EOS-1D Mark III Unable to set ISO below 200

[harryset]

Canon 1D mark III, canon EF 24-105 IS, 1:4 L lens.  I am unable to lower the iso below 200 even with the CFN settings set  Max H, Min 100.

[Waddizzle]

Do you shoot RAW?  Which noise or image correction settings are enabled.  I think that one of the correction settings restricts the ISO range at the low end.

I shoot RAW and keep all correction settings disabled.

[deebatman316]

The OP most likely had “Highlight Tone Priority” enabled. When this is enabled the camera underexposes the shot by a stop. Therefore ISO 100 cannot be set.

[Waddizzle]

I don’t know if that older camera has that setting.  I have one, too.  It’s turned into a paperweight with an uncharged battery.

[deebatman316]

That camera has that setting so does my EOS 40D those cameras were both released in 2007. But a couple months apart. The EOS 40D was released in August of 2007. A lot features in the EOS-1D Mark III were in the EOS 40D. Such as the External Speedlite control menu.

[Peter]

It sounds like HTP, as already mentioned. There's no benefits to using that if you shoot raw.

[p4pictures]

There may be little benefit, but it does change how the image data is written to the RAW file. In effect the camera uses a different "curve" when digitising the data to convert the signal level to a stored value in the RAW file. Shooting the same scene in RAW with HTP on and off gives slightly different results. 

[Peter]

• ISO 100 in the metadata is changed to ISO 200
• The metering is changed to underexpose 1 stop
• The MakerNote tag Highlight Tone Priority is changed from 0 to 1 or 2
• The embedded JPEG will be brighter compared to the embedded JPEG at ISO 100.

For the raw file itself, I see no reason to shoot HTP.

ISO 100

HTP ISO 200

DPP4 reads the MakerNote tag Highlight Tone Priority and will add a different tone curve for 0, 1 or 2.

RawTherapee will try to copy the tone curve from the embedded JPEG, so we can actually see what is happening in the post processing.

ISO 100

HTP ISO 200