While I was out photographing Mars, I also had another target planned: My old favourite, the Andromeda Galaxy. I have photographed the Andromeda Galaxy on several other occasions, but this time I was determined to get a better shot. I decided to spend some extra time polar-aligning my telescope and piggybacking my camera onto it, for more precise tracking. The last time I piggybacked a camera onto a telescope was with a film camera, believe it or not. This time I took full advantage of living in the future with a digital camera and a powerful computer with advanced software for stacking images.

I decided to use my 100mm prime macro lens, for a couple of reasons: First, I wanted to get a slightly wide angle shot of Andromeda, because I like having some context for where things are in the sky. Second, my 100mm lens is of much higher quality than my 70-300 zoom lens, and was more likely to give me better focus and more stable results. I also think it is interesting that I used a macro lens that I purchased specifically to take pictures of extremely small things very close up to take a photo of an object 220,000 light years wide and over 2.5 million light years away.

The photo on the left is the full image of what my camera saw through the 100mm lens. The bright red star towards the bottom of the image, left of centre, is Mirach, which is one of the guide stars that I use to find the Andromeda Galaxy when I'm looking for it. It is a red giant, about 197 light years away. The other guide star I use is μ Andromedae, which is the bluish star halfway between Mirach and the Andromeda Galaxy. It is a relatively young main sequence star, about 130 light years away.

The photo on the right is a pixel-for-pixel (unscaled) crop of the Andromeda Galaxy from the photo on the left. You can see two of Andromeda's satellite galaxies as well: M110 to the upper right, and M32 directly below the galactic centre. Besides those galaxies, every other point of light in these photos is a star in our own Milky Way galaxy.

Technical Details: This photo was taken with my 5D Mark II + EF 100mm macro (piggybacked onto my Meade LX90 for tracking) at ISO 1600, f/4 for a combined exposure time of 36 minutes (12 exposures of 3 minutes each, stacked).