kylemcdonald

I got a reply directly from QHY indicating that the framerate of the QHY600 only increases with ROI, and not with binning. So unless the customer service rep is confused, that rules out their hardware. I am waiting for a reply from ZWO on their forum.

Thank you both for all your insight. I'm learning a lot 🙏 vlaiv, that image was not calibrated. When we initially recorded these I zoomed in on a sequence of a few consecutive frames and felt like the noise looked non-fixed, so I (naively) assumed that bias/dark calibration might not make a big difference. Also, watching videos at full resolution does not seem to reveal any strong fixed noise patterns. But at your prompting, I just read an article about the topic and I think I'm going to return to this. I still have the camera and recorder, so I will do some short cap-on recordings and build a dark and bias frame. Regarding the low read noise, I have also seen this same number from PhotonsToPhotos: 0.54e to 0.57e in the 102400 to 409600 ISO range. What's interesting to me about the equations you just shared is that somewhere around 2.3e input signal they converge at a SNR 1.1. Lower than that the a7S would have a slight advantage with the low read noise, higher than that the QHY600 has the advantage due to the QE. So this is really a head-to-head match. What's unclear to me is if the QE of the a7S accounts for the bayer filter or not. In other words, if we remove the bayer filter and shoot the same photons at an a7S II or III, will our QE measurement increase? Because if that is the case, and the QE without a bayer filter is closer to 80%, then that convergence point is instead around 11e. It sounds like my next steps are to keep pushing on the a7S somehow. Because we are operating with video in very low light, we are primarily in this read noise-constrained zone. If I can't get anywhere, then the QHY600 or ASI6200 both seem to be a good alternatives—assuming I can get the framerate up, and I can find one in stock It's just going to take a bit more programming and experimentation with the power. Thanks again for all the help 🙏

😱 This is incredibly helpful research. Thank you for this! It looks like the QHY600-Lite is the winner against the ASI6200, due to the slightly lower read noise, higher quantum efficiency, larger image buffer, and higher framerate. I'm not sure why the QE is higher or read noise is lower, I thought these were a properties of the sensor? And it looks like both have an SDK, which would allow me to use a low-power device like a Raspberry Pi or Jetson as an "HDMI converter": connect to the camera, buffer the images, process them on the GPU, and output over HDMI to an external recording device. This would all probably double our total wattage, which is currently around 25W (camera, gimbal, recorder). This will create a new bottleneck in terms of power requirements, but it would be worth it if the video is less noisy. Here's one thing I'm still not totally sure about. I've seen measurements of 0.54e- read noise for the highest gain settings on the a7S, but the QHY600 gives 1.1e- read noise at the highest gain setting in the high-gain mode. How can we compare the "overall sensitivity" in a way that accounts for this? Let's say we have 5 photons per photosite (or binned photosite), and ignore dark current. Can we say the following: a7S III SNR = (5 x 65%) / 0.54 = 6 and QHY600 SNR = (5 x 87%) / 1.1 = 3.9 Does this imply the overall SNR of the a7S III should be around 50% higher? Or have I oversimplified things? One way I can imagine that I may have oversimplified is that the QHY600 sensor may have a microlens array, while a debayered a7S III does not. This could make a big difference in photon count. Since it looks like the framerate concern is workable, do you have any intuition about this remaining SNR question? For some context, here is what a raw frame of video looks like from an a7S III (with bayer filter) at 4K f/0.95 1/25" (shot in high-gain mode), out on the ocean in good conditions (SQM-L was reading 21.4-22.2). (This was 2020-06-13 around Hawaiʻi looking towards the West, but I don't remember the exact time.)

