Tuesday, September 17, 2013

Atik power hunger

Atik 383L+ is for sure great bang for the buck camera - large KAF8300 sensor with over 8 million pixels, quite sensitive (about 55% peak QE and 45% for hydrogen alpha line) and no problems with software and hardware. Almost no problems...
One can find some reports in the Internet about excessive noise and hot pixels present in the raw frames taken with 383. Common factor for this phenomenon was low supply voltage. When the camera is supplied with voltage lower than rated the noise and hot pixels amount rises. When voltage drops to 11.5V or below the amount of noise becomes overwhelming. It may have effect only on cameras manufactured before year 2012. And I discovered it also affected my setup - in the picture below you can see fragment of the 15 minutes hydrogen alpha nebulosity region near by NGC6914 (the right part). The overall picture is just a noise :(

So far I was very happy with my 12V 5A power supply that feeds the whole setup. After taking the dark frames library with camera connected directly to power supply I also had not noticed any alarming noise. However after the camera first light I found out some more than unpleasant amount of hot pixels in the frames. I investigated Internet a little bit on it and decided to make some measurements. My 12V power supply gives voltage 11.9V that drops to 11.8V under full load. That's perfectly OK, because it means keeping rated voltage within 1.5% range - almost perfect. Not for Atik :) When taking darks the voltage applied directly to camera was 11.8V so the calibrations frames were in a good shape. However when camera has been attached to the setup the two additional connectors and about two meters of cable stood in the way. These obstacles gave another 0.5V voltage drop, so the effective voltage at camera was 11.3V - it was way too little and the hot pixels came out like mushrooms after the rain (like in the picture above). 

The supply voltage needed to be increased. There were several ways to do it - for camera alone, or the whole setup, with new regulated power supply, or some converter. I purchased a DC/DC step up converter to do some tests and to use it in the field. Now I am also able to connect it to the battery or akku and  have regulated 13.5V in the field to power up my set up. 

For the backyard astrophoto I use old but hale regulated power supplier 13.8V / 10A with decent transformer inside. It weights somewhere around 3kg and can be used for self defence as well :) It also heats like a little oven, but is extremely stable and simple to use and maintain. Under the full load (about 4A top) the output voltage from this supplier drops by about 0.02V. 

Only synthetic results so far, but promising :) My last calibration frames I took at 11.8V and the new ones has been exposed at 13.5V. The direct comparison is below:

Top row contains stacked master dark, bottom row single 10 minutes dark frames. Left pictures are at 11.8V, right ones at 13.5V. Even here the difference is obvious, and the pictures at 11.3V contains dozen times more hot pixels (see first picture in this blog entry).
Now I impatiently wait for clear skies...

As usual...
Even under the clear sky I already wait for another one... :)

Clear skies!

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