In the “good old days” all the digital cameras were using CCD (Charge Coupled Device) sensors and now almost all digital cameras use CMOS (Complementary Metal Oxide Semiconductor) sensors. CMOS image sensors are so much cheaper to manufacture and they behave better (more linear) in less than perfect conditions.
The way the sensor works (extremely simplified) is they receive the light from the photosite (a small lens that is front of the each pixel of the image sensor) and converts it to a signal.
The sensitivity is measured in ISO. There’s the base ISO and then as more electricity is pushed onto the sensor it becomes more sensitive to light, ISO 6400, &hellip, ISO 3,280,000 for the Nikon D5. The higher the electricity, the higher the sensitivity and the hotter the sensor gets. Which leads to hot pixels.
- For long exposure, you can use exposure stacking: a 60 second exposure can be done as 10 6 seconds exposures and stacking them in post will almost eliminate all the hot pixels.
- Many camera manufacturers, including Fuji have a Long Exposure Noise Reduction setting (usually, it kicks-in at 1 second and longer). The camera will take 2 exposures, both with the same aperture, ISO and shutter speed, but the second exposure doesn’t have the shutter open, then the CPU looks for hot pixels and map them out from the first exposure.
- Turn off the camera for a few minutes before taking the long exposure.
- Make sure that the camera is not in the sun or use a good shade before and during the long exposure. (Long exposure in the sun? Many people use 10 to 15 f/stops neutral density filters).
- Post processing: many software have a function to map hot pixels.
- Post processing: use the noise reduction of the post processing software to remove the red/hot pixels.
- Some people test their camera for hot pixels with lens-cap on. This test is the worst-case scenario and doesn’t represent real life.