ADU setting

[swag72]

I hope that someone can help - I have read stuf on other threads about ADU figures and using them to ensure that you don't overexpose images.

I use a DSLR, capture the raw data and then stack in DSS. I know that people say that the information is in your capture software, well with raw files I use Canon's own DPP software - Can anyone help with perhaps either how I could determine ADU values using the software I have or point me in the direction of how I can do it.

Is there some downloadable software that I could use on raw in order to get the ADU values? I have searched the net so far with no success.

Hope someone can help. I've been told to use my capture software, but that's not helping me right now!

**I can get the RGB values for each pixel using the canon software - How can I then make that into an ADU figure? Is there a program I can do that with? Perhaps just put in the RGB values and it works out the ADU?

[Merlin66]

Sara,

Does the histogram function, which shows the peak and distribution for each colour give you same info?

With a DSLR the internal electronics are different from a CCD camera and the ADU may be "hidden" in the results.

A histogram which shows a smooth "top" - not flatened would infer that signal photons are still being counted....

HTH

[swag72]

Cheers Ken. I was wondering about keeping saturation in the stars and not blowing them out. I have a highlight alert on the software, which flashes at areas where I have 255,255,255. I suppose perhaps one way of judging exposure is to make sure I have none of these?

I can look at the histogram individually for each colour.

[FraserClarke]

**I can get the RGB values for each pixel using the canon software - How can I then make that into an ADU figure?

You already have They are the same thing. ADU is just 'how many counts are in this pixel', so for a DSLR it's the same as the RGB values.

[swag72]

You already have They are the same thing. ADU is just 'how many counts are in this pixel', so for a DSLR it's the same as the RGB values.

So when I look at the RGB figure what am I wanting? No highlights at 255,255,255? The brightest stars to have a figure all round at just below the 255 mark?

[FraserClarke]

So when I look at the RGB figure what am I wanting? No highlights at 255,255,255? The brightest stars to have a figure all round at just below the 255 mark?

Yeah, 255 means the sensor is 'saturated' -- it won't record any more flux in that pixel. However, you might want to accept that the cores of stars are going to be saturated if you also want to record faint structure in nebula -- the camera just won't have enough dynamic range to do both.

I think some people do short exposures to get an image without the stars saturated, and then use them to 'correct' longer exposures in post-processing. Details are beyond my knowledge though.

[swag72]

Thanks for that - Will work more on that basis then!