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Dark frame acquisition - capture based on sensor temp



Hi Guylain,


I hope you are well. 


Can you read the sensor temperature at any time you wish?  Really I'm asking about reading the temp. while in a paused state, not directly after capture.


Here's why I ask:  I'm envisioning a way to make capturing temperature matched darks easier.  I do all my dark frames at some date after a night of captures, so I know the target temperature for my sensor.  Currently i try to have the camera in an environment that matches the outdoor light frame temp. as closely as reasonable.  But I still have to build a pause into the plan to allow sensor cool down.  This is likely due to the lack of breeze and perhaps the camera on a covered porch so it can't radiate heat to the night sky etc.  So I have to play with the pause length and so forth to get a good batch of temperature matched darks.  I have to monitor the process until I get it working well each time.


What if I could capture dark frames based on sensor temperature?  Set up the number of frames, ISO, exp length etc., and a target sensor temperature.  If the sensor is too cold keep capturing frames with no pause.  If the sensor never heats up to the target temp so be it, the process isn't successful.  More often I think the sensor will become hotter than the target temperature (if the camera environment is rational) requiring a pause for cool down.  Poll the sensor temp and when it gets to the target temperature trigger the next dark frame.  This amounts to a variable pause length based on temperature.  The temp rise during a capture should be fairly consistent for a given starting temp., hopefully yielding a nice set of darks with some throwaway frames from the beginning of the process.


Let's face it I'm getting spoiled and lazy.  I'd like to set up a plan and go to bed, finding a nice set of temp matched darks in the morning.  I've tried to avoid too much checking and automation in the description (thereby allowing failure if the sensor never gets hot enough for example).  You already provided the extended delay time which has helped with waiting for the nighttime temps to drop low enough.  The idea above could make a mundane task easier if implementation isn't too insane.


Thanks for taking the time to consider this one.


As always Best Regards,



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Most all DSLRs, especially the Canon's, only expose the Sensor Temp data as a field embedded in the EXIF Data of a Completed Image.  So, a complete Exposure including the Download to the PC is required in order to "Poll" the Sensor Temp.


If you assume that you'd start with the Camera and Ambient Temps being Lower than the Target Temp, then continuous Exposures simply to sample the Sensor Temp EXIF data would work into your scheme.


The biggest concern with your suggested Workflow would be the Excessive Number of Shutter Activations that could occur, especially if the Late Night Ambient Temps make it difficult for your Camera to reach the Temps necessary to Start recording a batch of Darks...


Do realize that you aren't Limited to shooting your Darks at Night!!  Since the Camera is Capped Off, Darks can be Shot in the Daytime - any time that you have the Inclination to put in the Effort...

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Hi - thanks for the reply.  I was afraid the data might only be available via EXIF, so that kind of negates the whole idea.  Your point about excessive shutter counts is valid for sure.  For this to be reasonable you'd want to start out well with the camera environment appropriate.  I didn't want to get too carried away with the programming to handle failure modes.



I do capture darks whenever it's convenient.  An environmental chamber would make this less hit or miss, but that's an effort in itself and not necessarily worth it.  I'm almost done with a whole ton of dark captures from my recent vacation, and it wasn't all that bad really.  My mind just starts to ponder when baby sitting dark captures, plus I'm getting lazier with age.


Thanks again,




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An environmental chamber would make this less hit or miss, but that's an effort in itself and not necessarily worth it.


Interestingly, an "Environmental Chamber" is what I recommend to most All who ask about Darks.


Now, my recommended "Environmental Chamber" is a small-to-medium sized Picnic Cooler - with a couple of Plastic "Blue Ice" blocks included in order to drop the "Ambient" Temp to your desired Target (about the same Ambient as that of the Night when you Imaged your Lights).  Simply connect up the Laptop, run the USB (and maybe Battery Replacement) Cord in through the Cooler Lid, set the Laptop atop or aside the Cooler, and start your Darks collection.


Myself, because of the SE Arizona Desert Heat, use the same "Environmental Chamber" in order to Cool the Camera before Imaging Use on those Nights where it doesn't drop much below 100*F until at least Midnight...

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Yup - I've done the cooler and ice blocks + fans (sometimes) too when the weather doesn't cooperate.  It doesn't stay as hot here in the Southeast as you describe thank goodness!  The chamber I'd like to build would have a TE element to heat or cool and a temp controller.  Maybe I should finish all my other projects first!






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Well we're going off topic but my experience is you really need a "cold finger" to get heat out of the camera. With out it I was only able to cool into the low 50's (F) but with a cold finger can get to 35 degrees (with ice as heat sink). 

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