This magnificent nebula radiates almost entirely in a deep beautiful red. Unfortunately, this color is EXTREMELY hard to detect and record on modern DSLRs. The red is caused by molecular hydrogen re-emitting light at a very specific wavelength, 656.3 nanometers for the curious. In fact, the glowing and tenuous red halo is made up of hydrogen clouds lit by the bright white hot “0-type” stars in the middle. This nebulosity is basically impossible to see with a telescope from the suburbs but the bright stars in the center stand out nicely for framing. The following illustrates just how impossible it is to see this visually.
First of all, this photograph is actually 60 exposures all “stacked” on top of each other. (I mention “stacked” because they stacking algorithm does not strictly sum but adaptively weights averages and avoids saturating pixels). Each exposure itself is 30 seconds long equating to a grand total of half an hour of cumulative exposure time. Nonetheless, once I got inside and spent half an hour processing and stacking the images this is what I saw.
WTF.
Yes, after half an hour of leaving the shutter open in front of an 80mm telescope this is what I had to show for it. I was worried I had spent most of the night tending to my setup only to have a very uninteresting star field to show for it. I had to go to work post processing it and only after much effort was I able to tease out the red nebula. However, it was there all along, sitting at the very bottom of the data only slightly above the background noise. It is helpful to imagine this as an 3 dimensional image. The 3 dimensions correspond to pixel locations sitting on the “ground” and the intensity levels rising up in space. For example, think of a sandbox with a sandcastle sitting in the middle of it. If “height” stood for intensity in a corresponding 2-d image, then the peaks of the castle correspond to the brightest spots. So if my image were represented in this method, it would look like a sandbox speckled with long soda straws (representing the bright stars). Our nebula would look like a pancake partially buried in the sand among a forest of straws.
In order to “pull out the pancake” a bit of photo editing magic must be invoked. In photonerd speak these tools are known as “levels and curves”. Levels basically lets you redefine the upper and lower bounds of your data and expand the remaining data to fill the original allocation. This has the effect of getting deeper blacks and spreading out the brightness levels more evenly but at the expense of “brightness resolution”. Curves however is a bit more sophisticated tool. It is absolutely indispensable and at the heart of any astrophotography post processing. Curves lets you separate out certain pixels of a certain brightness and either amplify or mute them relative to the rest. You can differentially amplify bright or dark parts of the image! This is exactly what was needed. After an hour of running back and forth between these tools, my nebula finally surfaced. (Along with some other techniques I’ll write about sometime later).
This is why astrophotography appeals so deeply to me! I am able to capture and image objects out in deep interstellar space that I cannot ever hope to detect visually with my observing equipment. I am mining the black recesses of space to expose these amazing celestial jewels… all on my computer.