The Rosette Nebula (Caldwell 49) – 23/01/2014


The Rosette Nebula – Click to Enlarge

Plate SOlved Image - Click to Enlarge

Plate Solved Image – Click to Enlarge

This is my first image of another of the finest objects in the sky.  This is the object known as Caldwell 49, or more descriptively, the Rosette nebula.  It is an emission nebula in the constellation of Monoceros.  The image consists of a total of 30x 4minute exposures at ISO800 on my astro-modified Canon EOS 1100D, for a total of 2hrs of data.  It was taken with my Revelation 80mm Semi-Apo refractor, guided using the finder guider and PHD guiding.

The sub-frames were stacked, along with dark, flat and bias frames, in Deep Sky Stacker, then exported as a 16-bit TIFF for finishing in Photoshop and Lightroom.

The heart of this nebula is a stellar nursery, consisting of a cluster of bright young stars known as NGC 2244.  This is quite a difficult object to bring out all the detail in on your first attempt.  It’s surrounded by a large quantity of dim nebulosity, that’s easy to lose in the processing if you’re not careful.

As an example of the process, the following images show the different stages I went through (see gallery below)…

1) A single Sub-frame showing the very faint image left after 4 minutes of exposure.

2) All of the 30 frames stacked – not much different looking to the naked eye, but there’s a lot of dim data in there to come out – honest!

3) My first attempt at processing.  Not bad, but seemed to be missing a lot of the faint nebulosity I was expecting around the edges.  Turns out I’d clipped the blacks in the image, which effectively makes any of the fainter stuff black too. This is easy to do, and is often the mistake that can spoil a great image.

4) My final reprocess.  More carefully stretched, showing way more detail in the surrounding area and the core, as well as being a more natural colour and contrast.

You can flick between the images by using the arrow keys to compare once you’ve brought one up…

The final image was created when I’d had time to go away and let my mind settle.  Processing is a really intensive thing, and very often you can’t see the wood for the trees so to speak.  Also, it can be tempting to be precious about your processing so far, and try to rescue an image when sometime you’re better off (as in this case) going back to the original stacked image and starting again.  Once you’ve clipped the blacks, you’ve basically lost part of the fainter bits of the image, and without undoing that clipping, you’ll never get that back.

I came at this with fresh eyes and more time, and brought out the best I could in it. Very happy with the end result.

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2 Responses

  1. David Trelfer says:

    As you know I’ve on the same road with this one. A question, Is the stacked image as left DSS or what came into PS as I find they are quite different. When I open mine in PS it is totally black with a few stars and no hint of what is to come.
    I still find it amazing from a sub the final image

    • Adam says:

      It’s actually the Autosave.tif opened in preview on the Mac in this case. I find that sometimes it shows nothing and other times you see a faint image as here…

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