How to Focus DMK 31 Series at Long Focal Lengths

Blogged by Jonathan Maron on March 8, 2008 and tagged with FAQ, Sample Images, Jupiter, Moon, Saturn, Mars.

Joe Zawodny wrote to us recently talking about some of the difficulties that members of the astronomy cameras community had been experiencing focusing the DBK 31 series at long focal lengths. He writes:

Saturn is [...] a lot dimmer than either Jupiter of Mars. But then, so are the Saturnian moons. I managed to capture Saturn and 4 of its moons in [the following] image, using a Celestron 11 at f/20 and my DBK 31AF03.AS.

Later in his e-mail, he continues.

Two things I learned in the process. You need to increase the brightness control to bring the noise in the darkest parts of the image above zero counts (use the histogram function). Otherwise, stacking will not allow you to access the information lurking in those regions. In this case it was Enceladus that I was after. The second thing I learned is that the DBK's noise level is still quite low even at very high gain setting. This image was shot with a gain of 880 and an exposure of 1/11 second (with a UV/IR blocking filter). It is a stack of 1600 of the best frames out of 2800. I used the ROI function in IC Capture to allow me to capture so many RGB24 encoded frames and keep the AVI under 1GB for compatibility with RegiStax. I nice challenge with an equally nice reward.

Below is the photo that he submitted:

Thank you Joe for sharing your wisdom with the rest of the astronomy cameras community!