Sony a6400 interval shooting bug?

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Original poster
Aug 6, 2021
Hello all, first post here but long time Sony a6000 series shooter :)
Since a year and a half i'm shooting with two sony a6400 camera's and with both I run into the same issue, which I will try to describe as concise but complete as possible in this thread.

I enjoy shooting day to night timelapses in which the light changes from a sunset into a rising milky way core during the night.
Obviously these timelapses last for an extensive amount of time, and so i'm plugging in a powerbank in the micro USB to power the camera while it's shooting.
This works great, as it still runs on the original battery but can last as long as there is power in the powerbank.
However, because this uses the micro USB port, there is no option for using an external intervalometer anymore, forcing you to use the built-in interval shooting function.
This shouldn't be a problem, as the app functions great (for the most part). Now the issue I discovered two months ago when shooting a timelapse of the milky way on Madeira island.

As the light changes a lot between golden hour and nighttime, I usually have my settings as follows:
Fast prime lens, F1.4 or F2.0
ISO auto between 100 - 3200
Max shutter ISO is set to 15 seconds, so only when the shutterspeed reaches 15 seconds, the ISO will increase to a maximum of 3200, untill that time it stays at 100.
This works great since the images stay noise free for as long as possible, while the camera is obviously on a tripod, so shutterspeeds are fine to increase until 15 seconds
when star trailing becomes notable.
The issue is that when using the interval shooting function, the ISO will never increase higher than 200, even when it's pitch black outside. I tried several times setting the
ISO on auto with the desired 100 - 3200 range, but on no occasion either of my a6400's increased the ISO to higher than 200.

The weird part is that when shooting single shots with the exact same settings, the ISO goes up nicely to 3200. But in the interval shooting it won't do it.
This caused an otherwise nice timelapse of the nightsky and sunset + sunrise to be ruined before I found out, all the frames where more than 5 stops underexposed.
Plugging in an external intervalometer could be a workaround, but since I need the USB port for power this is not an option.

Has anybody else experienced the same problem? I'm not sure if Sony is aware of this or where to contact them.
Curious to hear your opinions/experiences!


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