Thanks again for your advice! We have been running at 24 fps with 1/25" exposure to maximize our light. The 1080p vs 4k distinction is important for the a7S II, but not the a7S III. The a7S II runs better at 1080p because it can do 2x2 pixel binning in hardware before it converts to 8-bit for HDMI. But the a7S III can output ProRes Raw at 4K 12-bit which allows us to either bin or not in post. The data is not a major issue, we record the ProRes Raw with a Ninja V to 2TB SSD drives. We are using a Zhongyi 50mm f/0.95 lens, which we found to be slightly sharper fully open compared to the similarly priced Zenitar 50mm f/0.95 (can't really go larger unless we plan a heist on the Carl Zeiss museum for one of their 50mm f/0.7 lenses). I have looked into the IMX455 sensor but it doesn't meet our framerate requirement (for example, only 10 fps for the QHY600). Our budget is limited to <$5000. I like your ASI294mm proposal, but I am concerned that a full frame sensor still has 3.5x more area than a 4/3" sensor, and also that it won't meet our framerate requirement (only 19fps at full resolution). Do you know if the ASI cameras have increased framerates when there is pixel binning, or is the framerate only a function of the ROI and ADC bit depth?

Thank you for the thoughts. I previously looked into these cameras and found that we were unlikely to get similar low light performance. But I would appreciate your feedback, I will outline my best understanding. Our requirements are: 24-30fps, 1080p-4k, around 50mm (40 degree horizontal angle of view), needs to be able to record continuously for more than 4 hours, and the lowest noise/most light we can get. This flash of light lingers for around 1/2 second and is sometimes reported as being slightly colored but often more dim than bioluminescence. Which would put it at around 0.01 lux, near the limit of mesopic vision. The a7S II and a7S III should be around 55-65% QE with a bayer filter (here is some evidence the a7S II has a better SNR than the a7S III). The camera you shared has 84% QE without a bayer filter. While removing the bayer filter should increase the amount of light we get in, it will also remove the microlens array, and total gains are still unknown. Maybe an extra half stop of light. The bigger difference is that a full-frame sensor has at least 6x the area of a 1" sensor. I'm unsure how to compare the read noise, which is reported 1.6e @ 30dB for the ASI183. I have seen read noise estimates for the a7S II around 1e in the higher ISOs (see here and here). So overall I think there should be no comparison, but mainly because of the sensor size. However, I am still new to all of this. If you think it's worth looking into I might just try to find an ASI183 dealer with a generous return policy, and try a side-by-side to check the noise characteristics. Thanks again.

Hello all, I’m helping with a cultural heritage project that requires an extremely low light video camera. We’re trying to capture a well-documented but never-photographed luminous phenomena that happens on the ocean at night. By following the posts on this forum and others, I learned about mono full-spectrum conversions. But my journey has been rough, and I wanted to ask for guidance from the experts I got lucky with my first debayered camera: I found a Sony a7S II on eBay that had already been modified by Monochrome Imaging. It worked great for a few months. Check out this test video I recorded showing glint from Jupiter on the Pacific, just off Venice Beach in Los Angeles. But two weeks before we set sail, the camera stopped working. It would go into a restart-loop when I turned it on. One repair center told me it was a problem with the sensor, but Monochrome Imaging offered to take a look (they have been amazing) under the suspicion that it was the main board. We just found out it is not the main board. Right after this glitch appeared, I contacted LDP LLC (MaxMax) in hopes of converting an a7S III to mono full-spectrum. LDP has also been amazing, they took the rush job, shot some beautiful test images, and shipped it to me. But when I unboxed and turned it on, the display briefly showed some blocky artifacts, and then only a black image. I was devastated. Now I am looking for another a7S III sensor in hopes that LDP can try conversion again, but I’m concerned that we don’t really know what caused the failure. So I’m here to ask: Does anyone have experience with successful a7S II or a7S III mono conversions? Where might I be able to find a reasonably priced a7S III sensor? The best I've found so far is $1600 on AliExpress. Is there anyone else besides Monochrome Imaging or LDP, preferably in the US, who have near 100% success rates? Or am I hoping for too much here? I know there are different processes (chemicals, scraping, laser) but I’ve had trouble figuring out who else is still operating. I also wanted to share some code I worked on as part of this project. I made a tool for extracting the raw 4K high-bit-depth pre-bayer-mixed image from an a7S III. If you stream from the a7S III to a device that can capture the ProRes Raw encoded video, like a Ninja V, it’s possible to get 4K grayscale video at 30fps.