Sep 112015
 

Here are three different versions of M16, The Eagle Nebula in the constellation of Serpens Cauda. Interestingly, the constellation of Serpens is unique in that it is the only one that is split into two distinct pieces, namely Serpens Caput (the head) and Serpens Cauda (the tail). All of these images have been recently taken using the amazing telescope that I co-share with Australian amateur Jason Jennings. This scope is hosted in the iTelescope.net ‘barn’ at the Siding Spring Observatory, Coonabarabran, NSW, Australia. I’ll write another post about the scope soon, but it is an amazing 16″ f/3.5 astrograph.

This first version is a ‘traditional’ LRGB image, meaning it has been made by taking separate images using Clear (Luminance), Red, Green and Blue filters and then combining those to make a final colour image. This should be close to how the eye would perceive the colour because the R,G and B filters pass frequencies of light similar to the sensors in our tri-colour vision system. The clear filter is used as a luminance channel and is where most of the sharpened detail resides.

As with all the images, please click on them to see a full-sized version.

M16 LRGB Version

This next version is taken using three narrowband filters. These are H-Alpha (Ha), OIII and SII. The wavelength of these filters are commonly used by astronomers because there are a lot of emission nebulae that have excited atoms in them that emit light in these wavelengths (especially Ha which is nearly always the strongest). So, to produce an ‘RGB’ image from them requires that they are mapped to the Red, Green and Blue channels of the image. I have chosen to use the ‘Hubble Palette’ which maps the SII to Red, Ha to Green and OIII to Blue. Here is the result:

M16 Narrowband Version

You will notice that the star colours are not good in the narrowband version and this is a consequence of the filter mapping and also because of the relative strengths of the three channels. So, in the third image below, I have combined the stars from the RGB image with the nebulosity from the narrowband image. Here it is:

M16 – NB with RGB stars

I’m not sure which version I prefer!

Finally, a 4th image (I lied!) taken last year with a longer focal length instrument (12″ f/9 RCOS) which shows the ‘Pillars of Creation’ in more resolution. This was also taken using the Hubble Palette which is appropriate because the iconic pillars were made famous by those fabulous images from the Hubble telescope.

The heart of M16

 Posted by at 2:13 pm

An Old Favourite Reprocessed – The Pleiades

 Deep Sky, Image Processing  Comments Off on An Old Favourite Reprocessed – The Pleiades
Dec 072012
 

From time to time it becomes apparent that your image processing skills have improved to the point where you become convinced that it would be possible to reprocess old data and stun the world with the results!

I often find, however, that the improvements are minimal, and that is probably the case here, but I still find this target fascinating. Here is a re-processed image of M45 – The Pleiades, which is currently well placed in Northern Hemisphere skies. Jupiter is not too far away too.

I captured this data in September 2011 using a QHY-8 one-shot colour CCD camera (which I have since sold!). The telescope was my little 75mm Pentax APO refractor. I took 20 exposures each of 10 minutes and combined them to produce this.

 Posted by at 3:35 pm

Adding a Splash of Colour

 Deep Sky, Image Processing  Comments Off on Adding a Splash of Colour
Nov 302012
 

Yesterday, I posted the monochrome H-Alpha image of M42, taken in full moon-light. To get the RGB colour data, I will have to wait for the Moon to go away, or will I?

In the image below, I took the RGB (Red, Green and Blue) data from a colour image of M42 I took last year with a one-shot colour CCD camera. The colour image was taken at a much smaller scale with a much smaller refracting telescope, and I had to scale it up in size to align, rotate and fit the new H-Alpha image which I used as the luminosity channel in this image. The colours look a bit washed out here, which happens if you just simply use Ha as luminance, but I think it does look pretty!

It just shows that the colour data does not have to have the full resolution (detail) of the luminance data. This is why astronomers often shoot the RGB data for their images with their cameras in ‘binned’ mode. If you bin by 2×2, it means that you have 4 pixels adding up to make one. The camera becomes twice as sensitive and you can expose for less time to get the same ‘depth’ of image. The downside is that the image has half the number of pixels across and down, so you pay by losing resolution. But we’ve just discovered that doesn’t matter too much!

 Posted by at 9:50 am