Testing the Cooled ASI224
I’ve had a non cooled ASI224 since August and just recently received a cooled ASI224 that I have been testing for a little over a week. I find both cameras very challenging for DSO imaging. My primary interest is DSO imaging is for broadcasting on NSN (NightSkiesNetwork.com), not the typical AP imaging, but NLI (NearLiveImaging). Since I do NLI on NSN, my report will mainly reflect this avenue of imaging.
The ASI224 has been a real challenge, besides the USB3 driver challenge on a Mac using Parallels, it has also been a capture program challenge. The only two programs right now that can fully operate the cooled ASI224 is FireCapture 2.5 beta and SharpCap 2.7 beta with oaCapture currently only supporting the uncooled version. These are Solar System designed software that have been stretched to do long exposure DSO imaging. I won’t go into the issues I’ve come across using these programs with this camera, that’s not the purpose of this report.
The cooled and uncooled ASI224 has quite a bit of amp glow and requires Darks and they have to be done every time one uses the uncooled version but shouldn’t be required to be redone for the cooled version. Well I’m not finding this to be the case. The cooled camera’s temperature readout is read from the TEC and not the sensor so one has to wait a long time for the sensor to settle down even though the TEC temperature reaches it’s set limit quickly. So the darks taken in the beginning of the session may not be good at the end of the session. The TEC temperature regulation is very steady (I don’t know whether the sensor temp stays as steady) and the Peltier cooler will drawn down the temperature by 40+C. For an evening of imaging I set the temperature control to -30C and it stays there all night with no moisture accumulation issues. You do need a 12VDC power supply at a minimum of 2 Amps. The results of the cooling greatly reduces the warm pixels to almost zero as long as one doesn’t go much beyond a gain of 350 and uses realistic gain/exposure combinations. I typically used 15sec with a gain of 300 and for 60 sec a gain of 135 and for 180sec a gain of 0. I found that the amp glow is only slightly reduced.
My biggest issue with testing the camera has been with getting good Darks. Some nights they are good and some nights I just can’t seem to get them to work properly and if I do manage good Darks by the end of the evening they could change, even with cooling. Part of my Dark issue is how the programs I use implement them, but most of the issue I believe is with my lack of experience in this area. Like I’ve said I’m not an AP guy, I’m learning. The effects of Amp glow can take up to 30% of the image so it’s important to get the Darks right.
Having collected numerous images with the uncooled version I was looking for some major jump in performance. Well to be honest I was expecting to see very smooth images with minimal stacking, but haven’t really found it to be the case, yes it’s reduced but not dramatically, I maybe expecting too much. There is definitely a reduced amount of warm pixels when doing long exposures (60sec or greater). The cooling does, I’m told, help to reduce the dark current noise beside the warm pixels. When doing lucky imaging it doesn’t seem to mater whether the camera is cooled or not since the exposures are short and multiple stacks remove much of the noise. I prefer longer exposure times and will stick with 60sec and use 15sec or less for very bright objects. For my equipment setup I don’t need to do short exposures with many stacks.
I was hoping to be able to do single frame non stacked images for broadcast on NSN and hold the exposure times to under 180sec with minimal gain, except for clusters and very bright Planetary Nebula, it has not been possible. I have been using my C8 at f3 and my 80mm refractor at f3.7 fitted with an Idas LPS + IR filters. Something to take note of is that the cooled camera’s sensor sits deeper in the camera by 5mm and thus has a C mount back focus.
In conclusion, the cooled camera did provide more long term Darks and the longer exposure images were cleaner. I believe that in the hands of a more experienced imager more higher quality images can be generated than I have been able to produce.
I have collected images from the beginning in my ASI224 photo album, which is a combination of cooled and uncooled captures with the cooled ones placed at the beginning of the album and noted as such. The cooled camera images are all screen captures off my NSN broadcast screen with capture settings indicated. I did no post processing with the images unless noted.
https://www.flickr.com/photos/23705399@N04/albums/72157656927157919
