Interesting, and thank you.
It obviously varies from person to person, some people are more stable / don't move as much as others, obviously.
Personally I managed to get very sharp shots with a Canon 100-400 L IS Mk I at 400 mm and 1/40 s, mounted on APS-C, no problem, repeatable.
However, I have to agree with Klaus. When it comes to IBIS, I think Oly is still the one to beat currently, despite its in-built magnification factor. Half a second is generally not a problem for me with a stabilized lens and body.
Kind regards, Wim
P.S.: Before I forget, in most instances the cut-off point for effective IBIS is considered the slowest shutter speed where you have at least 50% of images sharp. So, 70% at 1/20 at 5 m is actually quite good. It means more than 3 stops effective IS considering you are using it on an APS-C camera. For landscapes that appears to be around 1/40s based on what you report, so about 2 stops gained. The 100 mm is in comparison to FF effectively a 150 mm lens, so you'd need at least 1/150s for a sharp shot based on the general rule of thumb for sharp pictures. This is the basis of my calculation here.
It obviously varies from person to person, some people are more stable / don't move as much as others, obviously.
Personally I managed to get very sharp shots with a Canon 100-400 L IS Mk I at 400 mm and 1/40 s, mounted on APS-C, no problem, repeatable.
However, I have to agree with Klaus. When it comes to IBIS, I think Oly is still the one to beat currently, despite its in-built magnification factor. Half a second is generally not a problem for me with a stabilized lens and body.
Kind regards, Wim
P.S.: Before I forget, in most instances the cut-off point for effective IBIS is considered the slowest shutter speed where you have at least 50% of images sharp. So, 70% at 1/20 at 5 m is actually quite good. It means more than 3 stops effective IS considering you are using it on an APS-C camera. For landscapes that appears to be around 1/40s based on what you report, so about 2 stops gained. The 100 mm is in comparison to FF effectively a 150 mm lens, so you'd need at least 1/150s for a sharp shot based on the general rule of thumb for sharp pictures. This is the basis of my calculation here.
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....