Started Jan 16, 2013 | Discussions thread
Mark H
Mark H Veteran Member • Posts: 3,612
'Extended' low ISO lowers clipping point...

Steen Bay wrote:

jimr wrote:

Steen Bay wrote:

Mark H wrote:

Steen Bay wrote:

jimr wrote:

On the back of the brochure the X20 Specifications lists the following:

"Sensitivity". AUTO (control available up to ISO 3200) Equivalent to ISO 100/200/250/320/400/500/640/800/1000/1250/1600/2000/2500/3200/4000/5000/6400/12800 (Standard Output Sensitivity)

ISO 125 and ISO 160 are missing, so think it's likely that ISO 100 is an extended ISO.

These particular ISO values are also missing on the X10 etc - so there is no difference in the specifications there.

The X10's missing ISO-125 and ISO-160 has puzzled me for some time.

Certainly, from my examination of the X10's RAW data at ISO-100, there is no evidence of the X10's ISO-100 being an 'extended' value.

Neither does 'DxO's testing find that either - for example, if the X10's ISO-100 was 'extended' then it's dynamic range measurement would be the same at ISO-100 as at ISO-200, but it is clearly better than ISO-200.

Yes, ISO 100 on the X10 is clearly a 'real' ISO. According to DxO the measured ISO at ISO 100/200 is ISO 124/232, so ISO 100 has almost 1 stop higher saturation capacity than ISO 200. Don't know why ISO 125/160 also are missing on the X10, but although the missing ISOs don't tell us anything in itself, then I still find it most likely that ISO 100 is an extended ISO on X20. Partly because it is on the other cameras with X-Trans sensors, and also because there isn't a single ISO 100 image in Fuji's X20 gallery.

so why would Fuji clearly label the Extended ISO on the X100S and then lie and Clearly and repeatedly NOT label it an Extended ISO on the X 20 ???

Maybe they just forgot to label it, we'll know soon enough. And it doesn't really matter, it's not a bad thing if ISO 100 turns out to be an extended ISO. It'll just mean that ISO 100 and 200 will have the same saturation capacity (can 'handle' the same amount of light/exposure without clipping),...

No, that's wrong.

The main consequence/cost of a so called 'extended' lower ISO is that you actually lose highlight range - because the sensor is getting a higher exposure, so it saturates at a lower point in that exposure.

...and it's quite likely that the X20 will have at least the same saturation capacity at ISO 100/200 as the X10 has at ISO 100. It's just a matter of how Fuji has chosen to calibrate the X20, a matter of how much highlight headroom the camera has above metered middle gray.

It's really impossible to say. There is no obvious reason for any particular sensor to have an inherently high, or low, 'base ISO'.

It's still better though, to have a low minimum ISO - for reasons such as lower noise (lower 'photon shot-noise') and better ability to cope with high light levels, and ability to use creative effects such as for example, wide aperture/DoF and motion blur without resorting to ND filters.

To that end, having ISO-200 as a lowest setting can be a problem - it's preferable to have a lower minimum like ISO-100 (or even lower).

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