Wednesday, 20 June 2007

Small Astrophoto Tour 2007-06-18/19

Yet I am testing my Baader U Filter. So, I tried to take again a picture of the Venus atmospheric features with my C8 Celestron from Majadahonda. In the previous post referred to Venus imaging, I showed a firsts UV picture. But there is something strange... it seems that a ghost image appears superposed to the main image. After some research in the technical specifications I discovered that the Baader U-filter has some small transmission in the NIR. If the observed object doesn't has a large emission in the UV, the NIR contribution can achieve the same magnitude. It should explain the detection of superposed double images slightly separated by the atmospheric refraction. In consequence, to use adequately the Baader U-filter it is necessary to combine it with a NIR blocking filter or a blue wide band filter to remove the NIR contribution.

The following image is the first result after combining the U-filter with a NIR blocking filter (the Astronomik NIR blocking filter, the Baader one blocks also the UV). In order to increase the exposure, instead the Toucam Webcam Pro, I used a CCD (Meade DSI) with a filter wheel. However, due to a large seeing and the low height of Venus at the imaging, large atmospheric distortions affected the image. After the stack of 10 images with 0.7 secs exposure, this is the best I achieved. Yes... I know any atmospheric feature is visible. Next time I will image early and with a better seeing.

After the Venus set, all the equipment was mounted. So I decided to perform a small astrophoto tour. The next image is the result to combine 40 images of Jupiter of 0.003 secs each.

The image shows the M22 Globular Cluster. For the generation of this image, 80 images of 15 secs were combined.