Adapter for Sony E-mount cameras and RASA 8
If you use a Sony mirrorless camera (e.g. A7-III) you probably know how difficult it is to attach it to a RASA 8 telescope. To some it seems simply impossible for three different reasons. First, the RASA 8 telescope has a very short backfocus – the sensor must be 28.73 mm from the front of the telescope. The telescope doesn’t leave much room for connection. Secondly, the camera sensor is large and placed very close to the front edge of the instrument. Third, the camera housing leaves almost no room for the wide cap that the telescope requires.
However, it turns out that clever geometry can solve this difficult connection problem. I’ve created an Astrodevice adapter that not only allows you to connect your mirrorless Sony to the RASA 8, but also allows you to screw in a 2″ filter, giving you a full-fledged set up for astrophotography work. In addition, the adapter is equipped with a special key that allows you to easily attach and remove the accessory from the camera.
To use the adapter you don’t have to calibrate anything – all you have to do is unscrew original glass window from front of the telescope. If you use a filter, it is recommended by the telescope’s manufacturer anyway. For those who would like to photograph in the fullest spectrum of light, it is recommended to put on a regular 2″ UV/IR filter.
Sony E-mount to RASA 8 adapter
The device is also equipped with a unique system that, as far as I know, is used exclusively by Astrodevice. It’s a Front Tilting Mechanism that allows you to adjust the tilt of the sensor from the side of the telescope. If you find that the shape of the stars is non-uniform, you can make the appropriate adjustment, as is the case with dedicated cooled cameras for astrophotography equipped with large size sensors.
The unit is built using 3D printing from carbon fiber reinforced PET-G material. The technological dimensional tolerance is 0.1 mm.
Going full-frame with RASA 8
The RASA 8 telescope was designed to guarantee ideal image quality up to APS-C format. Full-frame sensors are much larger than this. Therefore, when using full-frame cameras, you can expect vignetting of varying geometries, depending among other things on the design of the camera itself. For example in Canon Ra cameras dedicated to astrophotography the vignetting takes on quite a classical shape but from the top and bottom an even, linear, darker framing is visible. Similarly, vignetting will occur in cooperation with other full-frame cameras (e.g. Sony). This is quite normal, but it is good to know what you should expect. These darker areas can be corrected to some extent with flat frames and the remaining imperfections can be removed in post-processing, possibly by cropping the image to a slightly smaller format. This edge processing will also help to deal with the optical imperfections that appear when working with large sensors and small backfocus.