Excellent, thanks for all your help
What I did was I screwed the varifocal lens into the sensor housing straight after taking the old lens out as I was just thinking about trying to prevent dust.
I am waiting on a new mobius case to be delivered (current one is a bit tatty) so when it arrives I will unscrew the lens and put the new case back first before screwing the lens on
I don't know how old your original Mobius camera is but keep in mind that there was change to the housing at some point along the way such that certain vintage lens modules no longer fit the new slot. It's been so long I don't remember the exact point where the charge took place. In any event, if the new case slot doesn't fit your current lens module, now you'll know why.
Anyway, I realize I should have explained something that might have helped you better understand how to mount the new lens but better late than never as they say. You may find the explanation useful anyway.
Traditional M12 lens that are used in dash cams and actions cams are simple threaded barrels that screw into the module housing and are adjusted for focus by screwing them in or out until you achieve the proper focus.
Traditional camera lenses like on a DSLR or other standard still or cinema cameras have a fixed lens mount. Some are bayonet mounts and some are threaded. All these lenses attach to the mount in a very precise manor so that they achieve the proper distance to the film surface or senor plate and so that they are secure and stable. They can do this because they are designed with a "flange". The precise distance from the rear element of the lens to the sensor is called the "
flange focal distance".
These varifocal zoom lenses are designed for traditional larger CCTV cameras and so they have the flange. As such they were never really designed to attach to a tiny M12 lens pocket camera like the Mobius but they can.
By using the variable focus capability you can adjust the position of the rear element to compensate for what would otherwise be a
fixed distance on a traditional camera, although you might lose (or gain) some of the focal range of the lens. Thus you just screw it into the housing as far as it will go instead of having to screw it in and out to achieve focus. For this reason you want the case closed when you attach the varifocal lens to a Mobius.
No flange
Technically the mount on the camera is the actual "flange" and the flange focal distance
(FFD) is measured from there but the lens itself also has one that matches this same surface. Since the Mobius camera doesn't have an actual flange, for our purposes the back of the lens itself as shown above is considered the flange.
![cameraflange.jpg cameraflange.jpg](https://dashcamtalk.com/forum/data/attachments/54/54780-b377ad4e1c9837e9568ca593256c79c6.jpg?hash=s3etThyYN-)