Problem with long exposure in S95

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Problem with long exposure in S95
« on: 28 / May / 2014, 14:35:50 »
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Hi all,

I have a Canon S95 that I'm using for astrophotography. Without CHDK take pictures of 15 "exposure in manual mode without problems.
But using the CHDK (stable and beta - branch k). Within 15 seconds using the same parameters and aperture, ISO, etc, a violet glow appears in the upper left.
The "solution" is to configure CHDK to subtract the dark pixel, but for astrophotography draw my own darks, I need the raw image without any processing.
As I said, this happens to me with both the latest stable version and the beta. But it strikes me that without the CHDK not have that problem.

If someone can give me a help will be grateful.

p / d: sorry for my bad English.

Ivan

Re: Problem with long exposure in S95
« Reply #1 on: 28 / May / 2014, 15:49:24 »
Without CHDK loaded or running,  the Canon firmware is doing a dark frame subtraction for you - and thus modifying the image.

As you've noticed,  you can turn that off using CHDK and get the true image. Which includes the "blue glow" - search "amp glow" for more information.   What you probably want to do is take a reference dark frame ( lens covered ) every 30 frames (approximately) and use post processing software in your PC to remove the glow.

This script might be of interest :  http://chdk.wikia.com/wiki/Meteor_Intervalometer_with_Dark_Frame_Management
« Last Edit: 28 / May / 2014, 17:56:31 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

Re: Problem with long exposure in S95
« Reply #2 on: 28 / May / 2014, 19:05:18 »
Thank you very much for the clarification!
 
One more query please. The RAW file generated by the CHDK is equal to that generated by the camera firmware? So far I'm using the generated firmware.

Greetings and thanks for the script, it is useful to me!

Re: Problem with long exposure in S95
« Reply #3 on: 28 / May / 2014, 19:24:29 »
One more query please. The RAW file generated by the CHDK is equal to that generated by the camera firmware? So far I'm using the generated firmware.
CHDK RAW&DNG are an exact copy of the camera's sensor image data.

Canon RAW may include corrections for lens effects on the image like distortion, clipping/vigneting - especially at wide angle lens settings.

You need to decide which works best for your application.
Ported :   A1200    SD940   G10    Powershot N    G16


Re: Problem with long exposure in S95
« Reply #4 on: 28 / May / 2014, 19:50:04 »
Thanks for your reply.!

I'll try to capture some night pictures in both formats and then see the result.

Again, thank you very much!

*

Offline reyalp

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Re: Problem with long exposure in S95
« Reply #5 on: 28 / May / 2014, 23:06:30 »
Canon RAW may include corrections for lens effects on the image like distortion, clipping/vigneting - especially at wide angle lens settings.
I would expect that the data is essentially the same, and the difference is software that understands Canon raw format can apply the corrections automatically.

Other differences:
Canon RAW is likely to be faster.
Canon RAW is compressed, so it takes a bit less space.
CHDK raw may be available in some modes where Canon raw isn't.
Don't forget what the H stands for.

Re: Problem with long exposure in S95
« Reply #6 on: 29 / May / 2014, 08:22:45 »
Canon RAW is compressed, so it takes a bit less space.

This difference in size RAW files prompted my question about the difference between the two formats.
If the weather permits, I will use the telescope tonight and bring out some pictures in both formats and then stacking and process see if the result changes.
Then tell them if there is a difference.

Thank you very much!

 

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