SL2 DOF preview question

[dem331]

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A question regarding the DOF preview function. When I assign it to a button and press on the button a green F appears next to the F stop and I can see the DOF change as I stop down (SL AF lens). This is fine. 

When I press the button a second time a green s also lights up next to the shutter speed value. What is this for? It doesn’t seem to change anything.  
 

Thanks for the help. 
 

 

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[Jeff S]

Following FW updates, one can assign a custom button to toggle through three display options: no preview, preview with current aperture (depth of field), and preview with both aperture and shutter speed (exposure preview). 

[dem331]

Thanks. So I understand the exposure function is only  relevant for Manual operation, since with aperture priority exposure is changing as I change the aperture.