How can I use CHDK for a timelapse with gradual exposure changes or overexposure protection?
Asked 3/30/2011
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I’m using CHDK on a Canon PowerShot G12 to shoot a timelapse at fixed intervals. I want smoother exposure changes as light changes over time, and I’d also like a way to stop the script if highlights become severely overexposed to avoid damage.
My current script keeps the shutter half-pressed so focus/exposure stay fixed between shots. Is there a better approach for handling changing light during a timelapse in CHDK? Are there existing CHDK scripts or methods that can gradually adjust exposure, especially for sunrise/sunset, or monitor RAW/sensor data to react to overexposure?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
3
These problems were encountered when trying to compensate from the bright sunlight to the dark of night for sunset and sunrise events. There've been a couple of "sunset" scripts created long ago to circumvent these problems, as well as trying to adjust for exposures when the light levels are far too low and the camera's own exposure meter can no longer function. Done by polling the data directly from the RAW sensor data when needed.
Look into these scripts on these two links:
Originally by user4595. Source · Licensed CC BY-SA 4.0
user4595
15y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. This is a known CHDK timelapse problem, especially for sunrise/sunset transitions where light changes too much for fixed exposure.
The most useful next step is to use an existing CHDK “sunset”/auto-exposure timelapse script rather than starting from a fixed-exposure intervalometer. Community answers point to older CHDK scripts designed specifically to:
- gradually adapt exposure over many frames
- handle very low light when the normal meter stops being reliable
- poll RAW sensor data directly when needed
That makes them a better fit than holding shoot_half throughout the sequence, which keeps exposure locked and works against your goal of adapting smoothly to changing light.
For overexposure protection, the same CHDK approach applies: use scripts that evaluate sensor/RAW data and react when values exceed a threshold, including aborting or changing exposure behavior.
So the best path is to start from one of the existing CHDK sunrise/sunset scripts referenced in the community answers and modify that, rather than extending a fixed-exposure interval script.
Referenced resources in the answers:
- chdk.setepontos.com topic 2156
- chdk.setepontos.com topic 3079
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