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Bracketing & RAW Questions - Help Please

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Offline firefly9000

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Bracketing & RAW Questions - Help Please
« on: 30 / May / 2013, 18:50:36 »
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I have a powershot sx40 hs. I have installed the sx40hs-100i-1.1.0-2806-full chdk.

My main problem before installing the kit was that Canon does not allow for bracketing WITHOUT changing the aperture. You can do it manually but that is a big pain. I'm trying to create HDRI maps so changes in aperture are a no-no.

I have a few questions please:

1. Is the any way with the chdk to make the camera take 3 bracketed shots without it automatically adjusting the aperture

2. I tried the RAW format which has more dynamic range but now my photos also have the vignette of the camera lens edges (you can actually get the whole sensor on the raw file and this shows the lens edges). Any way to reduce this to regular size. The problem with seeing the edges is that I can't stitch the photos and it's a pain to crop photo after photo...

Any help of pointing in the right direction would be much appreciated. Many thanks
« Last Edit: 30 / May / 2013, 18:55:46 by firefly9000 »
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Offline waterwingz

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Re: Bracketing & RAW Questions - Help Please
« Reply #1 on: 30 / May / 2013, 19:13:29 »
Quote from: firefly9000 on 30 / May / 2013, 18:50:36
Is the any way with the chdk to make the camera take 3 bracketed shots without it automatically adjusting the aperture
The little hdr scripts shipped with every CHDK package do exactly that.  Load either hdr.lua or hdr.bas (they do the same thing so just pick one) and run the script by pressing the shutter button while the camera is in <ALT> mode

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2. I tried the RAW format which has more dynamic range but now my photos also have the vignette of the camera lens edges (you can actually get the whole sensor on the raw file and this shows the lens edges). Any way to reduce this to regular size. The problem with seeing the edges is that I can't stitch the photos and it's a pain to crop photo after photo...
The whole point of using RAW is to get exactly what the sensor sees.  So there is no easy way to automatically crop it.   However, it would be fairly easy to do if you modify the CHDK source but then you would have an orphan custom version.

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Offline outslider

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Re: Bracketing & RAW Questions - Help Please
« Reply #2 on: 30 / May / 2013, 19:27:07 »
Moreover - you have maybe noticet, that on your RAW files you can observe barrel distortion. This is one of the reasons of vignetting - RAW covers more of the space of the scene than resulting jpg to allow the camera do some math and correct the disorition.

You don't need to correct photo after photo, there are some programs that allow batch photo processing, including cropping, resizing and even applying filters or other fancy things:)

On Linux I've been using program called convert that comes with ImageMagic package.
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