Av for 24h time-lapse with automatically calculated shutter speed above 1 sec - General Help and Assistance on using CHDK stable releases - CHDK Forum
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Av for 24h time-lapse with automatically calculated shutter speed above 1 sec

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Offline janis

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Av for 24h time-lapse with automatically calculated shutter speed above 1 sec
« on: 14 / August / 2010, 08:12:37 »
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Hello!

Spent Saturday morning to get CHDK working on G11 with 16GB card (windows). Great stuff!
I need to make time-lapse that could cover both day and night using aperture priority mode. And the problem is set limit to max shutter at 1 sec witch makes night photos too dark. CHDK overrides shutter speed enabling it to be manually set higher. Is it possible using CHDK to just allow Av mode to pick lower that 1. sec? Or is there some script that would calculate appropriate (and higher than 1 sec) shutter speed for set aperture?

Thank You!
Janis
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Offline reyalp

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Re: Av for 24h time-lapse with automatically calculated shutter speed above 1 sec
« Reply #1 on: 14 / August / 2010, 14:53:03 »
I don't know any way to change the built in AV mode limit. However, there are several "night" and "sunset" timelapse scripts in the scripting forum which may be useful to you.
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Offline fudgey

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Re: Av for 24h time-lapse with automatically calculated shutter speed above 1 sec
« Reply #2 on: 15 / August / 2010, 03:54:12 »
You can extend autoexposure Tv range by writing a script that first determines exposure at widest aperture, highest ISO and then uses APEX formulas to calculate Tv for your selected Av and ISO. Obviously the same applies to the short Tv range by going into half shoot with minimum aperture, lowest ISO. I believe you don't even need multiple half shoots as you will be setting Av, Tv, Sv as overrides during half press after autoexposure.

The simplest way to write the script is probably to require settin the camera to these incorrect Av/ISO setting before starting the script and giving the actual desired Av and ISO as script arguments.

But do note that there is a reason they limited autoexposure to 1 second. When it's too dark even for wide aperture & high ISO, the camera can't tell black from even more black as it just sees some noise. That's where the shot histogram method found in sunset timelapse scripts (they analyze the previous shot's RAW buffer instead of the noisy live view image autoexposure works with).
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Offline janis

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Re: Av for 24h time-lapse with automatically calculated shutter speed above 1 sec
« Reply #3 on: 15 / August / 2010, 06:34:36 »
Thank You very much! I did try out some scripts available here in forum and the results are just what I need.
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