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One-shot color cameras are what most people think of first for astrophotography. But are they the best choice for you? Credit : ZWO Optics

Astrophotography beginners often ask, “Should I get a monochrome or a one-shot color camera?” There are advantages and disadvantages to each. This article will compare the ZWO ASI1600MM Pro monochrome camera with the ZWO ASI294MC Pro camera.

One-Shot Color

One-shot color cameras, or OSC for short, are what one typically thinks of when thinking of a camera. Just like a DSLR or smartphone, all visible wavelengths are captured at once, through the red, green, or blue filters imprinted on the camera sensor. In a color image, each image pixel consists of four pixels grouped together: one red, two green, and one blue. These pixels are combined to create a single RGB color pixel, then interpolated to regain the full resolution of the image. The micro-filter array on the sensor is called the Bayer matrix.

Bayer Matrix. Credit: Cburnett (Creative Commons)

For the astrophotographer, this means that you only need to take one image to get all colors, which saves time compared to monochrome cameras. For those with few clear nights, this is especially advantageous. In addition, OSC images are easier to process – no need to combine multiple monochrome image filters.

Monochrome

Monochrome cameras, on the other hand, do not have the Bayer matrix; every pixel captures any wavelength of visible (and near-infrared) light. To create a color image, you must use filters that pass the specific wavelengths of light desired. The most commonly used are LRGB filters; luminance, red, green, and blue. Imaging this way allows every pixel to count for a particular color, instead of only one-quarter or one-half of the pixels on the sensor. LRGB filters lead to higher resolution and a higher signal-to-noise ratio (SNR).

Using the luminance filter also allows all visible wavelengths to pass, which, while not necessary to create a color image, can greatly increase the detail and signal-to-noise ratio. In addition, the large LRGB filters used with monochrome cameras transmit more light than the Bayer filters do; 90 percent  to 99.9 percent transmission figures are common.  An article in Digital Photography Review1 says that as much as 1 EV (stop) of light is lost through the Bayer filter. Monochrome cameras can also be used for narrowband imaging with artificial color palettes, as well as ultraviolet and infrared imaging for objects such as planets.

Because one must use multiple filters to create a color image, it takes three to four times longer to create a complete image, depending on if a luminance filter is used. Because of the need to use multiple filters to create a color image, the processing is also more challenging and time-consuming.

Comparison

Let’s compare three images of the Orion Nebula (M42): one in monochrome LRGB on the 1600, one in OSC on the 294, and one in narrowband (Ha+OIII) on the 1600.

Orion Nebula with the ZWO ASI1600MM Pro monochrome camera and LRGB filters. Telescope: Vixen na140ssf (140mm neo-achromat). Total exposure: 2 hours in Bortle 5 skies. Credit: AstronoMolly
Orion Nebula with the ZWO ASI294MC Pro one-shot color camera. Telescope: Takahashi FSQ-106N.  Total exposure: 1 hour in Bortle 3.5 skies. Credit: AstronoMolly

 

Orion Nebula with the ZWO ASI1600MM Pro monochrome camera and Chroma H-alpha & OIII filters narrowband filters. Telescope:Celestron 8” SCT. Total exposure: 2 hours, 41 minutes in Bortle 7 skies. Credit: AstronoMolly

While this is not perhaps the most equal comparison of the two cameras, it gives an example of the differences between imaging with each.  OSC cameras can do narrowband imaging with multi-bandpass narrowband filters, although the SNR is significantly lower than doing narrowband imaging with a monochrome camera.

Conclusion

Both the ZWO ASI1600MM Pro and the ASI294MC Pro can take amazing images. Monochrome cameras have better signal-to-noise ratio and resolution, but require much more time to create a complete image. One-shot cameras capture complete images more quickly and are easier to process, but suffer some transmission and resolution losses due to the Bayer matrix. Many astrophotographers, the author included, end up having one of each.

1Butler, Richard. “Resolution, aliasing, and light loss – why we love Bryce Bayer’s baby anyway.” Digital Photography Review, March 29, 2017. Accessed May 7, 2021. https://www.dpreview.com/articles/3560214217/resolution-aliasing-and-light-loss-why-we-love-bryce-bayers-baby-anyway

MSRP:
ASI1600MM: $1,280.00
ASI294MC: $699.00

Website:  ZWO Optics

About AstronoMolly

I got into astrophotography in July 2015 after receiving my first telescope as a gift, Much trial and error later, I now have three astrophotography rigs set up in my backyard just north of Berkeley, CA, in the San Francisco Bay area, including one dedicated to variable star and exoplanet transit observations. I love doing STEM and astronomy outreach, and I've accrued more than 150 hours of volunteer activities reaching over 20,000 people, both in-person and virtually. I am an AAVSO Ambassador (American Association of Variable Star Observers), an Explore Alliance Ambassador, and a panelist and broadcaster for The Astro Imaging Channel weekly YouTube show. I have a B.S. in Physics from Washington State University, and am currently pursuing my PhD in Physics at University of California, Berkeley, studying neutrinos with my two cats, Orion and Apollo.

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