Imaging with the QHY 183C
I’ve been imaging with the QHY 183c camera for the past 6 months or so (or at least as much as possible given the Seattle Fall and Winter seasons). After a rather steep learning curve on controlling the settings on this camera, I have since fallen in love with this chip and am looking forward to using the monochrome version.
There are many advantages to this camera. One of the most immediately noticeable on the stat line is the size of the pixels: an astoundingly small 2.4 microns! There are many assets provided from this aspect alone. One is that this allows excellent sampling on widefield imaging rigs. With the average seeing conditions here in the Pacific Northwest, we generally aim to sample at 1 arc-second per pixel. This camera hits that perfect sweet spot at a modest 495mm focal length.
I’ve been imaging at 400mm focal length which still provides a respectable 1.24 arc-second per pixel sampling rate. I’ve never felt like I was undersampling my data, nor had a reason to drizzle my images. There are many telescope options that pair exceptionally well with this camera in that “short, fast refractor” style.
The other advantage of this chip that goes hand in hand with it’s pixel size is the total pixel count present on the camera. The 183C provides a whopping 20 mega-pixels. You’d be very hard-pressed to find a dedicated astrophotography camera with that sheer quantity at any price point, with this resolution usually reserved for full-frame or larger cameras. Imaging (and printing) with 20 mega-pixels is quickly addicting, and I hesitate to move to any camera that doesn't have at least this pixel count.
This leads into the last advantage of having such small pixels: even with huge resolution, the chip itself is squeezed into a 16mm diagonal. This means that there is less worry about vignetting in fast systems, and for the monochrome version, smaller filters are needed, thus saving cost.
The tiny pixel size would normally have a downside associated with it: it would take longer to gather your light with smaller pixels (see the blog series, Astrophotography Pixel by Pixel for further discussion of this aspect). While that is still the case and cannot be avoided, what the 183 chip does provide is Back-Illuminated technology. This swaps the traditional order of the photo receptive and the electronic components of the chip. The end payoff is that the camera boasts 84% quantum efficiency.
84%. I’m going to let that value sink in a bit.
With all of the advantages to this camera, I encountered some operational difficulties. There was some fine-tuning required in order to maximize the potential of this camera. The original version of the camera that I tested suffered from significant amp glow on the right side of all my frames. So much so that when first starting out, I would regularly need to crop off about 30% of each frame when shooting for 300 seconds. Furthermore, the amp-glow did not calibrate out as expected. This turned out to be a user error (PEBKAC). Once the gain and offset settings were dialed in correctly, the amp glow was significantly reduced, and easily controlled with calibration frames.
What I gleaned from QHY and other user experiences, the ideal settings to reduce amp glow are:
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QHY has since updated this camera including a glow suppression function to help minimize the glow effect. I’d be surprised to see any amp glow remain after these steps, though if for some reason it is not removed through batch-pre-processing in PixInsight, it can be controlled with the inclusion of flat-dark calibration frames and manual pre-processing.
This small finesse to the settings unleashes an absolutely fantastic astro-imaging camera.
The camera I have been using does not have the amp-glow suppression function. All of the 183 cameras from QHY now include this function and when paired with the settings above should entirely remove any amp-glow concerns.
All in all I have been incredibly impressed with the QHY 183C. Once the amp glow challenge was under control, I've been addicted to this camera. It’s a great fit for wide-field imaging systems, and I for one cannot wait to get hold of the monochrome version.
Some sample images from this camera are below after the statistic and information pictures. I hope to have many more data sets with this camera in the future!
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