Auto ISO question

[NHKeith]

Auto ISO is not doing what I expect so there must be something here that I don't understand. I am using it with settings default ISO 200, max 800, min shutter speed auto. With a 18-55 lens at 18mm, I am getting it using ISO 400 with a shutter speed of 1/6400 second. I don't understand why it isn't selecting ISO 200 when there is plenty of light. I am using aperture priority

Edited July 23, 2021 by NHKeith

[dward]

Check your dynamic range setting. If you have DR200 set, it will force your ISO up to 400 (creating space for the dynamic range process to work). Change your dynamic range setting to DR100 and see if auto ISO uses the lower ISO value. 

Hope that helps, 

David

[NHKeith]

15 hours ago, dward said:

Check your dynamic range setting. If you have DR200 set, it will force your ISO up to 400 (creating space for the dynamic range process to work). Change your dynamic range setting to DR100 and see if auto ISO uses the lower ISO value. 

Hope that helps, 

David

Thanks David - you are right! I had DR set to AUTO and changing it to 100 lets Auto ISO select 200.

That made me confused about what the DR setting is actually doing, The manual says to use higher values to reduce loss of detail in highlights and shadows. i.e. high values give greater dynamic range. Increasing ISO should reduce dynamic range so why would the DR option to increase dynamic range require high ISO? I found this description of what Fujifilm DR settings are doing: https://www.dpreview.com/articles/5426898916/ins-and-outs-of-iso-where-iso-gets-complex. What is surprising is this suggests that the greatest dynamic range comes from DR 400 and ISO 800. i.e. there is more dynamic range as ISO increases from 200 to 800.

Edited July 24, 2021 by NHKeith