Ive pulled my hair out over several jugs of coffee trying to figure this out for myself and usually come to a dead end of confusion and despair. The Pilot pins on an optical printer (mine anyway) are on the right of the machine. But how then can you print 16mm to 16mm because after an 180 invert (the function of ALL lenses) the pins (now perfs) are on the wrong side of the film strip.

So, here is a visual sequence going through what is happening, and it seems ive been confused all this time because when you visualise a machine, you can can be on one of two different sides of it!!!

Look below, from left. You are looking at a 16mm (POS) film strip from the POV of the LAMP. This is how we lace a 16mm film into a projector.

Next you are looking at the same film strip from the LENS, or front of the projector. BUT not through the lens, just from the outside of the machine. We could also say from the SCREEN POV.

Next is how the film strip is mounted into printer gate, its basically an UPSIDE DOWN PROJECTOR. The work always travels UPWARDS in an optical printer.

Now, this image will do its 180 inversion and produce the next image, you are looking at it though from the PROJECTOR side, teeth on left! Imagine this another way. Imagine you put a small screen over the film gate. visible from outside, like projecting the image onto a surface. What will it look like. It will appear like the 4th image along, 180 inversion. Teeth on left……

BUT, we need to look at it from INSIDE the camera, from the equivalent of the LAMP, where we can see the SAME IMAGE as the first one, the PROJ GATE from LAMP SIDE and the teeth are now on the right, where they are mechanically. So the first and last images are the same. Inside the CAMERA is idenitical to a LAMP viewpoint.

We need to view the final image from the INSIDE of the camera, where effectively we are always printing TO, because its also the final PROJECTION view.