CCD ISO?

[Mac]

Has anyone actually tried to work out the ISO rating of their CCD?
Might be an interesting challenge.

The maths is here.
http://en.wikipedia.org/wiki/Film_speed

could be a useful comparison for CCD V DSLR debates.

Mac

[MarkS]

I think ISO is a meaningless figure for comparing CCDs.

Whether using a DSLR or dedicated astro-CCD, the important figures are:
1) Gain (converts ADUs to electrons)
2) Read noise
3) Dark current
4) QE (quantum efficiency)

BTW, we've just measured Robert's Canon 450D read noise - it is twice that of the 350D i.e. about the same as the 300D.  But the dark current is less.  Very interesting ...

Mark

Later correction:  that first measurement was wrongly calculated - the 450D read noise is approx 4.2electrons at ISO 800 compared with 5.5 for the 350D. 

[Fay]

What does that mean, then Mark? The dark current bit

[MarkS]

Fay,

Thermal noise is caused by dark current.  Cameras are cooled to reduce it.

Come along to my talk (on noise) on Thursday to find out more!

Mark

[The Thing]

Thermal noise is the sound you make when your lager's too warm

Or you've no ice water for your Pastis

[Mac]

I think ISO is a meaningless figure for comparing CCDs.

Yes and No, every CCD device will have a base iso,

Its just that ones that are not in cameras dont have the option of turning on an amp gain to change the iso.

So the default of both my nikons which is 200, gives me a starting point.
yes it will have the set parameters, of
thermal nosie,
read noise
dark current ect

but i know that they are both iso 200.
and that their parameters are both different. due to being different sensors.
Neither of which change when I stick a lens on. or cool them down.
The other parameters will change but not their ISO

but my HX9 when i stick a lens on wont change any of those setting either.
Im just interested in what its iso is.

Just so that i can work out exposure times when i do stick a lens on.

Mac.