Hi, all,
Yesterday, I was playing with a heavy lens
(560 grams, almost 20oz): a 200mm Soligor C/D
(which stands for “computer designed”!!!)
with Konica AR mount, adapter’d onto my X-T4.
Quite impossible for me to hold steady by hand.
I put it onto my tripods, used a cable release and shot a series
in my semi-dark playroom (i.e. long-ish exposures).
I still got motion blur :-(((((((((((((((((
Remedy: I changed shutter from mechanical to electronic.
Sigh.
Have fun!
Claes in Lund, Sweden
Quite often, these older and larger lenses have their own tripod mount built in — in many cases, they’re much heavier than the camera, so it balances the weight more evenly and helps prevent the lens tipping forward (which will cause motion blur in long exposures).
Yeah, I have a Nikkor 200-500 that I mainly use for wildlife photography. It is a nice lens, but it weights about 2.5Kg.
It has optical stabilisation, but it is still difficult to hold steady. I either use a monopod screwed into the built-in tripod mount, or occasionally a gimbal head on my tripod.
Have you tried standing sideways with the target to your left, supporting the lens on your left shoulder and looking into the viewfinder with your left eye?
@EspE1 I got motion blur even with the camera/lens on a tripod and using a cable release.
Note: on long exposures, that is. Seems as if the mechanical shutter was to blame,
since it helped switching to electronic shutter. 
If the exposure is of the order of a second, the vibration induced by the mechanical shutter can produce blurring in any camera (I suppose it’s worse the longer the focal length). My camera (Canon 5D mkII) has a “pre-open mechanical shutter option” specifically for that, which is basically your electronic shutter for the first curtain.
This is counter-intuitive because to me a heavy lens has more inertia, thereby resisting the tendency to change spatial positions as rapidly as if the camera were laden with a mere pancake lens… it does take some muscle tone to hold the camera steady by itself; I suppose if you are not physically trained for it, the untrained triceps will continuously fight the untrained biceps & pretty badly blur a handheld 1/250" shot at telephoto length.
When I had the D850 with the Tamron 70-200 f2.8, using the included lens collar and a shutter speed slower than the focual length always gave me a blurry photo. The included lens collar was plastic. $40 later I had a 3rd party lens collar and things got way better.
Now the Z 100-400mm has a metal collar, and that is excellent.