In article <4n03gh$321@bfp.cc.purdue.edu>, bfp@bfp.cc.purdue.edu says...

>I recently photographed the moon (at night) and the print came back
>with two images on it. One was a sharp image of the moon and the
>other was a slightly larger, brighter, and blurry version of the
>moon. I took three of these pictures and in each case the moon and
>the blurry image were oriented such that the midpoint of the line
>connecting the two images was near the center of the print. [....]

Some lenses (particularly zooms) produce doubled images of bright
subjects against dark backgrounds, with or without a filter
attached. My Cosina 100-500mm f5.6-8 does it at several distinct
focal-lengths in its range - most annoying for night photography!
Hope This Helps