At first I didn't know what you mean by "mirrored" but I now see that in fact the far right side of the image has somehow duplicated in reverse. I can only assume that when I created the composite I didn't do it correctly and the software did something weird. A simple crop will fix the problem.
This was shot with an old beat-up Nikkor 80-200 f4.5 AIS push pull lens and an 4T diopter. Manual focus, trial by error exposure on my D90. Biggest problem was waiting for any slight breeze. Heavy tripod and remote shutter release, mirror delay. Total investment in optics, around $70.00.