Why You Need Flat Frames for Your Seestar S50 Photos
Using flat frames with your Seestar S50 brings clear advantages, significantly boosting both the visual quality and scientific accuracy of your astronomical images.
Even with its clever sealed design, the Seestar S50 isn’t entirely immune to subtle flaws. You might still notice slight darkening at the edges or tiny dust particles casting shadows. Flat frames generate a precise map of these problems, which is then used during the image stacking process to eliminate them. The result? A clean, artifact-free background. By effectively removing light falloff and dust, flat frames create a much more uniform image background. This uniformity is super important for revealing faint, delicate details of deep-sky objects without amplifying underlying imperfections. Moreover, flat frames help ensure every tiny light-sensing spot (pixel) on your camera chip reacts to light consistently, leading to a more visually pleasing final image.
The Seestar S50’s new Equatorial (EQ) mode allows for longer individual photos, extending up to 60 seconds. While this promises greater detail, it can also expose certain camera quirks, like “weird looking color gradients” or “banding” (stripe-like patterns). In the Seestar’s default Alt-Az mode, the natural field rotation subtly “dithers” these sensor peculiarities, effectively averaging them out. However, EQ mode removes this rotation, making those fixed sensor artifacts much more obvious. Flat frames are the go-to solution for these background issues, becoming an essential tool for anyone using EQ mode.
How to Take Flat Frames with Your Seestar App: A Simple Guide
Taking good flat frames with your Seestar S50 needs a bit of preparation to make sure they work well.
The most important rule for flat frames is that your telescope setup must be exactly the same as when you took your main space photos. This means keeping the focus setting identical and using the same filters (like the built-in dual-band filter or any external ones). It’s a good idea to capture your flat frames right after your imaging session, before you pack up, or first thing the next morning. Temperature doesn’t matter for flat frames, so you can even do them indoors during the day.
The most critical part involves ensuring your light source shines evenly across the front lens of your Seestar. If the light isn’t uniform, it will mess up your flat frames.
Here are some good light sources for your Seestar S50:
| Source Type | Good Points | Bad Points | Seestar S50 Tips |
| White T-shirt/Paper + Digital Screen | Cheap, easy to find | Can be uneven, affected by wrinkles/room light | Often fails in direct sun; works well indoors under bright, even ceiling lights; |
| Dedicated Flat Panel | Very even light, consistent | Costs more | Best for consistent results, but an investment |
| Twilight Sky | Natural light, no extra gear needed | Needs specific sky conditions, hard to get perfectly even | Requires careful timing and clear, even sky |
To use the flat frame feature, ensure your Seestar S50 and its app (available for Android and iOS) are updated to the latest version (v2.4.0/2.5.0 or newer). Look for “Flat Frame shooting” in the app’s imaging or calibration settings. Once your light source is ready, simply tap “shoot” or “start.” You’ll hear three clicks as the Seestar’s internal filters move. The app will then confirm “flat shoot succeeded” if it worked.
Getting the right exposure is super important for good flat frames. You want the “histogram” (a graph showing light levels) to have its main bump around the 50-60% mark, with all the data between 20% and 80%. This ensures enough light is captured without overdoing it. For best results, aim for an ADU (a measure of brightness) between 15,000 and 30,000. If your flats are underexposed (e.g., at 8000 ADU), they can actually make your photos worse. The Seestar app should show you this histogram to help you get it right.
It’s absolutely critical that you use the exact same gain setting for your flat frames as you did for your main space photos. Gain affects how sensitive your camera is to light, and a mismatch will lead to incorrect corrections. While the Seestar’s camera is quite capable even with very short exposures, it’s generally best practice to aim for flat frame exposures of at least 1 second. The Seestar app will automatically adjust the exposure time to hit the right brightness based on your light source.
Table 2: Recommended Flat Frame Exposure Settings
| Setting | What to Do | Why it Matters |
| Gain | Match your main photos | Crucial for accurate correction; wrong setting causes new problems |
| Exposure Time | Let the app decide (aim for >1s if possible) | Helps avoid issues with super short exposures; app adjusts automatically |
| Histogram Peak | 50-60% (data spread 20-80%) | Ensures sufficient light for good correction without being too bright; app shows you this |
| ADU Target | 15,000-30,000 | Ideal range for astronomy cameras; prevents underexposure that can ruin images |
While the Seestar app handles how many flat frames it takes, astrophotographers generally recommend capturing enough to smooth out any random noise within the flat frames themselves. This creates a super clean “master flat.” Typically, 10-20 frames or 30-50 frames are recommended for astronomy cameras. For the Seestar’s low-noise camera, about 30 frames are often sufficient for a really good master flat. Taking more flats helps make them even more precise.
