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!

Saturday, September 14, 2013

To catch a cosmic ray

Cosmic rays are very high energy particles that penetrate Earth atmosphere and sometimes even reach the surface. High energy means much, much higher than for example we are able to generate in the Large Hadron Collider. Most energetic cosmic rays particles observerd had energy 40 million times larger than particles accelerated in the LHC. These particles are mainly originated outside the Solar System and even outside the Milky Way. Every few moments at least one of this particles goes through your body. They have sufficient energy to alter the state of electronics integrated circuits causing errors to occur such as corrupted data in memory or incorrect performance of CPU.
They also affect day by day astronomers work of course causing different artifacts on long exposured CCD sensors. Here is the dark calibration frame taken with Atik 383L with exposition time of 20 minutes. The sensor has not been actually exposed to any light - it was tightly covered with the metal cap. You can see (when enlarge) there some hot pixels and some thermal noise (sensor has been cooled to -20C). And also during these 20 minutes some cosmic rays hit the sensor surface at different angles and caused some artifacts.

In the next picture some of this artifacts have been cut out and enlarged. You can see how different they are. You can also try to imagine what happened during this exposition, when those cosmic wanderers eventually hit the sensor surface after the million years of traveling across the space...

The origin of cosmic rays is still a little bit mysteriuos. It is believed that some of them are created during supernovae and other big stars explosions, but active galactic nuclei probably also produce cosmic rays.

Clear skies! (even under cloudy sky cosmic ray can hit you :) )

Monday, September 9, 2013

Floating in the hydrogen sea II

About a month ago I wrote a blog entry with NGC6914 nebula floating in the hydrogen see - http://astrojolo.blogspot.com/2013/08/floating-in-hydrogen-see.html . And I just wanted to make the same frame using the new Atik camera just to compare between Atik and Canon. Here is the result:

Quite nice, but the Atik victory is not so obvious. Of course I still need to learn a lot about developing and processing monochrome images made through LRGB filters but the Canon also do his job well (of course modded Canon). Here is the direct comparison:

Clear skies!

Saturday, September 7, 2013

Wood solid

Setting up the components to start the night session took me about half an hour every night. That's why eventually I decided to build up a pier at my backyard. It is fnished with wood panels, but of course contains much more solid core - concrete and steel.
The base has been made as concrete plate 80x80cm large placed 80cm underground. The base has been made of concrete and 6mm diameter steel rods. Then pier itself has been made as concrete cylinder 20cm diameter with steel rods inside. After some preliminary stability tests (see pictures below) everything has been burried with soil. 
Power supply cable has been carried from the home to the pier under ground. Below you can see some pictures from the construction site.

Clear skies!

Wednesday, September 4, 2013

Atik is here

DSLR has been eventually replaced with dedicated astro camera - Atik 383L+. This one is equipped with monochrome Kodak sensor KAF-8300 with 5.4um pixel size and 8 Mpx resolution. The sensor is cooled by TEC to the temperature 40C lower than ambient. Comparing to the Atik 314L I previously had for some time the sensitivity seems to be similar, however 383 camera seems to be a little bit more noisy. Also noise is not so uniform as in 314L camera and it is harder to process it. KAF8300 sensor also has more hot pixels, however after cooling it to -20C everything looks quite ok :) The main difference is the pixel number - Atik 383 has over four times more pixels than 314L. In my opinion it is the best bang for the buck these days - there is no cheaper astro camera in the market with 8Mpx resolution.
The new setup is not completed yet - I still wait for OAG and coma corrector adapter, but the night was so sweet that I decided to take first light :) Camera was attached to the filter wheel only (standard filter set: LRGB, Hα, Oiii, Sii) and no coma corrector, so the only center part of the frame was usable. Guided with finder and QHY5 and cooled to -20C.

First of all first lights - the M57 Ring Nebula in Hα - single 10 minutes exposure. Nice ring, test passed :)

Next one is Abell 2197 galaxy cluster - contains about 300 galaxies and is over 400 million light years away. This one is 8x5 minutes luminance only. Galaxies as faint as 19.5mag have been recorded.

And then during the same night some narrowband imaging - M27 Dumbbell planetary nebula. I managed to collect 5x10 minutes for Hα and Oiii fitlers. So, M27 in hydrogen alpha line: 

and in the oxygen line:

and my first bicolor astropicture:

I must say the camera meets expectations - causes no problems during installation and work. If you look for high resolution and affordable astro camera I may recommend this one to you. Atik 383L+ is available both as monochrome camera and one shot color RGB camera.

Clear skies!