My first Magazine Sky & Telescope - 02.2019

adapter to thread this to the Evostar body ($49) as well as an adapter to connect my CCD camera to the ﬂ at- tener. Note that with the reducer/ﬂ at- tener, the scope is operating at a focal length of 357-mm, producing a focal ratio of just under f/5. My ﬁ rst test was to shoot the Moon with and without the reducer (see below) with a Canon 5D Mark III DSLR. In the center of the ﬁ eld, the Moon was sharp and well-deﬁ ned in both cases, with no color fringing evident photographically. Even with- out the ﬁ eld-ﬂ attener, the Evostar 72 can likely be used for objects near the center of the ﬁ eld of view. Sky-Watcher states all Evostar refrac- tors will satisfactorily cover an APS-C- sized sensor or smaller without the use of a ﬁ eld-ﬂ attener. I put a full-frame DSLR on it just to see how large the usable ﬁ eld is, and I took a test shot of M31 from my backyard. The image shown on the opposite page is a single calibrated and stretched frame which shows just how wide the ﬁ eld of view is. I’ve superimposed a rectangle showing the size of an APS-C sensor’s coverage; it's still plenty to capture all of M31. Naturally, the stars at the edges of the full-frame image are a good bit elongated, but curiously, one of the corners actually held up okay. It is possible there was some tilt in my prototype adapter, or perhaps some sag with a heavy camera attached. Perfor- mance is better inside the crop-sensor rectangle, of course, but still you can see the correction fall off at the edges and corners of the APS-C frame. Any- thing smaller than an APS-C should produce round stars across the entire image, while APS-C detectors will show acceptable stars until you get to the very corners of the frame. Color-wise, there was some lat- eral color separation of stars radially towards the center of the image, with stars displaying a blue edge on one side and a red one on the other. This is normal for a doublet APO in this price range without using a ﬁ eld-ﬂ attener, and I’ve even seen worse on more- expensive APO triplets. A backyard on the far side of Orlando from Disney World is not the best place to do color images, and so I thought I’d try some narrowband with this little scope. A doublet APO should excel when shooting with ﬁ lters as a much narrower range of wavelengths needs to be focused in the same place. Slightly under-sampled on a Starlight Xpress Trius-SX694 monochrome cam- era at f/5, I knew I could get some nice images with short 5-minute exposures, even at narrowband wavelengths. I focused all of these images by hand using the stock focuser. Florida summers are pretty stable temperature- wise, and I focused once and left it for the night. I shot four targets total over several nights in automated runs that included meridian ﬂ ips, and the focuser never slipped. Conclusion I started my astronomical life strictly a visual observer, and now after several t The Evostar 72 Apo performs well on the Moon both with (near left) and without (far left) Sky-Watcher’s reducer/corrector for its ProED 80 refractor. With the reducer/fl attener, the telescope operates at 357 mm, f/4.9. p Although the Evostar 72 can cover detectors smaller than APS-C format with minimal aber- rations as seen on the facing page, a fi eld-fl at- tener is recommended for optimal performance for full-fi eld correction on detectors as large as 24×36 mm. Additional adapters are necessary to properly space your camera’s detector from the corrector for best performance. years as a hardcore imager, I’ve only recently returned to visual astronomy. I must admit, I had forgotten the simple joy of just taking ﬁ ve minutes to set up a telescope for a quick look at an object or two. It really was a pleasure, cer- tainly better than my ﬁ rst experience with a Go To mount and scope combi- nation many years back, which was of course the biggest scope I could afford (the #1 mistake beginners often make). The AZ-GTi is simple, stress-free, and easy to use. The Evostar 72 is a budget APO, and yes, I could tell the difference between it and some of my top-shelf scopes, most of which, however, would require adding an extra zero to the price. It has good color performance in the middle of the ﬁ eld, with only a touch of color visible at the edges when viewing the brightest objects. For astrophotography, I found the Evostar 72 to be a pretty reasonable starter scope, and combined with the AZ-GTi, it’s also a nice, por- table visual package. ■ RICHARD S. WRIGHT, JR. can often be found sharing views of the night sky at his local Starbucks. sk yandtele scope.com • FE B RUA RY 2 019 63

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