Why is minimum native ISO 200 on many mirrorless cameras?

Started 2 months ago | Questions thread
OP Charley123 Senior Member • Posts: 1,054
Re: Why is minimum native ISO 200 on many mirrorless cameras?

Erik Baumgartner wrote:

Charley123 wrote:

Tim van der Leeuw wrote:

baobob wrote:

The X trans IV sensor BSI allows ISO 160 as base.

This ISO "restriction" is it due to a defavorable SNR at low ISO due to very small pixels ??

I don't know, Canon APS-C cameras have equally small pixels but are sold with a base-ISO of 100!


However the Canon cameras do not have a "low" ISO setting and Fuji cameras do. In fact, the X-T20 sensor should have a low ISO setting of ISO100 -- I assume that the camera will also let you select an "L" setting for ISO?

Yes, the X-T20 has a ISO 100 setting, but that's a pull ISO, not part of base/native ISO.

Pull ISO (on any camera) reduces dynamic range and tends to cause highlights to blow out. Pull ISO is not ideal. It's just a method of last resort when you really need ISO 100 (like when using fill flash on a sunny day, or wanting shallow DOF on a sunny day).

ISO 100 on your X-T20 will reduce available highlight headroom, but does not limit DR. It basically equals ISO 200 + 1 stop of exposure compensation ...if you don’t clip any highlights (not typically a problem in low to medium DR situations), you can indeed make better use of the available DR and improve the noise in the shadows by a stop vs. shooting at ISO 200.

Bright sunny days are when I need ISO 100 (typically for fill flash situations). Unfortuneately bright sunny days are usually when there are high dynamic range scenes. So what to do?

Or, you can just shoot at ISO 200 and up the exposure compensation when the situation allows it ...which is what most people would do.
It has been my experience that with Multi metering, the Fujis don’t tend to overexpose much at all and will often require a -1/3 compensation at ISO 200 with a sunny high DR midday scene to avoid clipping anything important in the RAW file. The other metering modes DO tend to underexpose quite a bit - sometimes by a stop or more.

For using fill flash on a sunny day, or when wanting to use a large aperture (low F number) on lens for shallow DOF on a sunny day, ISO 100 is often needed. It would be ideal if it were native/base ISO 100 so that full dynamic range (to keep full dynamic range). Having to use pull ISO 100 reduces dynamic range and is therefore not ideal.

Since Canon and Nikon DSLR have native 100 ISO, why don't mirrorless cameras like Fuji and Olympus? Are there any mirrorless cameras that have native 100 ISO? If not, why?

That's what my X-H1 has at least and that's the same sensor.

So perhaps the real base ISO of a Canon APS-C would also be ISO200, but Canon chose for marketing reasons to start with ISO 100 as base instead of calling that "low" ISO??

I have been wondering myself for a while though, what is the real meaning of base ISO and what is the value of a low ISO setting that Nikon and Fuji cameras have? Why not just call that low ISO the base ISO, what's different about it?

(Perhaps it's called "low" ISO because it is achieved by negative gain instead of positive gain? Which would mean it's an artificial lower ISO because it doesn't actually give you extra DR)

Canon Rebel T2i stated specs say base ISO is 100-6400. Independent reviewers have tested it and confirmed that 100 ISO is native. They verified by comparing performance at 100 ISO to 200 ISO.

The Rebel T2i is a 14 years old DSLR enthusiast camera that includes native ISO 100. Canon Pro cameras from that time have native ISO 160. Same with Canon and Nikon 14 years ago. So why are mirrorless cameras in 2021 struggling to get native ISO below 200? Even the latest Fuji only offer 160 ISO.

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