Given that its fall and M31 is in good position for viewing, I thought it would be worth capturing some pics. So during our last new moon, I used Lightbucket’s wide-field scope (LB-0002) to capture 30 second exposures in R/G/B x 5 each. My intent was to stack them and really show off some colour contrasts.
Its harder than it sounds. The whole exercise turned out to be a learning experience with Maxim DL. Not only is M31 way too bright to show off these colour differences with such a small image set and small exposure time, but its also a huge object! Of course I already knew this, but I figured the wide-field CCD would be big enough. Not so.
Here is a stacked image showing the core cloud and some of the spiral shadows. Beautiful, but I wanted to glean more details from my images.
So I played with DL’s histogram stretching and this is what I got. Note the “blue-ness” of the cloud is now represented and there is a lot more spiral detail (but I still could not coax any red stars to stick out more). Interestingly, the signal-to-noise ratio takes a hit (see the graininess) when you try to bring out more detail.
So today’s lesson is that when stacking images to coax out detail, you have to strike a balance between getting a clean image with little detail vs. a grainy image with too much detail.