On loan from a friend, I could spend some clear nights with this short-focus flat-field refractor. It has 70mm aperture and 350mm focal lenght, for an F/Ratio of F/4,9. It delivers a nice illuminated field and pinpoint stars almost to the corners of the frame. Some slight blue fringing is present near the corners. Focusing is very critical, and also very temperature-dependent. An autofocuser is almost indispensable to keep control over the focus.
![](https://i0.wp.com/www.drogenberg.be/wp-content/uploads/2020/01/Aldebaran_Zonder_filter_2-St.jpg?resize=525%2C351&ssl=1)
![](https://i0.wp.com/www.drogenberg.be/wp-content/uploads/2020/01/Aldebaran_Optolong_Nikon_D750_TecnoSky_AG70_5x120s.jpg?resize=525%2C352&ssl=1)
![](https://i0.wp.com/www.drogenberg.be/wp-content/uploads/2020/01/Cone-Xmas-Nebula-BW-NikoD750-TecnoSky-AG70-Optolong-25x120s-800ISO.jpg?resize=525%2C340&ssl=1)
![](https://i0.wp.com/www.drogenberg.be/wp-content/uploads/2020/01/NGC_2244_ST_St-avg-18605.0s-WC_1_3.0_none-x_1.0_LZ3-NS-full-qua-mult-sc_BWMV_adv-AAD-RE-MBB20_6thLNC_it6-mod-mod-St-v2.jpg?resize=525%2C223&ssl=1)
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