Hot pixels

[Tweedledee]

I would be interested to learn about hot pixels.

 

These seem to be more of a problem in high gain, deep sky Mintron type video cameras rather than normal CCDs as far as I am aware.

 

I know they can be removed from the captured image using software, but are all hot pixels permanently faulty pixels in the chip, or are some temporary?

 

If temporary, do they usually appear in the same pixels intermittently, or just randomly around the chip?

 

Is there any method of use that can minimise or avoid hot pixels or a way to fix existing hot pixels?

 

Just trying to expand my very limited knowledge of the dark side .

 

Cheers,

Pete.

[dawson]

A brief article from the non-astro world on hot, dead and stuck pixels:

 

http://photographylife.com/dead-vs-stuck-vs-hot-pixels

 

James

[Perkil8r]

Hot pixels are generally in the same position on the chip for a period of time. They tend to occur when the chip gets hot, so keeping the camera cooler will help greatly. Most CCD's used for AP have cooling built in hence why the noise is lower. You can use calibration images (darks) to help get rid of them, they should be shot at the same temperature as the images you have captured with the same exposure settings / times and so on.

 

I say they tend to stay in the same position, because they do migrate a bit hence a set of darks can be used from one night to another, but should be replaced every few month. (or so I am told)

[dawson]

Mike, Surely an accurte dark has to be taken at the same time, ambient / sensor temperature, battery charge, pre-sensor cleaning, etc along with all the data subs, else these variables might not entice the hot pixels to show up on he night one is imaging.

James

[Perkil8r]

Mike, Surely an accurte dark has to be taken at the same time, ambient / sensor temperature, battery charge, pre-sensor cleaning, etc along with all the data subs, else these variables might not entice the hot pixels to show up on he night one is imaging.

James

 

In an ideal world yes, but I am not going to take a dark of 8 mins after each image of 8 mins otherwise you lose too much time. As long as the conditions are as close as is practical then you're okay. The rule of thumb is to use darks for upto 4 months, then replace them. Some folks do a "dark library" when the weather is poor. Personally I'm using darks close to the sub length and in some cases 8 months old. It's not too critical to be honest unless you are really at the very top of the game, which I most certainly am not.

[+Ibbo]

I have a few hots on the H9 they have increased over the years

 

what is all this talk of darks

 

 

with the ccd I do not use darks I use bias frames instead

 

DSLR yes I use darks but these can and do as Mike says last months

 

You can take darks when the cam has been removed from the scope

 

flats on the other hand need to be taken without moving position or focus

[Tweedledee]

Thanks everyone that is all very interesting. Got all the info I need there, cheers.

 

Well done finding that brilliant website article James, thanks.