Mastering Deep Sky Stacker: astrophotography software for processing

Don’t let the plain interface fool you. DSS is a mature, stable piece of software with thousands of great images to its credit. By understanding its workflow and respecting its constraints, you’ll turn scattered subs into a solid foundation for your astrophotography edits.

Deep Sky Stacker is an astrophotography software programme for processing (DSS) and is often a beginner's first real foray into post-processing. It certainly was for me. It's free, reliable, and surprisingly powerful—if you know how to use it. In this expanded guide, we walk through every step of the process using real interface insights, tips, and common mistakes to avoid.

If you haven't already you can download Deep Sky Stacker from here before you start. DSS is native to a PC, but you can run it on a Mac using Wine or similar. Check this link out here.

Step 1: Launch DSS and Get oriented once opened, DSS greets you with a basic interface. The toolbar has options like "Open picture files," "Open dark files," and "Register checked pictures." To the left, there's a log pane that will update with stacking actions. The central pane is for previewing and working with loaded frames. While it’s no Photoshop, its simplicity makes it less intimidating for first-time users. It can be confusing though and today when we expect apps to look beautiful and function equally well. Stick with it though. it has definitely helped me out of a few holes from time-to-time.

Step 2: Import Your FramesClick "Open picture files" to load your light frames (actual photos of the night sky). Use "Dark files" to load dark frames, and likewise for flats and bias. Each frame type plays a role in cleaning your data:

Lights contain your target image.

Darks remove sensor noise.

Flats correct for vignetting and dust.

Bias help clean up read noise.

Keep a structured folder system for each frame type. DSS doesn't auto-detect frame types, so naming and organizing upfront saves frustration later.

Step 3: Register Your FramesOnce all files are loaded, check each list and ensure frames are recognized. Hit "Check all" and then "Register checked pictures." A pop-up allows you to set star detection threshold (start at 10%) and choose a stacking method.

DSS analyzes each frame, aligns them using stars as reference points, and scores them based on clarity. You’ll see scores in the list—sort by score and uncheck low-scoring images that may degrade your final stack.

Pro Tip: Star detection too low? Increase exposure or sharpen your focus next session. DSS relies on clear points of light.

Step 4: Stack the FramesNext, click “Stack checked pictures.” This brings up the “Stacking Parameters” dialog:

Result Tab: For standard imaging, keep “Standard” selected. Use “Mosaic” for wide-field or multiple imaging sessions.

Light Tab: “Kappa-Sigma Clipping” is a great default for removing outliers like satellites.

Dark/Flat/Bias Tabs: Defaults usually suffice unless artifacts appear in the final image.

Output Tab: Check “Create output file in 32-bit” for preserving detail.

Click OK to start stacking. This may take time depending on image count and resolution. Monitor the progress bar and log for any errors.

Common Pitfall: If DSS crashes during stacking, check if you’ve mixed image sizes or orientations. It’s picky about uniformity.

Step 5: Review and SaveOnce stacking completes, you’ll see a washed-out version of your image. This is normal—DSS applies no automatic stretching. Click "Save picture to file" and choose 16-bit or 32-bit TIFF. These formats retain the detail necessary for further processing in tools like Photoshop, PixInsight, or Siril.

You can apply a basic stretch using the sliders below the preview pane, but avoid over-processing at this stage. DSS isn’t built for full editing.

Optional: Batch Mode and Settings TemplatesIf you image often, consider saving your settings as a template. DSS also offers batch processing, though its simplicity can sometimes be a limitation. More advanced workflows may migrate to other tools, but DSS remains a reliable stacker for your astrophotography images.