One of the best things about the Seestar S50’s updated system is its automatic nature. Once you successfully take flat frames in the app, they’re saved and automatically applied to all your future imaging sessions. This works just like how the Seestar handles its dark frames and dead pixel map. The device creates a master dark frame at the start of each session and applies it to your individual photos before it combines them live and saves the FITS files. This means that when you download these FITS files to use in other editing software, you usually don’t need to add separate darks, flats, or “bias frames” yourself. If you try to apply them again, it will actually mess up your image because they’ve already been processed by the Seestar.
Dealing with Issues: Common Flat Frame Problems and Fixes
Even with careful use of flat frames, you might run into problems. Knowing what causes them and how to fix them is important for successful astrophotography.
Sometimes, even after using flat frames, your images might still have uneven lighting or “gradients.” It’s crucial to distinguish between two types: “Optical gradients,” caused by things like vignetting or dust inside your telescope, are fixed by flat frames. They often look like subtle rings or darkening towards the corners. “Sky gradients,” on the other hand, come from outside sources like city light pollution, moonlight, or natural skyglow. These usually appear as a gradual brightening from one side of the image to the other. Even in very dark skies, the Earth’s atmosphere itself can create a subtle gradient. Flat frames do not fix these environmental gradients. For sky gradients, you’ll need special tools in external editing software like GraXpert or Siril’s Background Extraction feature.
As mentioned, when using EQ mode, the camera’s fixed position can make sensor quirks like banding and color blotches more noticeable. While flats are designed to help, they might not always completely fix these issues. ZWO has indicated plans to improve “dithering” (tiny shifts in the camera’s position) in EQ mode with future updates, which should help average out these patterns. Some users have found a clever trick: using the “framing” or mosaic mode with a slight zoom (e.g., 1.1x) or a small angle change (e.g., 1°) even for single targets. This subtly moves the target on the sensor across different photos, acting like dithering and helping to reduce banding. Keep in mind this might slightly increase how long it takes to capture your photos. For stubborn problems, advanced editing software like PixInsight or Siril have powerful tools to clean up these artifacts.
Sometimes, flat frame capture fails, especially if you try to do it outside in bright, direct sunlight. This usually happens because it’s hard to get perfectly even light, or the camera gets overexposed. The best solution is to move indoors and use a bright, even ceiling light. Also, make sure your t-shirt or paper diffuser is stretched smoothly without wrinkles. If you’re using a digital screen, adjust its brightness to hit the recommended histogram/ADU target. The Seestar app’s live feedback is key here to avoid making the flats too bright or too dark.
Table 3: Flat Frame Troubleshooting Guide
| Problem | What’s Likely Causing It | How to Fix It |
| Gradients (rings/dark corners) | Vignetting/Dust (flat frame issue) | Re-take flats carefully, ensure proper setup and exposure (see Table 2); check diffuser is smooth |
| Gradients (side-to-side) | Light Pollution/Syglow/Moon (sky issue) | Flats don’t fix this. Use external background extraction software |
| Banding/Color Shifts in EQ Mode | Camera quirks in EQ mode | Try 1.1x framing workaround; wait for ZWO dithering updates; use external editing tools |
| Flat Capture Failed | Uneven/Too-bright light source | Move indoors; adjust screen brightness; ensure diffuser is smooth |
Top Tips for Using Flat Frames with Your Seestar S50
Following these best practices will help your Seestar S50 flat frames work their magic for your astrophotography.
Even though your Seestar S50 saves flat frames, you need to re-take them if anything changes with your telescope setup. This includes any change in focus, different filter settings, or any physical disturbance that might shift dust. Even without specific changes, redoing your flat frames every couple of months is a good habit to account for tiny shifts or new dust.
To get the most out of your flat frames, always ensure your light source is perfectly even across the front of your telescope, avoiding direct sunlight. Get the exposure just right by watching the app’s histogram or ADU readings, aiming for that 50-60% peak or 15,000-30,000 ADU target. And always, always use the exact same gain setting for your flats as your main photos. While the Seestar handles flats automatically, if you want ultimate control and even better results, you can save the individual FITS files and process them in advanced software like Siril or PixInsight. Just remember that flats fix telescope issues, not light pollution, so you’ll still need other tools for those sky gradients.
Final Thoughts
The new flat frame feature in the Seestar S50 is a big step forward, helping you get cleaner, more even, and more detailed space photos. By understanding what flat frames do—fixing optical flaws like dark corners and dust—and how they help with issues like banding in EQ mode, you can truly boost your imaging results. The Seestar app makes taking flats easy, guiding you to use a uniform light source, correct exposure, and matching gain settings. Since the Seestar automatically applies these corrections, it simplifies your in-app experience. For those who want maximum control, however, exporting the pre-processed files and fine-tuning them in advanced editing software provides a powerful avenue for further refinement. Learning to use flat frames is a rewarding part of astrophotography.
