yes, Infinity Focus is possible with the Metabones ones. I currently own an Nikon-F to BMPCC (0,58x) and an Nikon-F one with 0,64x Magnification. Looking to also get an Standard 0,71x metabones one myself, because some DX Lenses Like the Sigma 18-35 and 50-100 Wont cover the Full 2.1 Sensor with the 0,71, cause Image Circle of the Lens is too small (Final Assembly has larger than DX-Format FOV!) and the 0,64x is anyways just barely covering the 2.1 Sensor, and has trouble with some Lenses. Both my Speedboosters have a Custom Made N1-Mount to also Mount on my Nikon1-Cameras and will mount to the Chronos with an Custom N1- to Chronos adapter. Given they are Mounted at the Correct Distance from the Sensor they allow for Infinity focus and a correct Focusing Scale on the Lens. They all Physically fit onto the Chronos Camera, but at least for the 0,58x and 0,64x, the Stainless Mount Of the Chronos needs to be Removed, not too sure about the 0,71x one, but could also need to be Removed.
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5G is quite a bit, considering the Probe Lens is also very long and the Sudden Start and Stop could have way higher G-Forces happening for just a very short moment. Depending on how Long You need the Pointy part of the Lens to be, i would try to support it as far in the Front as Possible. Most Sturdy Support would propably be to have some Kind of Round Clamping part in the Front around the Shaft of the Lens and then four arms to each mount on two of the M4 Threaded Holes On top, Bottom, Left and Right of the Camera Body, while the Mount of the Lens is attached to the four holes in the Front of the Body. If you make the Arms Beefy enough, i assume even a 3D-Printed Support would proppably do the Job just fine and be Sturdy enough, but please dont quote me on that, if it breaks. Savest bet would still be to have an Metal Adapter and Metal Supports, if you Wanted to be absolutely sure.