The Orion nebula, also known as Messier 42 (M-42), is one of the most splendid winter deep sky targets for amateur astronomers. It can be seen as a faint fuzzy patch for those of us with excellent vision, just below the three belt stars of the constellation Orion.
In binoculars this patch of light shows some sweeping details and groups of stars surrounding the area. Through a modest telescope, the details do start to pop out, and if using a telescope of 16 or more inches in diameter, you will start to get hints of greenish color when viewing through an eyepiece. Unfortunately, the human eye is not the most sensitive to the red light that excited Hydrogen gas gives off (656.3nm), and the Orion Nebula outs out a lot of its light at this wavelength. As a bright nebula, it has become a favorite target for budding astrophotographers: even a small telescope and short exposures of a minute or so will show some very satisfying detail. Here is a color image of M-42 taken with the school’s Takahashi FC-125, a 125mm (5″) diameter refractor. The camera was a Nikon D-810a DSLR, their version of the D-810 but without their IR blocking filter. This allows a much higher sensitivity to the Hydrogen emission lines at 656.3nm. The “a” means astronomy in Nikon lingo. This image is constructed with three separate 60 second exposures, cleaned up by removing bias, dark and flat fields, then merged together to show the bright inner details along with the fainter outer regions of the nebulosity.
The nebula itself is some 1344 light-years from our Solar System and is about 24 light-years across. It is a well studied star forming region, with some of its young stars forming protoplanetary disks, the precursors to solar systems.
I spent some time this morning with PixInsight on a stack of M-42 images. This is the result. PixInsight is an impressive, though oddly challenging, piece of software. The interface still eludes me at times. The results are splendid, however.
This image was taken through a Nikon D-810a at f/4, 200mm, tracked on an iOptron mount in gusty winds. This piece is the result of three major processes:
All images were aligned using stellar centroids.
The images were then stacked… this is an image integration of 100 seconds worth of exposures.
PixInsight was then used to do a Dynamic Background Extraction to essentially perform a flat field thus removing the lens’ vignetting. I still can’t get over this process: no flat fields required… though I bet real flats would result in a better overall image.
The camera does its own internal bias and dark subtraction. The image was then brought into PhotoShop for adjustment to levels and cropping.
Now… compare that colorful image with the monochrome one: that was taken way back in 1986 on Tri-X Pan film pushed to about 1000 ASA by boiling it in nitrogen. The image is a 20 minute exposure through a Celestron C-8 at f/10, manually guided with an illuminated reticle eyepiece. I developed this in my bathroom using duct tape and towels to block all external light from entering.
What a difference! New technology brings better sensitivity and a whole new world of imaging…. but we knew this. I’ve been playing with CCDs since the early 1990s. No surprises. The real surprise? Cost! All this tech adds up in cost. I am not really sure that it saved me a whole lot of time to make the new image with the new tech… perhaps if both images were color? Then, yes, the new tech has saved me time. Simple? M’eh. It’s about the same level of technical detail. It ends up being about one’s knowledge base: software or film developing? You choose. Certainly some of my best images were taken with film. Which do you prefer? It’s totally up to you. Like vinyl records, film is making a comeback, but hasn’t made its way to the realm of astrophotography again. I am pretty sure that CCDs and CMOS sensors are here to stay for astro-art imaging.
PixInsight sounds interesting: check out their site here.