Start with the image you have

If you’ve taken a single DSLR or mirrorless photograph, the simple editing steps in my first astrophoto guide are a good starting point. A smart telescope’s app already produces a processed image, which you can enjoy as it is or use as a starting point for further editing.

For my deep-sky telescope images, I use PixInsight. It has a steep learning curve, but it gives me the tools to turn a collection of exposures into a finished photograph. My PixInsight review explains why I like it and what to expect.

Turn your exposures into a stack

A telescope project usually starts with a set of light frames, also called subframes or subs. Pre-processing means calibrating those exposures, aligning the stars, and combining the usable frames into a stack. This gives you a better starting point for bringing out the faint detail.

My PixInsight pre-processing guide walks through the terminology, organising your files, and working with data from one or more filters and sessions. Start there if you have a folder of exposures and aren’t sure what to do next.

What processing brings out

Here’s M13, the Hercules Globular Cluster, from my Bristol garden. The stack contains eight hours of exposures. Processing helps turn that starting point into a photograph, balancing the background, colour, and detail. There’s a surprising amount hiding among those stars!

Have a go with my data

Fancy trying your hand at the Iris Nebula? Download my stack and see what you can bring out. There’s plenty of faint dust to tease out, even from a city!

The Iris Nebula

30 hours from Bortle 8 skies in Bristol.
360 × 5-minute exposures, captured in July and August 2024.

Askar 130PHQ, ZWO ASI2600MC Pro, and Optolong L-Quad Enhance filter.

Both files contain the same image data, so you only need one. Choose XISF for PixInsight, or FITS for other astrophotography processing software that supports FITS.

Download XISFPixInsight · 302.1 MB Download FITSOther astro software · 288.2 MB

Files open in Google Drive in a new tab. If it says “No preview available”, choose Download to save the stack.

The downloadable files contain the untouched output from PixInsight’s Weighted Batch Preprocessing (WBPP), with no further processing applied. The stack is still linear (unstretched), so it may look almost black when you open it. That’s normal! Use your software’s automatic screen stretch to see the faint detail.

Read the accompanying notesWatch my Iris Nebula walkthrough

You’re welcome to share your processed image. Please credit the image data to Lee Pullen / Urban Astrophotography, and the processing to yourself.

The tools and my approach have changed over time, so older videos may look a little different from a current installation of PixInsight. Follow one example through, keep your original data, and come back to it as your skills improve.