![]() In deep-sky work, a small-aperture, short-focal-length optic is sampled properly with smaller pixels. In fact, there is a place or two in astrophotography to which smaller pixels are very well suited and even preferred. Fast focal ratios and short focal lengths like on this f/2 eight-inch RASA are a great match for small pixels For longer focal-length telescopes, you really need larger pixels to achieve proper sampling and a good signal-to-noise-ratio per pixel. Unfortunately for us, the sensor market cares more about hummingbird photography than it does for imaging galaxies far, far away. Unfortunately for us, there is a big difference between a 5-minute exposure at night through miles of atmosphere and a 1⁄ 2000-second image of a sunlit hummingbird that is four feet away. The drive to “more megapixels” is driven by a desire for more resolution. Twice the pixel size is actually four times the surface area for collecting light. Nine microns in fact, whereas most DSLRs or point-and-shoot cameras at the time had pixels at least half that size. When Sony came out with its A7s mirrorless camera that had such tremendous capability for capturing the Milky Way, people would speculate about what it’s sensitivity secret was. I’ve talked about this relationship before. Professional observatories are usually located where the seeing conditions are as good as can be achieved on Earth.Īll other things being equal, cameras with larger pixels are generally more sensitive to light and have better signal-to-noise characteristics. Big telescopes with long-focal-lengths need really large pixels in order to work effectively, and the same goes for you. But without the use of some sort of adaptive optics, they have the same limitations as you do when you're shooting from your backyard. Sure, professional telescopes are located where the seeing conditions are better than you probably experience. All those gigantic telescopes you see at a professional observatory have to follow the same physical rules we do (and my astronomer friend was surely taking this into account with that 9-micron pixel camera). If you recall when I wrote about pixel scale and sampling before, it is important to have proper sampling to obtain good data to work with. The bread-and-butter CCD sensors, such as the KAF-8300 or the Sony 694, are floating 4- to 6-micron pixels, and some popular CMOS choices are starting to dive below 3-micron pixels. I laughed out loud because in the amateur market, 9-micron pixels are huge by most standards. “I just love those tiny little 9- micron pixels,” he said. While doing some volunteer work at a professional observatory some time ago, I overheard one of the astronomers talking about his new camera. Why does this matter? The drive for smaller pixels is usually about gaining resolution, but in astrophotography, this can also work against us. As a result, it’s getting harder and harder to find cameras with larger pixels. However, CMOS-based sensors for astrophotography are becoming increasingly popular (see my recent article in Sky & Telescope’s May issue on the CCD to CMOS transition). Smaller pixels have both some inherent advantages and disadvantages over larger pixels, but the truth is that in most things that matter, larger pixels are generally better. Pixel size is a big consideration when selecting a camera for astrophotography.
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