Category: Deep Sky

The 20″ was working well on Tuesday evening with both tracking and guiding doing a good job of keeping the stars round. Out of 41 images of NGC 891 I only threw 2 away where the stars were less round.

Due to the high altitude of the target exposures were kept short at 30 seconds and binned 2×2. Guide exposures on the STV were 1.5 seconds with the aggressiveness turned down to 70%.

Overall dimentions are 13.1′ x 2.8′ and the dust lane is showing some detail in this picture.

Whilst at the Kelling star party I had a talk with Bernard from Modern Astronomy about cameras and specifically the Kodak KAF-8300 chipped models. I’d been thinking about a single shot colour for the astrotrac setup and the QHY9 looked a good match for a very good price. I placed an order and delivery was via Fedex within 2 days.

I’d had the idea in my head that the cooled colour CCD camera would be a low noise, high sensitivity version of the DSLRs I’ve been using but some test shots revealed that this isn’t entirely true. Initial pictures were a little disappointing and it wasn’t until I was reading an article on setting the offset and gain levels for the camera (http://www.stark-labs.com/blog/files/GainAndOffset.php#unique-entry-id-6) that the pieces fitted together and illumination dawned.

You can get surprisingly good pictures with short exposures on DSLRs by increasing the ISO rating. This is effectively increasing the gain and it’s not a free lunch. Noise is amplified as well and dynamic range is reduced. With the CCD, once you’ve calculated the optimal gain you set it and never alter it again. This level will be a lot lower than the DSLRs value and correspondingly longer exposures are required to fully exploit the increased dynamic range available.

With my Zenithstar 70mm, Astrotrac mounted on a Manfrotto tripod I’m currently limited to 5 minute exposures without trailing so I picked a bright target for a test. M31 is ideally placed for this at the moment and here’s the result resized to about half the original.

12x 5 minute exposures

Zenithstar 70mm

William Optic FFIII field flattener

Friday night was the first opportunity I’ve had to take some pictures of this. Thursday night was also clear but I was busy imaging comet Garradd again, this time passing close to the Coathanger cluster.

Using the club’s ATIK on the 20″ we took 41 30 second exposures binned 3×3 and also 3 each of red, green and blue binned 6×6. This really wasn’t enough colour frames and after a lot of effort I gave up trying to get a colour image and just stacked the luminance frames.

Sn2011fe is a type 1a supernova a mere 21 million light years away.

Living within a spiral galaxy gives us the chance to get an up close view of the dust clouds that fill the inter-stellar space in the spiral arms. If it wasn’t for this dust obscuring the starlight from millions of stars then our night sky would look very different.

This image is a wide-field view of the area around Cygnus. Six exposures of 3 minutes each at ISO 800 and f/3.5 with my Sigma 10-20mm zoom.

One of the main attractions of La Palma was it’s views of the Milky Way. It’s southerly latitude opens up views of our galaxy’s centre that just aren’t possible from the UK. This picture is a mosaic of two images taken with the Sigma 10-20mm set at 10mm on my Canon 350D. Each image is a stack of three 3 minute exposures at ISO 800 and f/3.5.

Cygnus and Lyra are at the top of the picture, with Scorpius and Sagittarius at the bottom.