Saturday, May 30, 2015

New ZWO ASI174MM Camera

Testing New Equipment

It was warm, even borderline hot on May 5th, but I withstood the heat because I was anxious to try my new ZWO ASI174MM monochrome camera. The camera is the small red cylindrical device attached at prime focus on the back of my telescope in the images below.
The new camera is theoretically superior to my old DMK41 camera in three ways. First, the chip size is significantly larger. The new ZWO camera's chip has 5.86 micron square pixels in a 1936 by 1216 array compared to the DMK's 4.65 micron square pixels in a 1280 by 960 array. This means the ZWO chip is 11.34 mm by 7.13 mm compared to the 5.95 mm by 4.46 mm DMK chip. The ZWO chip has three times the imaging area of the DMK chip. 

Second, the new camera has the ability to record a greater brightness range. The DMK camera is an 8 bit device capable of 256 brightness levels. The ZWO camera can function as an 8 bit, 10 bit, or 12 bit device. In 10 bit mode it records 1024 brightness levels. In 12 bit mode it records 4096 brightness levels. 

Third, the new camera has faster download speed. The ZWO camera uses USB 3.0 communication while the DMK uses USB 2.0. This speed increase might be the most useful improvement for my personal observing requirements. For reasons I've never been able to figure out the DMK camera usually freezes temporarily during capture downloads. For example, the capture of a 400-frame video takes 27 seconds when the DMK is behaving properly. But proper behavior seems to come and go at random. More times than not the DMK takes 54 seconds or more to download a 400-frame video. In 8 bit mode the ZWO took only 6.67 seconds to download a 400-frame video, and in 12 bit mode it took only 12.76 seconds! This is a very pleasant change from the DMK! Unfortunately, I still experience temporary download freezes with the new camera. The freezing isn't constant. It comes and goes as if the laptop is handling competing tasks. I just don't know what these competing tasks could be. It would be wonderful to discover some computer setting that would eliminate this problem.

The new camera's large chip size means a full disc solar image can be captured at prime focus with my Lunt 100 mm telescope. The picture below has not been cropped. It shows exactly how the full disc fits on the imaging surface. The field of view is 51.7 arc minutes wide by 32.5 arc minutes high. Resolution here is not pleasing, but the full disc image could be obtained from one video without making a mosaic. Unfortunately, illumination is slightly uneven from left to right, perhaps because the disc was not precisely centered horizontally on the chip.
I usually use a 2X Barlow lens with the DMK camera because it gives a more pleasing resolution than prime focus. So I used a 2X Barlow with the new ZWO camera to see how images would look. The following 3-image mosaic, made with the 2X Barlow, shows large sunspot group 2335 below center, 2338 near center, and newly visible sunspot 2339 near the limb in the upper left. (Click on the image for a larger view.) There is a slight uneven illumination, particularly in the bottom right corner. The resolution here is much better than the prime focus image, but still not quite as nice as what I get with the DMK plus 2X Barlow.
The next picture, a 2-image mosaic, shows filaments stretching across the southern hemisphere. It was processed to show disc features, so prominences are not visible.
The next image is the same mosaic as the previous one, but disc features are overexposed in order to reveal the filament to prominence transition on the right limb. (Click on the image to see the transition in more detail.)
The best picture obtained with the new camera so far is the following single image showing prominences, sunspot group 2335, and nearby filaments.
Resolution is not quite as good as I'd like. Click on the image to view it full size, then compare the area around sunspot 2335 with the resolution of the next image. You will probably agree that the DMK41 image below is a little nicer.
I may need to use a 3X Barlow with the ZWO camera in order to achieve the resolution I'm looking for. It will take a while to try different exposure times, Barlow lenses, and settings in the FireCapture software that runs the camera. But I'm encouraged by these initial results and I'm looking forward to using the new camera again soon.

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People say I'm crazy doing what I'm doing
Well they give me all kinds of warnings to save me from ruin
When I say that I'm o.k. well they look at me kind of strange
Surely you're not happy now you no longer play the game

People say I'm lazy dreaming my life away
Well they give me all kinds of advice designed to enlighten me
When I tell them that I'm doing fine watching shadows on the wall
Don't you miss the big time boy you're no longer on the ball

I'm just sitting here watching the wheels go round and round
I really love to watch them roll
No longer riding on the merry-go-round
I just had to let it go

John Lennon