I am still quite new to Blender. I have tried searching the official Blender manual and watched several YouTube tutorials and searched for various related strings on the WWW but I haven't found anything to answer this question.
I have set up a camera rig using a couple of empty objects, one on a path and another on another path which is local to my point of interest. I have used constraints to control the camera view and the movement of the camera and target empty objects.
My problem is this - I want to lock the roll (rotation about the camera's local Z axis).
I understand that for every day stuff that the camera should try to stay "upright" but in my situation I am flying around an object in "space" where there is no up/down thing.
There are times during the animation where the camera wants to suddenly roll and much to fast. This is generally when the local Z axis of the camera reaches a vertical aspect.
I have gone into the graph editor to try and at least tame the rolling action and that works to a degree.
Ideally I would like to either have more control over camera roll or lock it altogether. I have tried locking various elements but nothing seems to want to stop camera roll.
I will add a GIF showing how the camera rotates as it goes almost vertical:-
I have since rendered a video and uploaded to YouTube. I will post a link to the time just before the camera begins to roll.
Okay, I have been doing some more research into my perceived problem here.
I created a new simple project with just a cube, a camera and a path (Bezier).
It seems to me that having set the camera up with the Follow Path constraint, linked to the path, and then the Track To constraint, liked to the cube, we are no longer able to rotate the camera at all as it appears to be locked. It is fixed such that the camera's Y axis is always as vertical as possible. And this is understandable, while setting up scenes which are Earth bound and we do not want a camera view which is suddenly upside down.
But then I watched one of the official Blender tutorials with regards to tracking constraints:-
As I am new to Blender and having watched so many tutorials up to this point none of them mentioned the Damped Track constraint. When I tried to use this constraint instead of the Track To constraint I noticed that we are now able to changed the camera's rotation.
I still need to play with this some more. I tried it quickly just now in my current project and there was still some undesirable camera roll, but I am guessing that because the camera can now be rotated I should be able to add keyframes at points where I want to control that rotation in order to counteract the roll.
Time for bed now... I will report back once I have spent some more time on this.
cheers, and thank you for your patience.