish the two values for video log profiles, since video makers rely on them. For stills the easiest way to find the value is a camera review site that charts read noise per ISO; the second base appears as a sudden drop.

Right below the second base the camera is still using the first circuit, pushed to its limit. At the second base a fresh circuit takes over with lower read noise. So a frame at ISO 500 on a camera that switches at 640 can show more shadow noise than a frame at 640. This only happens around the switch point. Above the second base, each higher ISO adds noise in the usual way.

No. The second circuit trades some highlight capacity for lower noise, so dynamic range at the second base is usually about a stop below the first base. That is still better than the step right below the switch, where the first circuit has been amplified several times. In bright light the first base remains the best choice. The second base wins once the light is too dim for the first base to work.

No. Video makers notice it most because log profiles list the two bases and dim indoor scenes are common in video work. Still photographers benefit in the same situations: concerts, weddings, indoor sports, night streets, and wildlife at dusk. Knowing the second base lets a photographer pick the cleaner setting in dim light instead of sitting one stop below it.

Auto ISO picks the lowest ISO that keeps the shutter speed above its floor. It does not know where the second gain circuit begins, so it can land one stop below the switch, which is the noisiest spot on the curve. For a long low-light session it is better to set ISO by hand at the second base and let the shutter speed or aperture handle small changes in light.

Yes. The switch between circuits happens in the sensor before the RAW file is written, so a RAW frame at the second base holds cleaner shadows than one taken a step below it. Brightening the darker frame in editing does not recover the difference, because the extra read noise is already in the data. This is one case where choosing the ISO in camera matters more than the ISO slider in editing.

Check the video section of the camera manual, where log profiles often list both base ISOs. If the manual is silent, camera review sites publish read-noise and dynamic-range charts per ISO, and the second base appears as a sudden drop in noise. The quickest home test is to shoot the same dark scene at every ISO between the first base and ISO 3200, then compare the shadows at full size.

No. Many sensors use a single gain circuit, and noise simply rises step by step from the base ISO. Dual gain designs appeared in video cameras first and have spread to many mirrorless bodies from Sony, Panasonic, Nikon, Fujifilm, and Canon, but each model differs. Older DSLRs and many compact cameras do not have it. The camera manual or a read-noise chart confirms whether a given model does.