IQ180 long exposures

[cunim]

Been trying some black field exposures (lens cap on). Has anyone else seen the corners brighten as a function of exposure time? At 10 sec I am getting values of 17-30 in the corners and zero elsewhere. Happens on the DF and on tech bodies. I assume the camera is doing its dark field thing so this is puzzling. Attached image has contrast boosted for visibility.

 

[mvirtue]

That is heat noise from the sensor.

 

[Jack]

Why not shoot a real picture and see how the corners look? Taking a black-frame then having the internal black-frame subtraction is probably what's accentuating it.