Testing the QSI 6120
I've been imaging with the QSI 6120 for almost 2 years now. Matt and I purchased one to use as a demo for our Seattle store, so I get to take it out in the field with customers quite often.
We decided to purchase this particular camera because we were anxious to get our hands on the new generation of low read noise Sony chips. The small pixels also yield a very reasonable 1.18 arc seconds per pixel when using our demo Tele Vue NP 101is, making it a nice match for our local seeing conditions.
Since it was a long, cloudy winter in Seattle and our thick blanket of clouds meant I couldn't be out under the stars as often as hoped, I thought it might be a good opportunity to test the camera with a flat panel and see just how it stacks up vs. the manufacturer specifications.
Testing was performed using the procedure outlined by Craig Stark in his wonderful Cloudy Nights post, Signal to Noise: Part 3 - Measuring your Camera.
These are the manufacturer's specifications for this chip:
High Gain (Specification): 0.13 e-/ADU
Full Well Capacity (Specification): 9000 e-
Total System Read Noise: <4 electrons RMS (typically <3.5 e- RMS, CCD specification limited) in High Quality mode
Dark Current: <0.002 electrons per second at -10°C
These are the results obtained from our bench testing. Note that the bench test was performed at -20°C, while the manufacturer's specifications were gathered at -10°C.
High Gain (Test): 0.14 e-/ADU
Full Well Capacity (Test): 9171 e-
Total System Read Noise (High Quality Mode): 2.3 e-
Dark Current: ~0.001 e-/sec at -20°C*
*Dark current is so low that it's very difficult to measure accurately.
So what does all of this mean in the field and qualitatively? The QSI 6120 has excellent sensitivity allowing you to gather light much more quickly; shorter exposure lengths will get you similar results as compared to other chips that have less quantum efficiency. Most notably as mentioned above, this has insanely low dark current noise. Like, it was tough to even measure it. Dark frames for calibration of images shouldn't be required if running the QSI 6120 at -20°C. This saves time by not needing to build up a dark frame library, and also saves time during the integration and processing steps.
The other spiffy design feature that leads to a different type of savings is that the QSI 6120 has a filter wheel built into the body of the camera unit. The filters are held much closer to the chip than having a camera and filter wheel be separate pieces. This leads to less vignetting while using smaller filters. The QSI 6120 can comfortably use 1.25" or 31mm filters, which are more cost effective options than the larger format filters.
The QSI 6120's electronics are also quite robust. In the two years of operation, there have been a few, shall we say, "sub-optimal electronic setups." The camera has been setup with wrong electrical polarity, over voltage, and under voltage, and it still operates with no issues at all. These sorts of errors can be known to fry the electronics on such sensitive devices, but the QSI 6120 is robust and rugged enough to handle these issues. Some of the images captured with this camera can be seen below: