What is dual native ISO?

A dual-native-ISO sensor has two analogue conversion-gain circuits, each with its own optimised clean point. The low base, like 640 on a Sony FX3, gives the cleanest image in good light, while the high base, like 12800, gives a second clean point for low light without simply amplifying noise from the low base.

Which native base should I use for a given ISO?

Use the highest native base that is at or below your target ISO, because amplifying upward from a native base is cleaner than sitting between bases. Below the midpoint between the two bases the low base is usually cleaner; above it the high base takes over, which is exactly what this tool computes.

Does changing ISO change my exposure?

ISO itself only amplifies the signal already captured by the shutter and aperture, so changing ISO at fixed shutter and aperture changes image brightness, not the light hitting the sensor. To switch native bases while keeping the same brightness you compensate with shutter or aperture, which the tool quantifies in stops.

Why not just always shoot the high native ISO?

The high base sacrifices highlight headroom and is noisier than the low base in good light. The low base delivers the camera's full dynamic range when there is enough light, so you choose the base that matches your scene brightness rather than defaulting to the high one.

Is the noisy region really between the two bases?

Yes. ISO values that sit between the two native bases are produced by amplifying the lower base, so they carry more noise than either base point. Whenever practical, set exposure so your working ISO lands on or just above a native base for the cleanest result.

Dual Native ISO Equivalence Calculator

Cameras with dual native ISO have two sweet spots, not one. Knowing which base to sit on — and how to keep your exposure looking identical when you switch — is the difference between a clean file and a noisy one. This tool picks the cleaner native base for your target ISO and tells you exactly how to compensate shutter or aperture.

How it works

A dual-native sensor has two analogue gain circuits, each with its own clean point: a low base (for example ISO 640 on a Sony FX3) and a high base (ISO 12800). Any ISO you dial in is produced by amplifying one of those bases.

The tool measures, in stops, how far your target ISO sits from each base:

stops from base = log2(target ISO / base ISO)

It then chooses the cleaner base. As a rule, the highest native base at or below your target is cleanest, because amplifying upward from a native base beats living between bases. Between the two bases the decision flips at the midpoint: below it the low base wins, above it the high base wins.

Switching base does not change the light reaching the sensor — ISO only amplifies the captured signal. So to keep the same image brightness when you move to the cleaner base, the tool reports the stop adjustment to make with shutter or aperture:

compensation stops = log2(target ISO / cleanest base ISO)

Worked example

On a Sony FX3 (native 640 / 12800) you want ISO 4000 for a dim interior. ISO 4000 is about 2.6 stops above the low base and about 1.7 stops below the high base — past the midpoint, so the high base (12800) is cleaner. Switching the camera to ISO 12800 makes the image 1.7 stops brighter, so to hold the same brightness you darken exposure by 1.7 stops: close the aperture or speed up the shutter accordingly.

Tips and notes

ISO values between the two bases are the noisiest — whenever you can, set exposure so your working ISO lands on or just above a native base.
The high base trades highlight headroom for shadow cleanliness, so in good light the low base still gives the widest dynamic range.
The listed camera bases are the manufacturer-published values; verify against your specific body and firmware, and use the Custom option for cameras not in the list.