I've been experimenting with low light photography. I've photographed something weird inside my camera and don't really know what it is. This is the image initially taken...
Seems inoccuious enough. After some processing though, I found the following...
What is it?
Some backgound. This was taken with a Nikon D80 set to ISO 3200 and a timed 30 sec exposure. Image format was RAW. There was a f2.8 - 4, 24 - 85mm zoom lens fitted (bulky - and I'll get to this later). The image was equalized and curve stretched by (a) GIMP. All images are /were RAW or PNG format so there shouldn't be any JPEG artifacts in there. So I have some questions.
What causes the white bit at the top of the image? It is not light bleed. The image was taken with the lens cap on, with the camera inside a steel filing cabinet drawer, in my unlit garage at night. It is not light bleed. Further, to confirm this I actually took 2 frames, turning the camera upside down onto its' view finder. This white bit is always towards the view finder.
What is the partial circle apparent in the bulk of the frame? Is this a thermal image? I believe that CMOS sensor based cameras can see a little into the near IR band. The lens is quite bulky and might have been warmer than the main camera body. Is the answer to question (1) also thermal. The top of the camera has a lot of controls and bits there.
What causes the vertical lines in the image? Is this something to do with the Bayer filter or the linear addressing of the individual CMOS photodetectors?
What causes the purple and green patches? I realise that these are not true colours, but nethertheless they are representative of macro scale intensity variations across the frame.