First findings

Thanks to the beautiful weather, I have been able to take a lot of photos over the past few weeks and also try out and read a lot.

The pictures were reasonably ok, but I found that the stars are not really beautiful and always a bit misshapen.

Since I had this phenomenon with 30s as well as with 60s or 120s exposure time, I do not think that it is a problem with the tracking. Otherwise this should have been much more pronounced at 120s exposure time than at 30s. But it wasn't.

I also had various problems with editing with PixInsight. The software is extremely extensive and by far the best software for editing astro photos. But correspondingly complex, so I signed up for a course in June and hope to learn a lot there.

Here is a list of what I found out during my research on the Internet:


  • The Atik Horizon CMOS sensor is apparently not able to generate stable bias images, i.e. my procedure for preprocessing (bias, dark, partly flat, light) was wrong and therefore could not lead to optimal results.
    With this (and many other CMOS sensors) you have to work with flat darks instead of bias. However, these must have the same exposure time as the flats. As I have flats with Voyager in the twilight so far, each picture has a different exposure time and is therefore not usable for this procedure. I therefore have to generate the flats with the flatfield generator.
  • Celestron 0.63f reducer. The reducer enlarges the field of view and also flattens it a little, and it also shortens the necessary exposure time by a factor of 2.5. What is unfortunately not in the description is that the back focus also shifts. Instead of 13.9cm, the back focus is now 10.5cm. I didn't pay attention to the back focus, I just positioned the Steel Drive approximately in the middle in order to have as much leeway in both directions. Therefore the chip was 12.1cm behind the telescope, i.e. 1.6cm too far back. As a result, stars are depicted with a so-called coma (looks a bit like a comet). So exactly the effect I see on the pictures.
  • As I read, long exposure times don't help much with CMOS cameras, i.e. the optimal SNR is reached at approx. 30s. After that, the signal continues to rise, but so does the noise. However, I am not sure whether this only applies to uncooled cameras (DSLR) and can be exposed to cooled cameras for longer. The Atik Horizon is limited to 2 minutes. If you want to expose for longer, you have to configure this explicitly, because according to the manufacturer this is not useful. However, I had the feeling with the M82 that the picture with 2min single exposures was better than that with 30s, although the total duration of the exposure was identical. This can also be due to the wrong preprocessing. I'll have to find out.

Next steps:


  • Tests with the same equipment but the chip of the Atik Horizon as close as possible to the correct back focus (10.6 cm should be possible). This should bring a significant improvement in the mapping of the stars.
  • Tests without reducer with correct back focus
  • Tests without reducer with correct back focus and guiding.
  • Tests with different gain settings and exposure times.
Location: 3294 Büren an der Aare, Schweiz

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