This short report is about my experiences with a f/2 Telescope, the Celestron RASA 8.

This fast Scope allows me to take my pictures in a very short time with acceptable results and details. To achieve this speed the typical secondary mirror of the SC-Telescope is exchanged with a lens and the camera sits in front of the telescope.

This has the advantage of fast speed, but also a lot of troubles to deal with. You have to worry about cable management to minimize weird diffractions. Also using filters can be tricky if you use a camera with a longer back focus distance like the ZWO ASI 2600 cause of the short back focus distance of the RASA 8. But once you taste the possibilities of an fast scope like this, you try to deal with the obvious disadvantages of this system.

For me the speed is such an important advantage, cause for everything else than H-Alpha narrowband imaging, I have to drive out of the city to a dark side of the Black Forest. That's the reason, why I like to get everything out of such a astronomy-tour to enjoy the beauty of deep-space targets.

To deal with the diffraction, I 3D-printed a dew shield with integrated arms for the cables. These 4 arms generates diffraction spikes which are nearly similar like these from classic Newtonians. The printed dew shield is very solid, so I can easily leave it in place for several nights of imaging.

The picture shows my system with the ZWO ASI 1600 MC Pro, but it also works with my bigger camera, the ZWO ASI 2600 MC Pro.

Using the fast aperture f/2 gives me the opportunity to complete a target in just one night out in the Black Forest. It seems that this systems collects 6x more light in the same time than my older f/4 Newton Telescope. Of course there are other troubles with f/2 than the diffraction of the RASA-System. F/2 means, that there is no room for errors in the imaging routine. Focus, collimation and tilt in the adaption of the camera or the filter are the things you have to deal with. In my opinion the RASA-System is not very suitable if you are a fan of perfect star-shape or if you are zooming in extremely. In addition to that the RASA is not the sharpest system on the market.

But it is great for collecting a lot of light in a short time. And the advantage to a fast Newtonian is, that the collimation is very resistant even if you are traveling with the telescope like I do. The collimation itself is a challenge, but once it is collimated, it should last on a long time. A fast Newtonian like a Hypergraph with f/2.8 is very sensitive for loosing the collimation.

Furthermore you have a closed system. With the 12V Fan cooling out is no big problem and you don't have to worry about dust, reflections and Field-Flattener cause of the Correctorplate in front of it. Problems with dew are recently no deal anymore cause of the new Celestron dew-heater ring.

All in all there is for me no better compromise between image quality and fast aperture on the market within the price range of the RASA.

As an example for the fast speed I will show you my picture of the tadpole Nebula (IC 410). For this I have collected only 2 hours of integration time with a duo narrowband filter (the IDAS NBZ Nebula Booster).