Why is minimum native ISO 200 on many mirrorless cameras?

Because there isn't much gain in DR and noise from going lower perhaps? The occasional user who finds it inconveniently fast could use an ND filter.

We spent decades wanting faster film. I recall Kodachrome II at 25ASA (=ISO), with pretty much the fastest slide film as High Speed Ektachrome at 160. Kodachrome 200 was a liberation for many.

So no tangible gains from lower base ISO would be my suggestion.

a_c_skinner said:

Because there isn't much gain in DR and noise from going lower perhaps? The occasional user who finds it inconveniently fast could use an ND filter.

We spent decades wanting faster film. I recall Kodachrome II at 25ASA (=ISO), with pretty much the fastest slide film as High Speed Ektachrome at 160. Kodachrome 200 was a liberation for many.

So no tangible gains from lower base ISO would be my suggestion.

Click to expand...

There would be tangible gains, such as not needing an ND filter as often.

Using fill flash on a sunny day is easier at ISO 100 than it is at ISO 200 due to easier to sync flash, which would be especially beneficial to Fuji camera, which have a rather slow max shutter flash sync speed of 1/180.

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 ??

baobob said:

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 ??

Click to expand...

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?

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)

I think it is due to how ISO is measured ….. Fuji tend to underexpose by 2/3 stop, so ISO 160 on a Fuji is equivalent to ISO 100 on a Canon … Nikon used to measure the same was as Fuji (and base ISO was 200), but then changed and base ISOs went to 100 or even 50 …. I’m sure someone will confirm …. Or explain better!

It's because of the way companies measure ISO. Fuji and Olympus use the Standard Output Sensitivity method while Canon, Nikon and Sony use the Recommended Exposure Index.

io_bg said:

It's because of the way companies measure ISO. Fuji and Olympus use the Standard Output Sensitivity method while Canon, Nikon and Sony use the Recommended Exposure Index.

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Yup, that's it.

To the OP - Here is a lengthy explanation if you're interested: https://www.dpreview.com/forums/post/64387801

io_bg said:

It's because of the way companies measure ISO. Fuji and Olympus use the Standard Output Sensitivity method while Canon, Nikon and Sony use the Recommended Exposure Index.

Click to expand...

And just to head off at the pass any temptation to use io_bg's comment as a springboard for another "Fuji's ISO measurements are 'cheating'" thread, be sure to read Brian Kimball's contributions in the comments under the following post:

notchy said:

io_bg said:

It's because of the way companies measure ISO. Fuji and Olympus use the Standard Output Sensitivity method while Canon, Nikon and Sony use the Recommended Exposure Index.

Click to expand...

And just to head off at the pass any temptation to use io_bg's comment as a springboard for another "Fuji's ISO measurements are 'cheating'" thread, be sure to read Brian Kimball's contributions in the comments under the following post:

https://www.dpreview.com/forums/post/64815229

Click to expand...

Actually, my first instinct was to say: Oh, so Fuji and Oly are doing it right, and the others are actually doing it wrong.

(But I guess that there is no right or wrong, just different ways to measure something, and the only thing right is when you've got the right exposure).

notchy said:

io_bg said:

It's because of the way companies measure ISO. Fuji and Olympus use the Standard Output Sensitivity method while Canon, Nikon and Sony use the Recommended Exposure Index.

Click to expand...

And just to head off at the pass any temptation to use io_bg's comment as a springboard for another "Fuji's ISO measurements are 'cheating'" thread, be sure to read Brian Kimball's contributions in the comments under the following post:

https://www.dpreview.com/forums/post/64815229

Click to expand...

Thanks so much for pointing out excellent threads that already possess this information and spirited conversations about why and why not for Fuji and base ISO.

To the OP, the search function in this and any other forum is your friend. Starting with a solid search before posting a question will give you the proper background and will probably change what you want to know from a posting….or not. I always start out with a strong amount of searching a topic prior to posting (if I can’t find exactly what I’m looking for). Good luck and happy shooting!

Yes, of course, but like a lot of things people talk about on here modest gain in fairly specialised circumstances.

Bigger Fujis go up to 1/250th and have a low range for ISO too which gives you 100ISO in effect.

Just saying

Some cameras give you a staggering range of ISO values, for example, the Sigma fp.

From Sigma's specs.

ISO Sensitivity (Recommended exposure value) Base ISO

[Still]
ISO 100,640
[Cine]
CinemaDNG 12 bit / HDMI RAW:ISO 100, 3200
MOV / CinemaDNG 10 bit, 8 bit, HDMI 4:2:2 8 bit:ISO 100, 640

Settable Range

ISO 100-25600 / Expanded sensitivity ISO 6, 12, 25, 50, 51200, 102400

..............

I'd be happy with ISO 25 on a Fujifilm body but ISO 6 would be amazing, but using it requires taking multiple frames.

Here's a link to the first of a two-part article written by DPR's Richard Butler on ISO: https://m.dpreview.com/articles/9698391814/the-ins-and-outs-of-iso-what-is-iso

Part 2 is linked at the end and includes a good discussion of Fuji's DR modes.

A few posts in this thread attribute the reason that many Fuji X-series cameras have a base ISO of 200 to Fuji's use of Standard Output Sensitivity (SOS) versus other manufacturers use of Recommended Exposure Index (REI) as the ISO definition used. I'm not persuaded this is the sole or even the primary reason. I say this because, though I've done a bit of looking, I'm unable to find an informed article or post on the topic that provides a foundation for the underlying assumption that SOS requires a base ISO of 200 while REI allows a base ISO of 100.

In any event, Fuji camera users do have the option to use f-stop, shutter speed, artificial light sources, light modifiers, and filters to manage exposure and make photos with good detail, definition, pleasing lightness, and minimal noise.

--
Bill Ferris Photography
Flagstaff, AZ
http://www.billferris.photoshelter.com

The X-T20 sensor will blow your older cameras away in terms of both noise and dynamic range. Don’t worry about it.

Fuji underexposes every image by a little bit, and raises the tone curve to compensate. This results in more recoverable highlights, but loses an equivalent amount of shadow noise.

But this means the resulting picture is a little bit lighter than the hardware ISO number it is taken at. To go with the standard brightness nomenclature (comparable to other manufacturers), the published ISO number is increased.

TL;DR Base ISO on Fuji is ISO 100, but underexposed and with a raised tone curve. Which results in a brightness that is most similar to ISO 200. The latter is written to the raw file.

A step up from 25 or 64 in my Kodachrome days.

Tim van der Leeuw said:

baobob said:

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 ??

Click to expand...

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

Click to expand...

Exactly!

Tim van der Leeuw said:

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?

Click to expand...

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).

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?

Tim van der Leeuw said:

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)

Click to expand...

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.

Edited in Later: Some current Nikon DSLR have native ISO starting at 100 ISO, and Sony mirrorless at 50 ISO. That's native ISO.

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