Measure linearity of sensor

[freiform]

Hi, 

due to lousy weather I thought about 'profiling' my cameras (Nikon and Canon DSLR, ASI120MM), i.e. in terms of noise as function of exposure time and ISO. This seems rather straight forward, but I also wanted to find the linear range of the sensors, i.e. ADU as function of exposure time. Maybe with ISO as parameter, although I do not know if this makes sense. 

How would I go about doing that? I thought of placing a small light source in a (relatively) dark room and increase exposure time, maybe defocus slightly to get a bigger area. The question is, how to measure the pixels values and over what area? Do I define a fixed size area around the defocused source? 

 Is there free software to to that? Can PixInsight do it?

Any hints would be appreciated!

Sven

[davew]

The easiest way I know of is here - http://oaltais.github.io/aplab/

Written by a member here called Altais.

If it works the way you want, let him know how you get on,

 

Dave.

[freiform]

Hi Dave, 

thanks for the hint, I already had my eyes on APLab. 

There still is the question of proper image acquisition and test signal, though.

Sven

[Astrofriend]

Hi Sven,

This was interesting, I also thinking about how to measure the sensors linearity in my Canon 6D. But how to get high quality data?

The cameras shutter doesn't have that precission I belive. Maybe have a LED and some strobe funktion to it, i.e. send one pulse, then 2 pulses, then 4 pulses and so on. That maybe will give higher precission than to use the cameras built in shutter.

 

I have recently installed the program AstroImageJ: http://www.astro.louisville.edu/software/astroimagej/, it has a function to linearize sensordata.

 

BR

/Lars