Focus Problem with Tamron 70-180 and A7iii in low light...

Just came from an event in a high school auditorium which had a large brightly lit screen behind people whose faces you could barely see. I set the ISO at auto and their faces lit up nicely (ISO 20,000!) but with AF-S focus the lens hunted and hunted and wouldn't lock focus.

Additionally, as I have experienced on previous occasions, the camera would independently which to MF and in order to get it back to S-AF I had to shut it off.

It's looking like the 70-180 is not a good lens to use in similar situations and I will probably use the Olympus micro43 equipment with the 35-100 and the Panasonic 9mm,

I'm wondering what others have experienced with the 70-180 in low light and the camera switching from S-AF to MF by itself.

It is not unusual for AF to struggle in that kind of low light and MF is appropriate for low light photography. Having the camera switch automatically is not something I have experienced, though it is certainly called for in that situation. In my experience, the Tamron 70-180 is not particularly quick to autofocus anyway, much less in a low light situation.

Thank you for your observations, JC.

This was the first situation where I've used the 70-180 in such low light. I haven't really had a focus issue in brighter light.

The Sony and lens did rise to the occasion when there was a bright screen in a dark auditorium behind this speaker. With the help of DxO Photolab and Photoshop I was able to get a decent image at ISO 20,000.

Not entirely clear from your post: did you use the AF-S or AF-C focus mode?
The latter is much better and shows much less hunting.

I used AF-S.

It's been my experience that AF-C hunts more.

Yes, I agree AF-S coupled in my use with medium spot is better with this lens for stationary subjects.

Thanks for the confirmation.

Here is a link to some landscape/nature photos taken with the lens recently using an A7IV: www.flickr.com/photos/197970554@N04/albums/72177720307616453

Lovely set!

The lens gives me no problem in good light on my A7iii!

Thanks for sharing.

I wonder if this may help?

youtu.be/NSCXKblBccE

I found it the other day and switched the setting in Aperture Drive to Focus Priority. Don't know if it's helped because I didn't really have any issues with it.
I was hunting for "Aperture Drive" because I found it in the menu and had no idea what it was.... 🤣

Thank you for the suggestion.

Unfortunately, this setting is not available in the A7iii.

It only is available as an option if you using the shutter. If you are in silent mode, it is greyed out.