Hi all.  I thought I knew how to take long exposure photographs, but evidently I was wrong.  My previous experience was with a Canon 80D DSLR.  I've never tried it with a mirrorless camera.
I don't do it very much but went out a couple of times the last couple of weeks to brush up on it and had some weird results.
I currently shoot with a Sony A7RIII.  I was using a 10-stop ND filter mounted on a Tamron 17-28mm lens and wanted to use f/8 aperture.  I had my ISO set at 100.  I set the composition then put the filter on.
I was just playing around so I didn't have a particular exposure time in mind for the clouds I was using as my subject, I just wanted to do something like between 3 - 5 seconds.
I was in manual mode.  As I was adjusting my shutter speed I noticed that my aperture started to change.  I didn't think that was supposed to happen.  Clearly I don't know what I'm doing.
Was hoping you could recommend a good tutorial that would help me get back on track.
*Please note I also tried this with a Sony 70-300G OSS lens and had the same issues.

Any help would be appreciated.

Thanks!!!

Edited March 10, 20214 yr by D.R. Smith

Was Live View on? 
I seem to recall something about this happening, I can’t remember where I saw it... I’m wondering if it was a Mark Galer video