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Enter the CCD


At the back of every digital camera or webcam is a CCD that captures photons to make the image. Albeit useful for astrophotography (eg the DSLR and webcam images you see on other pages of this site) they have certain disadvantages. They are not made to expose for minutes at a time, and usually have filters in front of them that also degrade their performance. The purist's solution is the ccd camera, which is a computer controlled ccd that goes straight into a scope where the eyepiece should. Most ccd cameras nowadays offer some degree of cooling of the ccd, as any build up of warmth there will cause noise on the image. The result is a very sensitive unit. I am have acquired an ATIK16HR, whch is at the mid-point of current ccd technology. It is a monochrome ccd, of reasonable size, and peltier/fan cooled. It was sourced from Ian King (see links) and I can say I am very happy with it.


January 2007

Enter autoguiding! For those who don't know, these images require pointing a telescope into the sky with extreme precision for extended periods of time. Due to mechanical inaccuracies, it is very difficult just to rely on the electric motor in a mount to move a scope at the same rate as the sky, so a way round this is to mount a second scope shotgun style with the imaging scope, and acquire what is called a guidestar. With a simple crosshair reticule the scope is then kept precisely on the target by a human operator. However modern technology has replaced the human operator with a small webcam in the guidescope, and the corrections are calculated and made by a computer (laptop variety usually). It's not as easy as it sounds to get it all working, the main difficulty is getting the computer to speak to the mount.

Having said that I think I have managed to do it. Help from Alan Buckman at AWR gratefully received, and also from Andy Ellis the Astronomiser who made the PC/mount connection cables and stuff.

Here's the first proper results; all in hydrogen alpha through the ZS66, 5 minute exposures, 40 minutes total each.


November 2006

These are images of the Great Orion Nebula taken through narrowband filters (hydrogen alpha, Oiii and Sii) then put together in various ways. The first image is the most "natural" in that it uses hydrogen alpha for red, Oii for green and blue, and Sii is used as a luminance channel. The other images are false colour mixes of the information, to bring out certain details or just for good looks!







October 2006


M45, the Pleiades or Seven Sisters. 40 mins through the ZS66, with a CLS filter.

This is a monochrome image, artificially turned a bit blue to make it look like it's a real colour image. Tricky eh?



The spiral galaxy M33 seen face on; imaged in Ha only to show structure.


and now in colour.......


M45, the Pleiades or Seven Sisters


And finaly a very quick M42 in Ha from the Great Orion Nebula



M27, the Dumbell nebula



A planetary nebula, which is in fact a load of hot excited gas expelled by a shrinking star. This was called the Dumbell as in a scope, there is what is called a bipolar structure. It's all to do with magnetic fields shaping the gas as it expands, but basically it looks like a dumbell. A bit.




M52 open cluster and the Bubble nebula



Another planetary nebula, and it least this time it looks like a bubble. Astronomy is full of objects that are supposed to resemble something familiar, and look nothing like. I am sure psychologists who specialise in ink blots would have a field day. (see also "the small smudge nebula", the "I can't quite see it nebula", and the "dandruff on your eyepiece nebula".) Done with a Williams Optics ZS66 scope, which is smaller than your average bottle of Merlot, but has a handy field of view so both objects fit in the frame.


M31 the Andromeda galaxy



Our nearest companion galaxy, 2.2 million light years away and closing on us fast. Just simple monochrome for this one, but 70 minutes of total exposure to grab it. Note the dust lanes and the fact that you can identify the brighter stars. Not also two companion galaxies, the first at about 10 0'clock from the main galxy centre, the second just on the bottom edge of the frame at about 5 o'clock and mostly off frame. This is a massive object 6 moon widths in size, and will require at least 4 more exposures to make up a mosaic of the full galaxy.


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