Setting up Bracketing function for sx40 in scripting? - Script Writing - CHDK Forum
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Setting up Bracketing function for sx40 in scripting?

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Offline redfordl22

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Setting up Bracketing function for sx40 in scripting?
« on: 20 / January / 2013, 11:24:41 »
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I already have CHDK installed on a 2gb SD card in my canon sx40 and would like to set up the bracketing feature for 5 exposures at -1,-2,0,+1,+2(5 exposures- 1ev apart)) for shooting in Raw for Hdr photography. My aperture setting would be at f8,iso 100 or 200 for night shooting)  How would i set this up under bracketing  and under scripting.  Can a Sdhc card be used to install chdk  and what size is best?
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Offline waterwingz

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #1 on: 20 / January / 2013, 11:27:49 »
Please don't post the same question in multiple threads.  The people who can help tend to watch all postings so you don't need to post the same thing twice.
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Offline pigeonhill

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #2 on: 20 / January / 2013, 11:49:17 »
Redfordl22

IMHO here are a few pointers for you:
* The SX40 sensor has a circle of confusion of about 6 microns (I think, please check);
* Based on this the hyperfocal distance at the widest aperture F2.7 and at the shortest focal length of 4.3 is going to be less than about 2m. Which should mean that you have a good depth of field from about 1m to infinity.
* My numbers account for aberrations, in other words, F8 is not the best way forward.
* Low ISO is a good strategy;
* lock off everything, ie manual focus mode and fixed WB etc.

Bottom line: try shooting at the widest you can on your camera and focus at the hyperfocal distance, ie you dont get the deepest dof by closing down apertures beyond the sweet spot, because of lens aberration. Try shooting at the widest and manually focus at the hyperfocal distance (llok on line for DOF calculators, or at Apps on your Android or iphone etc).

Cheers

Garry
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Offline msl

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #3 on: 20 / January / 2013, 12:06:59 »
Btw, CHDK has an inbuilt DOF calculator.  ;)

msl
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Offline pigeonhill

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #4 on: 20 / January / 2013, 12:17:03 »
But I don't think it accounts for lens aberrations, ie difraction. On a small sensor and CSC/PS camera, anything smaller than about F4.x moves you into the difraction limited zone.

I think the best strategy is to shot wide at the shortest FLs.

As I say, IMHO.

cheers

Garry
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Offline pigeonhill

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #5 on: 20 / January / 2013, 12:27:02 »
Maybe CHDK developers could add in the diffraction limited feature into the DOF calculator in CHDK?

It's only a few more calculations.

Just a thought.

Garry
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Offline lapser

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #6 on: 20 / January / 2013, 16:49:01 »
Quote from: redfordl22 on 20 / January / 2013, 11:24:41
I already have CHDK installed on a 2gb SD card in my canon sx40 and would like to set up the bracketing feature for 5 exposures at -1,-2,0,+1,+2(5 exposures- 1ev apart)) for shooting in Raw for Hdr photography. My aperture setting would be at f8,iso 100 or 200 for night shooting)  How would i set this up under bracketing  and under scripting.  Can a Sdhc card be used to install chdk  and what size is best?
You can install CHDK on large SDHC cards by formatting them first with FAT32. I have CHDK working with a 64GB card. Unfortunately, Windows built in format routine won't format larger SDHC card with FAT32, so you need to use a program. I've found this one works well:
http://www.ridgecrop.demon.co.uk/index.htm?fat32format.htm

You can set up "bracketing in continuous mode" to do what you want. You just need to let up the shutter after 5 shots. In alt mode, press <menu> and browse the menus for the exposure bracketing options.

I don't think there are any scripts that do bracketing in continuous mode, so scripts would go a little slower. Others may be able to point you to the best script to do this.

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Offline lapser

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #7 on: 20 / January / 2013, 16:51:33 »
Quote from: pigeonhill on 20 / January / 2013, 12:27:02
Maybe CHDK developers could add in the diffraction limited feature into the DOF calculator in CHDK?
I think he's asking about exposure bracketing here, not focus. But do you have a reference link describing the effect of diffraction on depth of field?
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Offline pigeonhill

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #8 on: 20 / January / 2013, 21:28:05 »
I personally use http://www.georgedouvos.com/douvos/TrueDoF-Pro_in_Action.html

Here is a site of fun reading http://www.normankoren.com/Tutorials/MTF6.html

BTW I am talking about exposure bracketing, as going much past F4 on a P&S camera takes you into difraction limited zone.
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Offline redfordl22

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Re: Setting up Bracketing function for sx40 in scripting?
« Reply #9 on: 21 / January / 2013, 11:10:44 »
lapser, yes you are correct  that i am asking about bracketing set up in chdk for sx40  and thanks for your answers to this query. I"ll see if i can set this up today.  Instead of holding down the shutter for continuous shots wouldn"t it be better to set up the remote cable release which chdk will allow you to do.  Holding down the shutter can lead to a little vibration.    If i have trouble setting up bracketing under the chdk main menu, I"ll get back to you.
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