I suck at math and pull out the calculator for the simplest stuff so I wouldn’t even know how to begin calculating this. I’ve googled around but found nothing conclusive, I’ve asked chatGPT twice, which gave me two different answers, and I suspect they are both wrong.
Basically I want to know how to set the camera’s IBIS setting manually when using a 50mm lens with 46mm of extension tubes.
As far as I understand this, an extension tube decreases the minimum focussing distance and allows you to bring your camera closer to the subject. The focal length should not change by using an extension tube.
… how to set the camera’s IBIS setting manually …
What does the camera manual say about this?
The focal length doesn’t change when using extension tubes. But the IBIS setting might want a different measure, the distance between the lens and the sensor.
A 50mm lens focused at infinity is 50mm from the sensor. (I simplify the situation.) Adding a 46mm extension tube moves the lens out by 46mm, so the lens becomes 50+46=96mm from the sensor.
Perhaps that is the number to give to IBIS.
Not the question your asking but I found this site really useful when I was playing with extension tubes: Extension Tube Calculator