My first Magazine Sky & Telescope - 04.2019

phy, Sony cameras are compatible with many motion-control devices and bulb- ramping intervalometers. However, for deep-sky imaging many imagers like to use a laptop with specialized camera control software to run their DSLRs. Unfortunately, Sony users are out of luck, as none of the popular control programs (AstroPhotography Tool, ImagesPlus, MaxIm DL, Nebulosity, or PRISM) support Sony cameras. To run the Sony at the telescope I used a simple $50 Vello intervalometer that connects to the α7 III through its micro USB port to control the shutter. It’s what I also use to shoot simple time- lapses with the Sony because, unlike all current Canon and Nikon DSLRs, the α7 III lacks a built-in intervalometer. File Compatibility For all testing I set the Sony to shoot in uncompressed RAW mode, produc- ing ﬁles 49 megabytes in size. However, the issue with raw ﬁles from DSLRs and mirrorless cameras is that no two cam- eras’ ﬁles are alike. Software companies update their raw developers several times a year to open and decode ﬁles from new cameras. The mainstream raw developers all opened and decoded the α7 III’s ARW raw ﬁles ﬁne, with one issue. pu The Sony mirrorless cameras excel at low-light videography and in formats up to UltraHD or 4K, which the α7 III can shoot at 24 or 30 frames per second and at either 60 or 100 megabits per second. This is a still frame from a 4K aurora movie captured at 24 fps/100 Mbps and at ISO 25,600 using the Venus Op- tics 15-mm lens at f/2. Among specialized astronomy programs I could test, Nebulosity 4.2 decoded Sony’s raw ﬁles, but DeepSky- Stacker 4.1.1 could not, as it uses the obsolete “dcraw” decoding module. AstroPixelProcessor 1.07 can’t open Sony ARW ﬁles at all. PixInsight 1.8.6 did open and decode the α7 III’s ﬁles ﬁne using the new RAW support module, which replaces the obsolete DSLR_RAW module that shipped with older versions of the program. Make sure the module is replaced when you update the program. q Left: Control options for Sony cameras are limited. An external intervalometer such as this Vello unit connects to the camera through its micro USB port (arrowed) to operate just the shutter for time-lapses and deep-sky images with the camera on Bulb mode. Right: Due to a mirrorless cam- era’s thinner body, attaching it to a telescope with a fi eld fl attener will usually require an additional adapter to supply the correct lens-to-sensor distance. This is a Metabones adapter between the Sony and a Hotech fl attener equipped with a Canon T-ring. Stars or Noise Astrophotographers have criticized Sony’s mirrorless cameras for a ﬁ rm- ware “improvement” the manufacturer introduced in 2017 that eradicated faint stars in raw ﬁ les. This was an unwanted side effect of noise smoothing applied internally to exposures longer than 4 seconds. Such behavior would be unac- ceptable for serious astrophotography. I found the Sony α7 III does not suf- fer from “star eating.” In images taken of the same targets with the Sony and with the Canon 6D MkII and Nikon D750, cameras that have never been accused of eating stars, the Sony showed stars to the same limiting magnitude and just as sharply. The “star eater” effect was simply not an issue. Other artifacts were more serious. sk yandtele scope.com • A PR I L 2 019 63

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