Like most enthusiastic amateur astronomers I have a long list of gadgets and upgrades I'd like to acquire. But until I hit the lottery I have to prioritize these things. High on the list has been to replace my nearly ten years old planetary video camera. An ImagingSource DFK21AU042 color camera, it has served well and still can acquire good images of the brighter planets. But with a maximum frames per second (fps) of 60 (and 30 for dimmer Saturn), I feel the need for speed.
Based on what I've seen posting images to the ALPO gallery as well as some Internet research, I concluded that a ZWO camera would be a reasonable brand to go with. Another relatively easy decision was to get a color camera again. A monochrome, using R-B-G filters to create a final image, certainly offers better results, but it significantly increases the amount of time to acquire and process the files. And of course there is the several hundred dollars of investment in a filter wheel and those filters. I need to keep it a bit simpler, at least for now.
My other two primary criteria were a smaller pixel size and the ability to achieve a fps rate above 60. Fortunately ZWO does offer a nice comparison grid to see the differences among their many products. I finally settled on the ASI178MC with its 2.4µm pixel size (less than half the size in my existing camera) and potential fps greater than 100. I tried initially to order from distributors in the US but everyone was back-ordered, whereas ordering from ZWO directly I had my camera in about a week.
The first clear night (surprisingly I did not get the month of clouds curse that often accompanies new equipment purchases) I targeted Jupiter and Saturn with the Cyrus 10" reflector and the ASI178. FireCapture immediately recognized the camera, but I was stymied in getting the frame rate to exceed 60 fps, even with cropping the region of interest (ROI). But even so I was happy to see I could image Saturn at that rate which my old camera never achieved.
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| Saturn using the ASI178 |
A little more research provided some insight as to what might have been blocking the higher frame rates. The camera can run in either 14 bit or 11 bit color modes. The smaller color palette of the 11 bit allows a higher rate - but there was no way (that I could find at least) to specify the bit level using FireCapture. I downloaded the free ZWO interface, ASICap, and readied my laptop to use it the next clear evening.
The ASICap did the trick. As soon as I switched to 11 bit mode the frame rates could be boosted significantly, up to 150 fps on Jupiter with a tightly cropped ROI. With a faster speed there is a greater chance of catching more of those milliseconds long windows of stable seeing, hopefully leading to more sharp images in the sample. Of course seeing has a lot to do with the outcome regardless of fps, and so far I've not had a really good night of steady skies.
One unforeseen (but predictable) consequence of the higher frame rate is the much larger video file that is produced. Previously a 2 minute run on Jupiter yielded about a 2-3 GB AVI file, but now I am producing files that hit 7-9 GB in size. This then leads to a storage issue with no really great solution (at least not suitable economically). I will probably fill up my 2nd TB of online storage by October, so I will have to come up with a plan. Right now I am thinking of starting to rate the video captures in terms of quality and interest with an eye to discarding those below a certain rank (contrary to my planetary video hoarding tendency).
ASI178 at work
One
unexpected benefit with using the ASI178 is the much larger field one
can start at, making it much easier to find the target, center it, and
only then reduce your ROI to have it fill most of the frame.
In terms of the ASICap interface, while it is workable I still prefer FireCapture. For one thing I like having the ability to briefly pause the capture and nudge my target back into the field if it has drifted out. I also find the more prominent display of the metrics during capture (fps, elapsed time, file size) much easier than the small font at the bottom of the ASICap screen. I also like that everything of importance fits on the FireCapture screen whereas I find myself scrolling a good deal in ASICap.
Hopefully an evening with some steady seeing will present itself soon so that I can get a true sense of what the camera can achieve. In the meantime, as often happens when I have new equipment, I plan on spending some time searching CloudyNights and YouTube for tips and advice from my fellow planetary imagers.
