Hi TG,
Yeah, lot of dust ...
The CCD is in a closed enclosure, which is cooled down, and I need to get into a white room to clean it well and not get more dust inside...
The flat I posted is very very stretched to show what happens ...
I have a combination of optical vignetting and stray light through the filter drawer.
It took me some time to find that problem and fix it with an extra black protection around the imaging branch ... on going improvement.
Chhers
JY
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Airconvent
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hi jy
thanks for bothering to share your process with us....at least the newbies have an idea how you did it...so much work...I thought it was just a matter of point , expose, close shutter ..walla!
btw, can you care to elaborate on what this "flat" is all about? from the description it looks like you take the original shot, minus a dark noise shot and then enhance the resulting image..
rich
thanks for bothering to share your process with us....at least the newbies have an idea how you did it...so much work...I thought it was just a matter of point , expose, close shutter ..walla!
btw, can you care to elaborate on what this "flat" is all about? from the description it looks like you take the original shot, minus a dark noise shot and then enhance the resulting image..
rich
The Boldly Go Where No Meade Has Gone Before
Captain, RSS Enterprise NCC1701R
United Federation of the Planets
Captain, RSS Enterprise NCC1701R
United Federation of the Planets
Hi ,
As you can see in the original image, there is a lot of noise that needs to be removed.
- The electronic noise, generated by the CCD and electronics, it is directly related to the length of the exposure and the temperature of the CCD. For a 3 minutes image at zero degres Celcius, you take a 3 minute image with the shutter closed at zero degres, it is a Dark image.
When you substract it from the original image, you effectivelly remove this noise.
- The random noise, due to anything, electronic or visual. To remove it, you take several images and stack them. The signal is always the same on a pixel but the random noise differs. Stacking images increases the signal and decreases the noise.
- Dust on the objective, vignetting are taken care with a flat : you take an image of a white, even surface at the same focus as the astoimaging. The result should be an uniform white image but it is not, you get shadows from dust and vignetting (light in the center, darker around).
Dividing the astroimage by the flat, you remove those dust shadows and "flatten" the distribution of light.
This applies to any sort of astro-photos : for those who image with normal cameras and have not tried it yet, do it :
- Take a dark image : same duration as the image but in the dark with the shutter closed or the cover on.
- Take a flat image : image of a white wall, a fridge door, etc ... do not overexpose.
- Using some free software from the web (Iris comes to mind), apply the dark and flats, you'll see the quality improve a lot,
Cheers
Jean-Yves
As you can see in the original image, there is a lot of noise that needs to be removed.
- The electronic noise, generated by the CCD and electronics, it is directly related to the length of the exposure and the temperature of the CCD. For a 3 minutes image at zero degres Celcius, you take a 3 minute image with the shutter closed at zero degres, it is a Dark image.
When you substract it from the original image, you effectivelly remove this noise.
- The random noise, due to anything, electronic or visual. To remove it, you take several images and stack them. The signal is always the same on a pixel but the random noise differs. Stacking images increases the signal and decreases the noise.
- Dust on the objective, vignetting are taken care with a flat : you take an image of a white, even surface at the same focus as the astoimaging. The result should be an uniform white image but it is not, you get shadows from dust and vignetting (light in the center, darker around).
Dividing the astroimage by the flat, you remove those dust shadows and "flatten" the distribution of light.
This applies to any sort of astro-photos : for those who image with normal cameras and have not tried it yet, do it :
- Take a dark image : same duration as the image but in the dark with the shutter closed or the cover on.
- Take a flat image : image of a white wall, a fridge door, etc ... do not overexpose.
- Using some free software from the web (Iris comes to mind), apply the dark and flats, you'll see the quality improve a lot,
Cheers
Jean-Yves