Dark Signal
The Sony IMX183, like any other sensor, has dark signals that grow, in the absence of light, over time. There is an underlying dark current, like any sensor, and there are also glows. Whether they are true amplifier glow (unlikely, amplifiers are built into each pixel now, however there may be other heat-generating units on the sensor die), or due to heat or even other signal (IR?) generated by SoC (system on chip, the integration of all the necessary readout and image processing logic into a composite package paired directly with the sensor, something Sony does as a matter of course these days), I cannot say for sure. Regardless, the impact is the same, and the patterns and practices to manage it are the same as with any other camera that exhibits amp glow.
Dark Current
The true dark current for this sensor appears to be very low. The official rating is < 0.002e-/s @ -20C. With exposures up to 10 minutes long, I have had very few problems with dark current, the most notable exhibition of which is hot pixels. The hot pixel count of this sensor is very low, lower even than the Panasonic MN34230ALJ. In part, the MN34230ALJ also appears to have RTS (random telegraph signal) which leads to semi-hot pixels, pixels that appear hot but only for a short time before returning to normal, which limits the effectiveness of dark frames for correcting hot pixels. Only true hot pixels will be corrected by a dark, and in these terms the MN34230ALJ seems to dark current almost as low as the IMX183, at around -0.006e-/s @ -20C.
As temperatures rise, the IMX183 has better dark current characteristics than the MN34230ALJ. Where the MN34230ALJ seems to double fairly quickly, around every 4.5C or around there, the IMX183 seems to double closer to every 10C. Even as hot as 25C, dark current on the IMX183 is only 0.06e-/s, which is actually incredible. This is an area where Sony seems to do significantly better than anyone, managing dark current.
Amp Glow
Given that dark current is basically a non-issue with the IMX183, that means the main dark signal concern is amp glow. The glows on this sensor are definitely time-dependent, they grow brighter with longer exposures. The general characteristic of the glows seems to be about the same as with any other Sony CMOS sensor, which all (based on my testing of IMX178, IMX174, IMX294, and IMX183 sensors) seem to exhibit the same general pattern: A primary starburst from the right edge of the frame, two tighter radial glows to the lower left and right corners, and a very faint glow to the upper left corner. Under very deep integrations, some slight glow along the top and bottom edges, and a very faint bubble about half the height of the sensor at the middle left edge.
Below is a worst case example of the glows (1 hour of 900s dark frames), stretched to an extreme so that the full characteristic of the glow can be seen:
I say the above is a worst case scenario, because it really is. The strange thing about the amp glows here is they seem to grow faster with longer exposures. I tested this by integrating the same total integrated dark frame time, 1 hour, using a range of different exposures at unity (gain 111). Comparing 60x60s, 30x120s, 20x180s, 15x240s, 12x300s, 8x450s, 6x600s and 4x900s, a clear pattern emerges:
I am honestly not sure how to account for this, however it does indicate that stacking more shorter subs will result in less total amp glow than stacking fewer long subs. This lends itself better to LRGB imaging than NB imaging, as well as imaging at shorter focal lengths rather than long. LRGB galaxy imaging at 800mm should be quite ideal, with subs in the 2-3 minute range. That said, I have found that 10 minute narrow band subs at gain 53 seem to fair ok with amp glow, and the sky signal buries the glows enough that there is no readily observable increase in noise from them. This may warrant further testing of the glow growth rate at other gain settings to see if the behavior differs with gain.
In the area of amp glow aesthetics (), the Panasonic MN34230ALJ is the clear winner.
It's glows are far less intrusive, fainter, and don't seem to grow quite as much or the same way as the Sony glows do. If you are chasing faint details with narrow band, I think the MN34230ALJ based cameras like the QHY163 or ASI1600 are better options.
That looks a lot like the ASI 178. Before you reach that conclusion on the 1600 we need to see the QHY because my QHY178 cool amp glow is virtually nonexistent whereas the ASI has tons like the image above. The difference is the anti amp glow circuit which ZWO doesn’t have...
