Note to self....
This is a photo of Lon Haldeman addressing the Oklahoma Bike Summit back in November. See the strong reflections in the shadows? Look carefully at the back of the gray shirt on the left and the black shirt of the guy in the center. This room was backlit by those curtains up front. Sunlight hit them and diffused through the room. This shot was one of the worst examples.
It disturbed me that the lens had this much internal reflection, but I didn't think it through until recently. I shot some neighbors Christmas decorations at night, and the reflection was so strong it appeared like a second set of lights! I tossed those shots away.
Light bounces around in a camera lens. Some passes through to the image sensor or film, but some small portion of it is reflected by all those glass surfaces. Most of them are coated to prevent this. That's the orange or blue stuff on the glass. Then it struck me - the UV filter I'm using isn't coated at all! In that test shot of a candle, a ghost image of the flames is hovering just above the top of the P.
Here's the same shot without the UV filter. Viola! No ghost image! Normally, I'd leave the filter in place because I can clean it with a handkerchief or even my t-shirt. I wouldn't do that to the front element of the lens. But I'll have to remember to remove the filter in those low-light situations or strong back light situations.
Learn from my mistakes!