Hi
Admin has raised an interesting subject that may explain some of the reported UFO sightings on photographs.
A few years ago i took a photo of a fox in my garden through the bedroom window. The camera was a Canon EOS SLR and i was about 18 inches away from the glass. When the pictures arrived back after processing, the picture of the fox and garden were totally blurred, but i had a lovely sharp image of of a dirty window. I had inadvertantly left the camera on 'auto' focus. It had focussed on all the dust and dirt particles on the window.
If a lense is a bit dusty, some of the cheaper digital cameras that can only operate on auto focus will focus on the dust. Due to the dust being too near the auto focus sensors, they will appear out of focus and come up as blobs or orbs.
Better quality digital cameras give you the option of manual or auto focus and it may pay you to stick it on manual focus for certain pictures.
Even on manual focus, if the lense is dusty or has marks on it, these will be picked up (some times) even when the lense is set on infinity.
A dark sky at night will send the auto focus sensors 'hunting' as there is often nothing of substance for them to latch on to.
Always use manual focus set at infinity for night sky pictures.
Observer