Since some time I had the wish to take photos of larger areas of the night sky. So I bought a refractor with a 90mm diameter objective and 500mm focal length. The objective is a doublet ED lens that reduces greatly the colour aberration compared to achromatic objectives. The manufacturer calls this telescope an apochromatic lens but admits that the colour correction is not perfect. This is alright because a two lens ED objective of 90mm diameter and 500mm focal length cannot completely correct the colour aberration.
I did look through the telescope and observed Vega at high magnification. I could not detect a coloured edge. However, I am primarily an astrophotographer and not a skilled visual observer. Before I bought this telescope I searched the internet for images taken with this refractor, and the I found images were OK for me.
I took the first images with this refractor using a H-alpha filter to deal with the light of the full moon. It worked and the results are satisfying. I am also using the 2" flattener from TS. It might not really be necessary for the size of the CCD-chip in my camera but it certainly won't hurt. Anyway, the stars are tack sharp until the edges.
The refractor is mounted on a universal 3" dove tail plate and can easily be replaced by another telescope. Only the DSBS adapter plate to ount two telescopes in parallel has to be pushed to the center. The refractor and the C5 have the same weight which reduces the need for careful balancing. I marked the DSBS plate with a red tape at the position for using the C9 instead of the 90mm refractor. That makes the exchange of these telecopes very easy and quick. The refractor is operated in the same style as the C9 which is described here. The images with the refractor are taken with an Atik CCD camera while a Watec 120N CCTV camera at the parallel mounted C5 is connected to TVGuider and guides the setup.
