I'm seeing a splotch on my darks, and I'm not sure what's causing it. This is a modified T3i.
The darks are at ISO 1600, and 180 seconds.
I took my darks during the day, outdoors, under a covered patio, with the camera attached to the telescope and the (metallic) telescope cover on.
What's strange is the effect gets worse over the entire sequence.
I've attached a sample image from the middle of the sequence, and an image of the entire sequence, showing how the noise increases substantially over time.
Is this normal due to the camera body heating up from continuous image acquisition?