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Automation of darks



I have an idea for a new feature in BackyardEOS, although it may actually be more appropriate to have a new application to do this.


Like many others, I am trying to build a dark library, so I don’t have to waste precious clear-sky time on generating darks.  Getting darks with the right temperatures is always a problem, so what I do is the following.


We’ll assume for the following that the best temperature to match between lights and darks is the internal camera temperature.  I realize this is not truly the “sensor temperature”, but please open another thread if you want to argue this point.  As far as I’m concerned, it’s the best temperature we have for matching.


Of course, we cannot directly control the camera temperature with DSLRs, but what I do is set a delay between my images that will result in darks of the desired temperature.  For example, the other night I took lights of 120 seconds at 800 ISO with an average camera temperature of 97F.  Ideally, to do the darks during the day I need somewhere where the ambient temperature is slightly above the ambient temperature when I took lights.


What I do is take a few darks (120 seconds, 800 ISO) to hopefully reach a steady-state condition.  At this point, I hope that the camera temperature is above the desired temperature, 97F.  I then take a few darks with a 30-second delay between shots.  I then adjust this delay time to achieve my desired 97F condition.  If the temperature is above 97F, I increase the delay, if it’s less, I decrease it.  This is why I need an ambient temperature above the lights’ ambient – I obviously can’t decrease the delay to less than zero.  I’m actually taking 97F darks as I write this, after following this process.  Once you get the proper delay locked in, it’s very easy to take as many darks as you want.


It strikes me that this process could be automated.  The application could automatically adjust the delay, just as I do.  In fact, you could even ask for a series of darks of varying durations, temperatures, and even ISOs, and it could all be automated.  This would be a huge help in generating dark libraries.  I’d be willing to pay for such an application, and I’m sure others would too.  For someone who is already familiar with how to control EOS cameras, it seems to me it would be pretty easy to develop.

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You might need to review your Logic:  

Most of us find that we need to provide Extra / External Cooling in order to Perform Darks Capture during the Day or Evening, as the Ambient Temperature is Higher than it was during the Middle of the Night when Lights were captured.  One cannot readily get the Sensor Temp to Drop by much simply by adding a Pause - even one of 30-60sec - as the Camera quickly becomes Heat Soaked and may require 15-30min to drop even a few Degrees toward Ambient.

In contrast, with a lower Ambient Temp one can work to Raise the Sensor Temp by performing several Exposures - even a series of Short Exposures - before one starts the "Production Run" of Darks.


In any case, there are a few Obstacles to any significant Programmatic Support to Managing Darks Collection:

In order to devise some Temperature Performance Curve, one would need a usable method to track Ambient Temperature - this is problemmatic as none of the previously supported Temperature Sensor Sticks are still in Production.

Neither the Canon nor Nikon SDK will provide the Current Sensor Temperature value in any way except to take an Exposure (although only a very short Exposure) - working to raise the Temperature to be monitored.

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First off, please don't tell me it can't be done.  I am doing it right now, albeit manually.  I am taking images with a 600-second delay between each 120-second image, and the camera temperature for each one is precisely 97F.  I can get as many images as I want at this temperature.  The long delay does not matter, since I can let it run all day and/or all cloudy night.  All that is needed is for the ambient temperature during the automation process to be slightly greater than that during the lights acquisition. This is not difficult when the outside temperature is relatively high.  The camera can be put inside a box or under a blanket (not a bad idea anyway for taking darks during the day).  When the outside temperature is low, you can put the camera outside or in a refrigerator or perhaps in an unheated building or garage.  Also, as the acquisition temperature drops, taking darks becomes less important anyway.


As I wrote, I am already doing this - I'm just suggesting that a simple application could be written to automate the process. 


I don't need to measure the camera temperature continuously (it would nice if I could, but it's not possible).  I just get the measurement when I take an acquisition.  I then adjust the delay.  I myself keep the "bad" images (those not at the desired temperature) as part of my dark library, but you could just throw them away.

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