Denny G wrote in post #5196730
Thanks FlyingPhotog. That's nice to know. I'll give it a try(the AF) but for me to tighten the zoom ring is out. I move around to much.
I use the 100-400 for air shows and have never needed an extender. I do like to keep the zoom ring fairly tight though, as otherwise you have to be very careful not to let it zoom whilst shooting. Even a fractional movement will cause a soft image and, if you have it too slack, you are likely to not be able to hold it exactly stationary, unless using quite fast shutter speeds. You will have to hold it steady if it is slack, as otherwise it will zoom out to 100mm every time you point it upwards (a bit problematic at an airshow).
It isn't a 'locked' or 'loose' choice, so I suspect by tightening the zoom drag flying photog meant tighten it to the point at which it won't slide on it's own, but will still slide when you choose to move it (although it may not be a very smooth action, due to the higher friction). That is what I do at airshows, although I may adjust the slack according to what I am shooting.
For example, if shooting a small aerobatic aircraft which will need 400mm all the time I will lock it tight. If shooting a formation team such as the Red Arrows, I loosen it off a touch more than usual as I will be rapidly changing focal length to keep the whole formation tight at various distances. I will never have it very loose however as that can degrade IQ with fractional fore/aft movements. I sometimes wonder if that is the cause of some of the complaints from people who say it is a 'soft' lens.