What are the key distinctions between ZWO’s latest planetary cameras, namely the ASI662MC and the ASI678MC? The ASI678MC provides a superior resolution, a higher frame rate (FPS), and reduced read noise at an additional cost of $50. On the other hand, the ASI662MC offers a higher quantum efficiency (QE) and an increased Full Well Capacity. Both cameras employ a 12-bit Analog to Digital Converter that can be adjusted to 10-bit (RAW16 & RAW8) to enhance the frame rate. Compared to older models, the new ZWO cameras incorporate cutting-edge Sony IMX sensors with STARVIS 2 technology, resulting in zero amp glow. They also feature a special HGC mode to minimize read noise and preserve dynamic range when using higher gain settings.
In the past decade, ZWO has introduced a total of ten “uncooled” color cameras that are primarily designed for planetary, lunar, and solar imaging. Among the latest additions to ZWO’s camera lineup are the ASI662MC and ASI678MC, both released in July 2022. Positioned within the mid-range price segment, the ASI662MC is available at $249, while the ASI678MC is slightly higher at $299. Let’s explore a detailed comparison regarding these two newer mid-range planetary color cameras, comparing their features with each other and also with the older models that have been on the market. If you’re new to planetary cameras, I recommend reading this blog post where I explain important features to look for in a planetary camera. For those interested in reading my initial tests of the ASI678MC including some first pictures, click here.
Resolution
The initial distinctions between these two cameras revolve around resolution and pixel size. The ASI678MC boasts a resolution of 3840×2160 pixels with 2 pixels per micron, while the ASI662MC offers 1920×1080 pixels with 2.9 pixels per micron. If we were to pair either of these cameras with a 2000mm focal length telescope, such as a Celestron C8, it becomes evident that the ASI678MC provides a broader field of view at 0.20 arcseconds per pixel, whereas the ASI662MC offers 0.29 arcseconds per pixel. For optimal planetary imaging in favorable seeing conditions, a pixel size of approximately 0.25 arcseconds per pixel is generally recommended. It is worth noting that both cameras are capable of encompassing all the planets within their respective fields of view, even when utilizing a 2x Barlow lens to extend the focal length to an impressive 4000mm, as illustrated in the accompanying image.
When comparing the resolution of the two cameras for Moon and Solar Imaging, the ASI678MC would be able to capture the entire disc of the Moon or Sun within the frame when used with a telescope having a focal length of 450mm. In contrast, the ASI662MC would require a telescope with a slightly shorter focal length of approximately 300mm to achieve the same result.
Frames per second
The reported maximum FPS on vendor websites for both cameras can be misleading, as the cameras have different resolutions. However, upon closer examination of the manuals and comparing both cameras at a similar resolution of 1920×1080 pixels with a 12-bit (RAW16) depth, the ASI678MC is specified to achieve 95 FPS, while the ASI662MC is reported to reach 76 FPS. Since planets are relatively small objects, reducing the resolution to 640×480 pixels at 12 bits yields 215 FPS for the ASI678MC and 161 FPS for the ASI662MC. Consequently, the ASI678MC offers a faster frame rate when used at a comparable resolution. It is important to note, though, that the quality and length of the USB 3.0 cable as well as the capturing device used can impact the maximum FPS attainable in real-life scenarios.
Read noise and quantum efficiency
Both the ASI678MC and ASI662MC cameras feature the newer built-in HCG (High Conversion Gain) mode, which effectively reduces read noise at higher gain settings. In the case of the ASI678MC, the HCG mode automatically initiates at a gain level of 182, while for the ASI662MC, it starts at 252. Consequently, the ASI678MC achieves a minimum read noise beyond those gain levels of 0.6e-, whereas the ASI662MC achieves a minimum read noise of 0.8e-. In terms of Quantum Efficiency (QE), the ASI678MC exhibits a slightly lower QE peak of 83% compared to the ASI662MC, which peaks at 91%. Notably, the green and red wavelengths of the ASI662MC demonstrate a peak approximately 10% higher compared to the ASI678MC.
ADC and Full Well Capacity
Both the ASI662MC and ASI678MC cameras support both 12-bit (RAW16) Analog to Digital Converters (ADC) which can be reduced to 10-bit (RAW8). Due to the larger pixel size of the ASI662MC, it boasts a higher full well capacity of 38.2K compared to the ASI678MC, which has a full well capacity of 11.3K.
ASI678MC and ASI662MC versus older ZWO planetary cameras
In comparison to certain older models, both ZWO cameras offer several advantages. Firstly, the employment of the latest Starvis 2 technology in the Sony IMX662 and IMX678 sensors brings forth notable improvements, such as zero amp glow and enhanced sensitivity to near-infrared light. Additionally, the introduction of the new HCG mode effectively minimizes read noise at higher gain settings. The ASI662MC can be considered an upgrade over the ASI462MC, which was initially released in 2020, while the ASI678MC serves as an upgrade to the older ASI178MC, first introduced in 2015.
In Sum
Overall, both the ASI662MC and ASI678MC are excellent cameras for capturing the planets and the moon within our solar system. From a technical standpoint, the main distinctions are as follows: the ASI678MC offers a higher resolution, faster FPS, and reduced read noise at an additional cost of $50. On the other hand, the ASI662MC provides a higher Quantum Efficiency (QE) and a larger Full Well Capacity per pixel. Both cameras utilize a 12-bit Analog to Digital Converter that can be scaled down to 10-bit (known as RAW16 vs RAW8) to enhance the frame rate. In comparison to older models, the newer ZWO models incorporate STARVIS 2 technology, resulting in zero amp glow, as well as an HGC (High Conversion Gain) mode to minimize read noise and maintain a wider dynamic range at higher gain settings.
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