From: "milton_aupperle" <milton@outcastsoft.com>

Date: August 31, 2009 1:50:40 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: Colour Jupiter from Ray


Hi Ray;


--- In Astro_IIDC@yahoogroups.com, Ray Byrne <ray@...> wrote:

My worry is  

that I'll saturate them and lose data I suppose, and I'm worried about  

noise (but I'm getting that anyway - probably just poor seeing).


As I indicated before, you can use the "Show Saturated" check box in the camera controls window (version 4.04.00 and up) to determine if your getting close to saturation visually. That way you get the correct brightness of the image and also make sure you don't saturate the pixels. Try setting the cutoff off value to 180 (70%) which should yield good results. It's also very useful when imaging the moon too, so that you don't wind up with over saturated crater rims or if your doing photometry measurements too, so that you don't saturate your stars.


With 8 bit cameras this becomes very important because you don't have a lot of latitude between pixel values like you do with 16 bit cameras.


On a noise related note, I was testing out the "Brightess" measuring code and decided to see how much variability one gets for 4 pixels (2x2 block) with different Gain/Brightness settings for a DMK 21AF04.AS camera.


Gain Avg Max Change

1023 5.1 23

0971 4.6 18

0900 3.2 14

0600 1.2 05

0300 0.7 03

0180 0.6 03


I was doing 1,500 measurements for each run, with max gain being 1023 and lowest 180. What it shows is how much variations of the pixels values are on average (5.1 out of 255 is +/- 2.1%) and the maximum value is the biggest change recorded between subsequent samples (23 out of 255 is 9.0% difference).


Once you cross over 600 gains, you start getting really big random changes in pixel brightness.


Each 2.4 pixel value change is a change of 0.01 magnitudes difference in brightness too. So you can see that unless you have your gains exceedingly low, you likely can't detect exoplanest with an 8 bit camera.


HTH..


Milton Aupperle